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Annotation of gcc/flow.c, revision 1.1

1.1     ! root        1: /* Data flow analysis for GNU compiler.
        !             2:    Copyright (C) 1987 Free Software Foundation, Inc.
        !             3: 
        !             4: This file is part of GNU CC.
        !             5: 
        !             6: GNU CC is distributed in the hope that it will be useful,
        !             7: but WITHOUT ANY WARRANTY.  No author or distributor
        !             8: accepts responsibility to anyone for the consequences of using it
        !             9: or for whether it serves any particular purpose or works at all,
        !            10: unless he says so in writing.  Refer to the GNU CC General Public
        !            11: License for full details.
        !            12: 
        !            13: Everyone is granted permission to copy, modify and redistribute
        !            14: GNU CC, but only under the conditions described in the
        !            15: GNU CC General Public License.   A copy of this license is
        !            16: supposed to have been given to you along with GNU CC so you
        !            17: can know your rights and responsibilities.  It should be in a
        !            18: file named COPYING.  Among other things, the copyright notice
        !            19: and this notice must be preserved on all copies.  */
        !            20: 
        !            21: 
        !            22: /* This file contains the data flow analysis pass of the compiler.
        !            23:    It computes data flow information
        !            24:    which tells combine_instructions which insns to consider combining
        !            25:    and controls register allocation.
        !            26: 
        !            27:    Additional data flow information that is too bulky to record
        !            28:    is generated during the analysis, and is used at that time to
        !            29:    create autoincrement and autodecrement addressing.
        !            30: 
        !            31:    The first step is dividing the function into basic blocks.
        !            32:    find_basic_blocks does this.  Then life_analysis determines
        !            33:    where each register is live and where it is dead.
        !            34: 
        !            35:    ** find_basic_blocks **
        !            36: 
        !            37:    find_basic_blocks divides the current function's rtl
        !            38:    into basic blocks.  It records the beginnings and ends of the
        !            39:    basic blocks in the vectors basic_block_head and basic_block_end,
        !            40:    and the number of blocks in n_basic_blocks.
        !            41: 
        !            42:    find_basic_blocks also finds any unreachable loops
        !            43:    and deletes them.
        !            44: 
        !            45:    ** life_analysis **
        !            46: 
        !            47:    life_analysis is called immediately after find_basic_blocks.
        !            48:    It uses the basic block information to determine where each
        !            49:    hard or pseudo register is live.
        !            50: 
        !            51:    ** live-register info **
        !            52: 
        !            53:    The information about where each register is live is in two parts:
        !            54:    the REG_NOTES of insns, and the vector basic_block_live_at_start.
        !            55: 
        !            56:    basic_block_live_at_start has an element for each basic block,
        !            57:    and the element is a bit-vector with a bit for each hard or pseudo
        !            58:    register.  The bit is 1 if the register is live at the beginning
        !            59:    of the basic block.
        !            60: 
        !            61:    To each insn's REG_NOTES is added an element for each register
        !            62:    that is live before the insn or set by the insn, but is dead
        !            63:    after the insn.
        !            64: 
        !            65:    To determine which registers are live after any insn, one can
        !            66:    start from the beginning of the basic block and scan insns, noting
        !            67:    which registers are set by each insn and which die there.
        !            68: 
        !            69:    ** Other actions of life_analysis **
        !            70: 
        !            71:    life_analysis sets up the LOG_LINKS fields of insns because the
        !            72:    information needed to do so is readily available.
        !            73: 
        !            74:    life_analysis deletes insns whose only effect is to store a value
        !            75:    that is never used.
        !            76: 
        !            77:    life_analysis notices cases where a reference to a register as
        !            78:    a memory address can be combined with a preceding or following
        !            79:    incrementation or decrementation of the register.  The separate
        !            80:    instruction to increment or decrement is deleted and the address
        !            81:    is changed to a POST_INC or similar rtx.
        !            82: 
        !            83:    Each time an incrementing or decrementing address is created,
        !            84:    a REG_INC element is added to the insn's REG_NOTES list.
        !            85: 
        !            86:    life_analysis fills in certain vectors containing information about
        !            87:    register usage: reg_n_refs, reg_n_deaths, reg_n_sets,
        !            88:    reg_live_length, reg_crosses_call and reg_basic_block.  */
        !            89: 
        !            90: #include <stdio.h>
        !            91: #include "config.h"
        !            92: #include "rtl.h"
        !            93: #include "basic-block.h"
        !            94: #include "regs.h"
        !            95: 
        !            96: /* Get the basic block number of an insn.
        !            97:    This info should not be expected to remain available
        !            98:    after the end of life_analysis.  */
        !            99: 
        !           100: #define BLOCK_NUM(INSN)  uid_block_number[INSN_UID (INSN)]
        !           101: 
        !           102: /* This is where the BLOCK_NUM values are really stored.
        !           103:    This is set up by find_basic_blocks and used there and in life_analysis,
        !           104:    and then freed.  */
        !           105: 
        !           106: static short *uid_block_number;
        !           107: 
        !           108: /* Number of basic blocks in the current function.  */
        !           109: 
        !           110: int n_basic_blocks;
        !           111: 
        !           112: /* Maximum register number used in this function, plus one.  */
        !           113: 
        !           114: int max_regno;
        !           115: 
        !           116: /* Indexed by n, gives number of basic block that  (REG n) is used in.
        !           117:    Or gives -2 if (REG n) is used in more than one basic block.
        !           118:    Or -1 if it has not yet been seen so no basic block is known.
        !           119:    This information remains valid for the rest of the compilation
        !           120:    of the current function; it is used to control register allocation.  */
        !           121: 
        !           122: short *reg_basic_block;
        !           123: 
        !           124: /* Indexed by n, gives number of times (REG n) is used or set, each
        !           125:    weighted by its loop-depth.
        !           126:    This information remains valid for the rest of the compilation
        !           127:    of the current function; it is used to control register allocation.  */
        !           128: 
        !           129: short *reg_n_refs;
        !           130: 
        !           131: /* Indexed by n, gives number of times (REG n) is set.
        !           132:    This information remains valid for the rest of the compilation
        !           133:    of the current function; it is used to control register allocation.  */
        !           134: 
        !           135: short *reg_n_sets;
        !           136: 
        !           137: /* Indexed by N, gives number of places register N dies.
        !           138:    This information remains valid for the rest of the compilation
        !           139:    of the current function; it is used to control register allocation.  */
        !           140: 
        !           141: short *reg_n_deaths;
        !           142: 
        !           143: /* Indexed by N, gives 1 if that reg is live across any CALL_INSNs.
        !           144:    This information remains valid for the rest of the compilation
        !           145:    of the current function; it is used to control register allocation.  */
        !           146: 
        !           147: char *reg_crosses_call;
        !           148: 
        !           149: /* Total number of instructions at which (REG n) is live.
        !           150:    The larger this is, the less priority (REG n) gets for
        !           151:    allocation in a real register.
        !           152:    This information remains valid for the rest of the compilation
        !           153:    of the current function; it is used to control register allocation.  */
        !           154: 
        !           155: int *reg_live_length;
        !           156: 
        !           157: /* Element N is the next insn that uses (hard or pseudo) register number N
        !           158:    within the current basic block; or zero, if there is no such insn.
        !           159:    This is valid only during the final backward scan in propagate_block.  */
        !           160: 
        !           161: static rtx *reg_next_use;
        !           162: 
        !           163: /* Size of a regset for the current function,
        !           164:    in (1) bytes and (2) elements.  */
        !           165: 
        !           166: int regset_bytes;
        !           167: int regset_size;
        !           168: 
        !           169: /* Element N is first insn in basic block N.
        !           170:    This info lasts until we finish compiling the function.  */
        !           171: 
        !           172: rtx *basic_block_head;
        !           173: 
        !           174: /* Element N is last insn in basic block N.
        !           175:    This info lasts until we finish compiling the function.  */
        !           176: 
        !           177: rtx *basic_block_end;
        !           178: 
        !           179: /* Element N is a regset describing the registers live
        !           180:    at the start of basic block N.
        !           181:    This info lasts until we finish compiling the function.  */
        !           182: 
        !           183: regset *basic_block_live_at_start;
        !           184: 
        !           185: /* Element N is nonzero if control can drop into basic block N
        !           186:    from the preceding basic block.  Freed after life_analysis.  */
        !           187: 
        !           188: char *basic_block_drops_in;
        !           189: 
        !           190: /* Element N is depth within loops of basic block number N.
        !           191:    Freed after life_analysis.  */
        !           192: 
        !           193: short *basic_block_loop_depth;
        !           194: 
        !           195: /* Element N nonzero if basic block N can actually be reached.
        !           196:    Vector exists only during find_basic_blocks.  */
        !           197: 
        !           198: char *block_live_static;
        !           199: 
        !           200: /* Depth within loops of basic block being scanned for lifetime analysis,
        !           201:    plus one.  This is the weight attached to references to registers.  */
        !           202: 
        !           203: int loop_depth;
        !           204: 
        !           205: /* Forward declarations */
        !           206: static void find_basic_blocks ();
        !           207: static void life_analysis ();
        !           208: static void mark_label_ref ();
        !           209: void allocate_for_life_analysis (); /* Used also in stupid_life_analysis */
        !           210: static void init_regset_vector ();
        !           211: static void propagate_block ();
        !           212: static void mark_set_regs ();
        !           213: static void mark_used_regs ();
        !           214: static int insn_dead_p ();
        !           215: static int try_pre_increment ();
        !           216: static int try_pre_increment_1 ();
        !           217: static rtx find_use_as_address ();
        !           218: 
        !           219: /* Find basic blocks of the current function and perform data flow analysis.
        !           220:    F is the first insn of the function and NREGS the number of register numbers
        !           221:    in use.  */
        !           222: 
        !           223: void
        !           224: flow_analysis (f, nregs, file)
        !           225:      rtx f;
        !           226:      int nregs;
        !           227:      FILE *file;
        !           228: {
        !           229:   register rtx insn;
        !           230:   register int i;
        !           231:   register int max_uid = 0;
        !           232: 
        !           233:   /* Count the basic blocks.  Also find maximum insn uid value used.  */
        !           234: 
        !           235:   {
        !           236:     register RTX_CODE prev_code = JUMP_INSN;
        !           237:     register RTX_CODE code;
        !           238: 
        !           239:     for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
        !           240:       {
        !           241:        code = GET_CODE (insn);
        !           242:        if (INSN_UID (insn) > max_uid)
        !           243:          max_uid = INSN_UID (insn);
        !           244:        if (code == CODE_LABEL
        !           245:            || (prev_code != INSN && prev_code != CALL_INSN
        !           246:                && prev_code != CODE_LABEL
        !           247:                && (code == INSN || code == CALL_INSN || code == JUMP_INSN)))
        !           248:          i++;
        !           249:        if (code != NOTE)
        !           250:          prev_code = code;
        !           251:       }
        !           252:   }
        !           253: 
        !           254:   /* Allocate some tables that last till end of compiling this function
        !           255:      and some needed only in find_basic_blocks and life_analysis.  */
        !           256: 
        !           257:   n_basic_blocks = i;
        !           258:   basic_block_head = (rtx *) oballoc (n_basic_blocks * sizeof (rtx));
        !           259:   basic_block_end = (rtx *) oballoc (n_basic_blocks * sizeof (rtx));
        !           260:   basic_block_drops_in = (char *) alloca (n_basic_blocks);
        !           261:   basic_block_loop_depth = (short *) alloca (n_basic_blocks * sizeof (short));
        !           262:   uid_block_number = (short *) alloca ((max_uid + 1) * sizeof (short));
        !           263: 
        !           264:   find_basic_blocks (f);
        !           265:   life_analysis (f, nregs);
        !           266:   if (file)
        !           267:     dump_flow_info (file);
        !           268: 
        !           269:   basic_block_drops_in = 0;
        !           270:   uid_block_number = 0;
        !           271:   basic_block_loop_depth = 0;
        !           272: }
        !           273: 
        !           274: /* Find all basic blocks of the function whose first insn is F.
        !           275:    Store the correct data in the tables that describe the basic blocks,
        !           276:    set up the chains of references for each CODE_LABEL, and
        !           277:    delete any entire basic blocks that cannot be reached.  */
        !           278: 
        !           279: static void
        !           280: find_basic_blocks (f)
        !           281:      rtx f;
        !           282: {
        !           283:   register rtx insn;
        !           284:   register int i;
        !           285: 
        !           286:   /* Initialize the ref chain of each label to 0.  */
        !           287:   /* Record where all the blocks start and end and their depth in loops.  */
        !           288:   /* For each insn, record the block it is in.  */
        !           289: 
        !           290:   {
        !           291:     register RTX_CODE prev_code = JUMP_INSN;
        !           292:     register RTX_CODE code;
        !           293:     int depth = 1;
        !           294: 
        !           295:     for (insn = f, i = -1; insn; insn = NEXT_INSN (insn))
        !           296:       {
        !           297:        code = GET_CODE (insn);
        !           298:        if (code == NOTE)
        !           299:          {
        !           300:            if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_BEG)
        !           301:              depth++;
        !           302:            else if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_END)
        !           303:              depth--;
        !           304:          }
        !           305:        else if (code == CODE_LABEL
        !           306:                 || (prev_code != INSN && prev_code != CALL_INSN
        !           307:                     && prev_code != CODE_LABEL
        !           308:                     && (code == INSN || code == CALL_INSN || code == JUMP_INSN)))
        !           309:          {
        !           310:            basic_block_head[++i] = insn;
        !           311:            basic_block_end[i] = insn;
        !           312:            basic_block_loop_depth[i] = depth;
        !           313:            if (code == CODE_LABEL)
        !           314:              LABEL_REFS (insn) = insn;
        !           315:          }
        !           316:        else if (code == INSN || code == CALL_INSN || code == JUMP_INSN)
        !           317:          basic_block_end[i] = insn;
        !           318:        BLOCK_NUM (insn) = i;
        !           319:        if (code != NOTE)
        !           320:          prev_code = code;
        !           321:       }
        !           322:   }
        !           323: 
        !           324:   /* Record which basic blocks control can drop in to.  */
        !           325: 
        !           326:   {
        !           327:     register int i;
        !           328:     for (i = 0; i < n_basic_blocks; i++)
        !           329:       {
        !           330:        register rtx insn = PREV_INSN (basic_block_head[i]);
        !           331:        while (insn && GET_CODE (insn) == NOTE)
        !           332:          insn = PREV_INSN (insn);
        !           333:        basic_block_drops_in[i]
        !           334:          = insn && GET_CODE (insn) != BARRIER;
        !           335:       }
        !           336:   }
        !           337: 
        !           338:   /* Now find which basic blocks can actually be reached
        !           339:      and put all jump insns' LABEL_REFS onto the ref-chains
        !           340:      of their target labels.  */
        !           341: 
        !           342:   if (n_basic_blocks > 0)
        !           343:     {
        !           344:       register char *block_live = (char *) alloca (n_basic_blocks);
        !           345:       register char *block_marked = (char *) alloca (n_basic_blocks);
        !           346:       int something_marked = 1;
        !           347: 
        !           348:       /* Initialize with just block 0 reachable and no blocks marked.  */
        !           349: 
        !           350:       bzero (block_live, n_basic_blocks);
        !           351:       bzero (block_marked, n_basic_blocks);
        !           352:       block_live[0] = 1;
        !           353:       block_live_static = block_live;
        !           354: 
        !           355:       /* Pass over all blocks, marking each block that is reachable
        !           356:         and has not yet been marked.
        !           357:         Keep doing this until, in one pass, no blocks have been marked.
        !           358:         Then blocks_live and blocks_marked are identical and correct.
        !           359:         In addition, all jumps actually reachable have been marked.  */
        !           360: 
        !           361:       while (something_marked)
        !           362:        {
        !           363:          something_marked = 0;
        !           364:          for (i = 0; i < n_basic_blocks; i++)
        !           365:            if (block_live[i] && !block_marked[i])
        !           366:              {
        !           367:                block_marked[i] = 1;
        !           368:                something_marked = 1;
        !           369:                if (i + 1 < n_basic_blocks && basic_block_drops_in[i + 1])
        !           370:                  block_live[i + 1] = 1;
        !           371:                insn = basic_block_end[i];
        !           372:                if (GET_CODE (insn) == JUMP_INSN)
        !           373:                  mark_label_ref (PATTERN (insn), insn, 0);
        !           374:              }
        !           375:        }
        !           376: 
        !           377:       /* Now delete the code for any basic blocks that can't be reached.
        !           378:         They can occur because jump_optimize does not recognize
        !           379:         unreachable loops as unreachable.  */
        !           380: 
        !           381:       for (i = 0; i < n_basic_blocks; i++)
        !           382:        if (!block_live[i])
        !           383:          {
        !           384:            insn = basic_block_head[i];
        !           385:            while (1)
        !           386:              {
        !           387:                if (GET_CODE (insn) != NOTE)
        !           388:                  {
        !           389:                    PUT_CODE (insn, NOTE);
        !           390:                    NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
        !           391:                    NOTE_SOURCE_FILE (insn) = 0;
        !           392:                  }
        !           393:                if (insn == basic_block_end[i])
        !           394:                  break;
        !           395:                insn = NEXT_INSN (insn);
        !           396:              }
        !           397:            /* Each time we delete some basic blocks,
        !           398:               see if there is a jump around them that is
        !           399:               being turned into a no-op.  If so, delete it.  */
        !           400: 
        !           401:            if (block_live[i - 1])
        !           402:              {
        !           403:                register int j;
        !           404:                for (j = i; j < n_basic_blocks; j++)
        !           405:                  if (block_live[j])
        !           406:                    {
        !           407:                      insn = basic_block_end[i - 1];
        !           408:                      if (GET_CODE (insn) == JUMP_INSN
        !           409:                          && JUMP_LABEL (insn) != 0
        !           410:                          && BLOCK_NUM (JUMP_LABEL (insn)) == j)
        !           411:                        {
        !           412:                          PUT_CODE (insn, NOTE);
        !           413:                          NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
        !           414:                          NOTE_SOURCE_FILE (insn) = 0;
        !           415:                        }
        !           416:                      break;
        !           417:                    }
        !           418:              }
        !           419:          }
        !           420:     }
        !           421: }
        !           422: 
        !           423: /* Check expression X for label references;
        !           424:    if one is found, add INSN to the label's chain of references.
        !           425: 
        !           426:    CHECKDUP means check for and avoid creating duplicate references
        !           427:    from the same insn.  Such duplicates do no serious harm but
        !           428:    can slow life analysis.  CHECKDUP is set only when duplicates
        !           429:    are likely.  */
        !           430: 
        !           431: static void
        !           432: mark_label_ref (x, insn, checkdup)
        !           433:      rtx x, insn;
        !           434:      int checkdup;
        !           435: {
        !           436:   register RTX_CODE code = GET_CODE (x);
        !           437:   register int i;
        !           438:   register char *fmt;
        !           439: 
        !           440:   if (code == LABEL_REF)
        !           441:     {
        !           442:       register rtx label = XEXP (x, 0);
        !           443:       register rtx y;
        !           444:       if (GET_CODE (label) != CODE_LABEL)
        !           445:        return;
        !           446:       CONTAINING_INSN (x) = insn;
        !           447:       /* if CHECKDUP is set, check for duplicate ref from same insn
        !           448:         and don't insert.  */
        !           449:       if (checkdup)
        !           450:        for (y = LABEL_REFS (label); y != label; y = LABEL_NEXTREF (y))
        !           451:          if (CONTAINING_INSN (y) == insn)
        !           452:            return;
        !           453:       LABEL_NEXTREF (x) = LABEL_REFS (label);
        !           454:       LABEL_REFS (label) = x;
        !           455:       block_live_static[BLOCK_NUM (label)] = 1;
        !           456:       return;
        !           457:     }
        !           458: 
        !           459:   fmt = GET_RTX_FORMAT (code);
        !           460:   for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
        !           461:     {
        !           462:       if (fmt[i] == 'e')
        !           463:        mark_label_ref (XEXP (x, i), insn, 0);
        !           464:       if (fmt[i] == 'E')
        !           465:        {
        !           466:          register int j;
        !           467:          for (j = 0; j < XVECLEN (x, i); j++)
        !           468:            mark_label_ref (XVECEXP (x, i, j), insn, 1);
        !           469:        }
        !           470:     }
        !           471: }
        !           472: 
        !           473: /* Determine the which registers are live at the start of each
        !           474:    basic block of the function whose first insn is F.
        !           475:    NREGS is the number of registers used in F.
        !           476:    We allocate the vector basic_block_live_at_start
        !           477:    and the regsets that it points to, and fill them with the data.
        !           478:    regset_size and regset_bytes are also set here.  */
        !           479: 
        !           480: static void
        !           481: life_analysis (f, nregs)
        !           482:      rtx f;
        !           483:      int nregs;
        !           484: {
        !           485:   register regset tem;
        !           486:   int first_pass;
        !           487:   int changed;
        !           488:   /* For each basic block, a bitmask of regs
        !           489:      live on exit from the block.  */
        !           490:   regset *basic_block_live_at_end;
        !           491:   /* For each basic block, a bitmask of regs
        !           492:      live on entry to a successor-block of this block.
        !           493:      If this does not match basic_block_live_at_end,
        !           494:      that must be updated, and the block must be rescanned.  */
        !           495:   regset *basic_block_new_live_at_end;
        !           496:   /* For each basic block, a bitmask of regs
        !           497:      whose liveness at the end of the basic block
        !           498:      can make a difference in which regs are live on entry to the block.
        !           499:      These are the regs that are set within the basic block,
        !           500:      possibly excluding those that are used after they are set.  */
        !           501:   regset *basic_block_significant;
        !           502:   register int i;
        !           503: 
        !           504:   max_regno = nregs;
        !           505: 
        !           506:   bzero (regs_ever_live, sizeof regs_ever_live);
        !           507: 
        !           508:   /* Allocate and zero out many data structures
        !           509:      that will record the data from lifetime analysis.  */
        !           510: 
        !           511:   allocate_for_life_analysis ();
        !           512: 
        !           513:   reg_next_use = (rtx *) alloca (nregs * sizeof (rtx));
        !           514:   bzero (reg_next_use, nregs * sizeof (rtx));
        !           515: 
        !           516:   /* Set up several regset-vectors used internally within this function.
        !           517:      Their meanings are documented above, with their declarations.  */
        !           518: 
        !           519:   basic_block_live_at_end = (regset *) alloca (n_basic_blocks * sizeof (regset));
        !           520:   tem = (regset) alloca (n_basic_blocks * regset_bytes);
        !           521:   bzero (tem, n_basic_blocks * regset_bytes);
        !           522:   init_regset_vector (basic_block_live_at_end, tem, n_basic_blocks, regset_bytes);
        !           523: 
        !           524:   basic_block_new_live_at_end = (regset *) alloca (n_basic_blocks * sizeof (regset));
        !           525:   tem = (regset) alloca (n_basic_blocks * regset_bytes);
        !           526:   bzero (tem, n_basic_blocks * regset_bytes);
        !           527:   init_regset_vector (basic_block_new_live_at_end, tem, n_basic_blocks, regset_bytes);
        !           528: 
        !           529:   basic_block_significant = (regset *) alloca (n_basic_blocks * sizeof (regset));
        !           530:   tem = (regset) alloca (n_basic_blocks * regset_bytes);
        !           531:   bzero (tem, n_basic_blocks * regset_bytes);
        !           532:   init_regset_vector (basic_block_significant, tem, n_basic_blocks, regset_bytes);
        !           533: 
        !           534:   /* Propagate life info through the basic blocks
        !           535:      around the graph of basic blocks.
        !           536: 
        !           537:      This is a relaxation process: each time a new register
        !           538:      is live at the end of the basic block, we must scan the block
        !           539:      to determine which registers are, as a consequence, live at the beginning
        !           540:      of that block.  These registers must then be marked live at the ends
        !           541:      of all the blocks that can transfer control to that block.
        !           542:      The process continues until it reaches a fixed point.  */
        !           543: 
        !           544:   first_pass = 1;
        !           545:   changed = 1;
        !           546:   while (changed)
        !           547:     {
        !           548:       changed = 0;
        !           549:       for (i = n_basic_blocks - 1; i >= 0; i--)
        !           550:        {
        !           551:          int consider = first_pass;
        !           552:          int must_rescan = first_pass;
        !           553:          register int j;
        !           554: 
        !           555:          /* Set CONSIDER if this block needs thinking about at all
        !           556:             (that is, if the regs live now at the end of it
        !           557:             are not the same as were live at the end of it when
        !           558:             we last thought about it).
        !           559:             Set must_rescan if it needs to be thought about
        !           560:             instruction by instruction (that is, if any additional
        !           561:             reg that is live at the end now but was not live there before
        !           562:             is one of the significant regs of this basic block).  */
        !           563: 
        !           564:          for (j = 0; j < regset_size; j++)
        !           565:            {
        !           566:              register int x = basic_block_new_live_at_end[i][j]
        !           567:                      & ~basic_block_live_at_end[i][j];
        !           568:              if (x)
        !           569:                consider = 1;
        !           570:              if (x & basic_block_significant[i][j])
        !           571:                {
        !           572:                  must_rescan = 1;
        !           573:                  consider = 1;
        !           574:                  break;
        !           575:                }
        !           576:            }
        !           577: 
        !           578:          if (! consider)
        !           579:            continue;
        !           580: 
        !           581:          /* The live_at_start of this block may be changing,
        !           582:             so another pass will be required after this one.  */
        !           583:          changed = 1;
        !           584: 
        !           585:          if (! must_rescan)
        !           586:            {
        !           587:              /* No complete rescan needed;
        !           588:                 just record those variables newly known live at end
        !           589:                 as live at start as well.  */
        !           590:              for (j = 0; j < regset_size; j++)
        !           591:                {
        !           592:                  register int x = basic_block_new_live_at_end[i][j]
        !           593:                        & ~basic_block_live_at_end[i][j];
        !           594:                  basic_block_live_at_start[i][j] |= x;
        !           595:                  basic_block_live_at_end[i][j] |= x;
        !           596:                }
        !           597:            }
        !           598:          else
        !           599:            {
        !           600:              /* Update the basic_block_live_at_start
        !           601:                 by propagation backwards through the block.  */
        !           602:              bcopy (basic_block_new_live_at_end[i],
        !           603:                     basic_block_live_at_end[i], regset_bytes);
        !           604:              bcopy (basic_block_live_at_end[i],
        !           605:                     basic_block_live_at_start[i], regset_bytes);
        !           606:              propagate_block (basic_block_live_at_start[i],
        !           607:                               basic_block_head[i], basic_block_end[i], 0,
        !           608:                               first_pass ? basic_block_significant[i] : 0,
        !           609:                               i);
        !           610:            }
        !           611: 
        !           612:          {
        !           613:            register rtx jump, head;
        !           614:            /* Update the basic_block_new_live_at_end's of the block
        !           615:               that falls through into this one (if any).  */
        !           616:            head = basic_block_head[i];
        !           617:            jump = PREV_INSN (head);
        !           618:            if (basic_block_drops_in[i])
        !           619:              {
        !           620:                register from_block = BLOCK_NUM (jump);
        !           621:                register int j;
        !           622:                for (j = 0; j < regset_size; j++)
        !           623:                  basic_block_new_live_at_end[from_block][j]
        !           624:                    |= basic_block_live_at_start[i][j];
        !           625:              }
        !           626:            /* Update the basic_block_new_live_at_end's of
        !           627:               all the blocks that jump to this one.  */
        !           628:            if (GET_CODE (head) == CODE_LABEL)
        !           629:              for (jump = LABEL_REFS (head);
        !           630:                   jump != head;
        !           631:                   jump = LABEL_NEXTREF (jump))
        !           632:                {
        !           633:                  register from_block = BLOCK_NUM (CONTAINING_INSN (jump));
        !           634:                  register int j;
        !           635:                  for (j = 0; j < regset_size; j++)
        !           636:                    basic_block_new_live_at_end[from_block][j]
        !           637:                      |= basic_block_live_at_start[i][j];
        !           638:                }
        !           639:          }
        !           640:        }
        !           641:       first_pass = 0;
        !           642:     }
        !           643: 
        !           644:   /* Now the life information is accurate.
        !           645:      Make one more pass over each basic block
        !           646:      to delete dead stores, create autoincrement addressing
        !           647:      and record how many times each register is used, is set, or dies.
        !           648: 
        !           649:      To save time, we operate directly in basic_block_live_at_end[i],
        !           650:      thus destroying it (in fact, converting it into a copy of
        !           651:      basic_block_live_at_start[i]).  This is ok now because
        !           652:      basic_block_live_at_end[i] is no longer used past this point.  */
        !           653: 
        !           654:   for (i = 0; i < n_basic_blocks; i++)
        !           655:     {
        !           656:       propagate_block (basic_block_live_at_end[i],
        !           657:                       basic_block_head[i], basic_block_end[i], 1, 0, i);
        !           658:     }
        !           659: }
        !           660: 
        !           661: /* Subroutines of life analysis.  */
        !           662: 
        !           663: /* Allocate the permanent data structures that represent the results
        !           664:    of life analysis.  Not static since used also for stupid life analysis.  */
        !           665: 
        !           666: void
        !           667: allocate_for_life_analysis ()
        !           668: {
        !           669:   register int i;
        !           670:   register regset tem;
        !           671: 
        !           672:   regset_size = ((max_regno + REGSET_ELT_BITS - 1) / REGSET_ELT_BITS);
        !           673:   regset_bytes = regset_size * sizeof (*(regset)0);
        !           674: 
        !           675:   reg_n_refs = (short *) oballoc (max_regno * sizeof (short));
        !           676:   bzero (reg_n_refs, max_regno * sizeof (short));
        !           677: 
        !           678:   reg_n_sets = (short *) oballoc (max_regno * sizeof (short));
        !           679:   bzero (reg_n_sets, max_regno * sizeof (short));
        !           680: 
        !           681:   reg_n_deaths = (short *) oballoc (max_regno * sizeof (short));
        !           682:   bzero (reg_n_deaths, max_regno * sizeof (short));
        !           683: 
        !           684:   reg_live_length = (int *) oballoc (max_regno * sizeof (int));
        !           685:   bzero (reg_live_length, max_regno * sizeof (int));
        !           686: 
        !           687:   reg_crosses_call = (char *) oballoc (max_regno);
        !           688:   bzero (reg_crosses_call, max_regno);
        !           689: 
        !           690:   reg_basic_block = (short *) oballoc (max_regno * sizeof (short));
        !           691:   for (i = 0; i < max_regno; i++)
        !           692:     reg_basic_block[i] = -1;
        !           693: 
        !           694:   basic_block_live_at_start = (regset *) oballoc (n_basic_blocks * sizeof (regset));
        !           695:   tem = (regset) oballoc (n_basic_blocks * regset_bytes);
        !           696:   bzero (tem, n_basic_blocks * regset_bytes);
        !           697:   init_regset_vector (basic_block_live_at_start, tem, n_basic_blocks, regset_bytes);
        !           698: }
        !           699: 
        !           700: /* Make each element of VECTOR point at a regset,
        !           701:    taking the space for all those regsets from SPACE.
        !           702:    SPACE is of type regset, but it is really as long as NELTS regsets.
        !           703:    BYTES_PER_ELT is the number of bytes in one regset.  */
        !           704: 
        !           705: static void
        !           706: init_regset_vector (vector, space, nelts, bytes_per_elt)
        !           707:      regset *vector;
        !           708:      regset space;
        !           709:      int nelts;
        !           710:      int bytes_per_elt;
        !           711: {
        !           712:   register int i;
        !           713:   register regset p = space;
        !           714: 
        !           715:   for (i = 0; i < nelts; i++)
        !           716:     {
        !           717:       vector[i] = p;
        !           718:       p += bytes_per_elt / sizeof (*p);
        !           719:     }
        !           720: }
        !           721: 
        !           722: /* Compute the registers live at the beginning of a basic block
        !           723:    from those live at the end.
        !           724: 
        !           725:    When called, OLD contains those live at the end.
        !           726:    On return, it contains those live at the beginning.
        !           727:    FIRST and LAST are the first and last insns of the basic block.
        !           728: 
        !           729:    FINAL is nonzero if we are doing the final pass which is not
        !           730:    for computing the life info (since that has already been done)
        !           731:    but for acting on it.  On this pass, we delete dead stores,
        !           732:    set up the logical links and dead-variables lists of instructions,
        !           733:    and merge instructions for autoincrement and autodecrement addresses.
        !           734: 
        !           735:    SIGNIFICANT is nonzero only the first time for each basic block.
        !           736:    If it is nonzero, it points to a regset in which we store
        !           737:    a 1 for each register that is set within the block.
        !           738: 
        !           739:    BNUM is the number of the basic block.  */
        !           740: 
        !           741: static void
        !           742: propagate_block (old, first, last, final, significant, bnum)
        !           743:      register regset old;
        !           744:      rtx first;
        !           745:      rtx last;
        !           746:      int final;
        !           747:      regset significant;
        !           748:      int bnum;
        !           749: {
        !           750:   register rtx insn;
        !           751:   rtx prev;
        !           752:   regset live;
        !           753:   regset dead;
        !           754: 
        !           755:   /* The following variables are used only if FINAL is nonzero.  */
        !           756:   /* This vector gets one element for each reg that has been live
        !           757:      at any point in the basic block that has been scanned so far.
        !           758:      SOMETIMES_MAX says how many elements are in use so far.
        !           759:      In each element, OFFSET is the byte-number within a regset
        !           760:      for the register described by the element, and BIT is a mask
        !           761:      for that register's bit within the byte.  */
        !           762:   register struct foo { short offset; short bit; } *regs_sometimes_live;
        !           763:   int sometimes_max = 0;
        !           764:   /* This regset has 1 for each reg that we have seen live so far.
        !           765:      It and REGS_SOMETIMES_LIVE are updated together.  */
        !           766:   regset maxlive;
        !           767: 
        !           768:   loop_depth = basic_block_loop_depth[bnum];
        !           769: 
        !           770:   dead = (regset) alloca (regset_bytes);
        !           771:   live = (regset) alloca (regset_bytes);
        !           772: 
        !           773:   if (final)
        !           774:     {
        !           775:       register int i, offset, bit;
        !           776: 
        !           777:       maxlive = (regset) alloca (regset_bytes);
        !           778:       bcopy (old, maxlive, regset_bytes);
        !           779:       regs_sometimes_live
        !           780:        = (struct foo *) alloca (max_regno * sizeof (struct foo));
        !           781: 
        !           782:       /* Process the regs live at the end of the block.
        !           783:         Enter them in MAXLIVE and REGS_SOMETIMES_LIVE.
        !           784:         Also mark them as not local to any one basic block.  */
        !           785: 
        !           786:       for (offset = 0, i = 0; offset < regset_size; offset++)
        !           787:        for (bit = 1; bit; bit <<= 1, i++)
        !           788:          {
        !           789:            if (i == max_regno)
        !           790:              break;
        !           791:            if (old[offset] & bit)
        !           792:              {
        !           793:                reg_basic_block[i] = -2;
        !           794:                regs_sometimes_live[sometimes_max].offset = offset;
        !           795:                regs_sometimes_live[sometimes_max].bit = i % REGSET_ELT_BITS;
        !           796:                sometimes_max++;
        !           797:              }
        !           798:          }
        !           799:     }
        !           800: 
        !           801:   /* Scan the block an insn at a time from end to beginning.  */
        !           802: 
        !           803:   for (insn = last; ; insn = prev)
        !           804:     {
        !           805:       prev = PREV_INSN (insn);
        !           806:       if (final && GET_CODE (insn) == CALL_INSN)
        !           807:        {
        !           808:          /* Any regs live at the time of a call instruction
        !           809:             must not go in a register clobbered by calls.
        !           810:             Find all regs now live and record this for them.  */
        !           811:             
        !           812:          register int i;
        !           813:          register struct foo *p = regs_sometimes_live;
        !           814: 
        !           815:          for (i = 0; i < sometimes_max; i++, p++)
        !           816:            {
        !           817:              if (old[p->offset]
        !           818:                  & (1 << p->bit))
        !           819:                reg_crosses_call[p->offset * REGSET_ELT_BITS + p->bit] = 1;
        !           820:            }
        !           821:        }
        !           822: 
        !           823:       /* Update the life-status of regs for this insn.
        !           824:         First DEAD gets which regs are set in this insn
        !           825:         then LIVE gets which regs are used in this insn.
        !           826:         Then the regs live before the insn
        !           827:         are those live after, with DEAD regs turned off,
        !           828:         and then LIVE regs turned on.  */
        !           829: 
        !           830:       if (GET_CODE (insn) == INSN
        !           831:          || GET_CODE (insn) == JUMP_INSN
        !           832:          || GET_CODE (insn) == CALL_INSN)
        !           833:        {
        !           834:          register int i;
        !           835:          for (i = 0; i < regset_size; i++)
        !           836:            {
        !           837:              dead[i] = 0;      /* Faster than bzero here */
        !           838:              live[i] = 0;      /* since regset_size is usually small */
        !           839:            }
        !           840:          /* If an instruction consists of just dead store(s) on final pass,
        !           841:             "delete" it by turning it into a NOTE of type NOTE_INSN_DELETED.
        !           842:             We could really delete it with delete_insn, but that
        !           843:             can cause trouble for first or last insn in a basic block.  */
        !           844:          if (final && insn_dead_p (PATTERN (insn), old))
        !           845:            {
        !           846:              PUT_CODE (insn, NOTE);
        !           847:              NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
        !           848:              NOTE_SOURCE_FILE (insn) = 0;
        !           849:              goto flushed;
        !           850:            }
        !           851:          else
        !           852:            {
        !           853: /* Check for an opportunity to do predecrement or preincrement addressing.  */
        !           854: #if defined (HAVE_PRE_INCREMENT) || defined (HAVE_PRE_DECREMENT)
        !           855:              register rtx x = PATTERN (insn);
        !           856:              /* Does this instruction increment or decrement a register?  */
        !           857:              if (final && GET_CODE (x) == SET
        !           858:                  && GET_CODE (SET_DEST (x)) == REG
        !           859:                  && (GET_CODE (SET_SRC (x)) == PLUS
        !           860:                      || GET_CODE (SET_SRC (x)) == MINUS)
        !           861:                  && XEXP (SET_SRC (x), 0) == SET_DEST (x)
        !           862:                  && GET_CODE (XEXP (SET_SRC (x), 1)) == CONST_INT
        !           863:                  /* Ok, look for a following memory ref we can combine with.
        !           864:                     If one is found, change the memory ref to a PRE_INC
        !           865:                     or PRE_DEC, cancel this insn, and return 1.
        !           866:                     Return 0 if nothing has been done.  */
        !           867:                  && try_pre_increment_1 (insn))
        !           868:                goto flushed;
        !           869: #endif /* HAVE_PRE_INCREMENT or HAVE_PRE_DECREMENT */
        !           870: 
        !           871:              /* LIVE gets the registers used in INSN; DEAD gets those set by it.  */
        !           872: 
        !           873:              /* A function call implicitly sets the function-value register */
        !           874:              if (GET_CODE (insn) == CALL_INSN)
        !           875:                dead[FUNCTION_VALUE_REGNUM / REGSET_ELT_BITS]
        !           876:                  |= 1 << (FUNCTION_VALUE_REGNUM % REGSET_ELT_BITS);
        !           877:              mark_set_regs (old, dead, PATTERN (insn), final ? insn : 0,
        !           878:                             significant);
        !           879:              mark_used_regs (old, live, PATTERN (insn), final ? insn : 0);
        !           880: 
        !           881:              /* Update OLD for the registers used or set.  */
        !           882:              for (i = 0; i < regset_size; i++)
        !           883:                {
        !           884:                  old[i] &= ~dead[i];
        !           885:                  old[i] |= live[i];
        !           886:                }
        !           887: 
        !           888:              /* On final pass, add any additional sometimes-live regs
        !           889:                 into MAXLIVE and REGS_SOMETIMES_LIVE.
        !           890:                 Also update counts of how many insns each reg is live at.  */
        !           891: 
        !           892:              if (final)
        !           893:                {
        !           894:                  register int diff;
        !           895: 
        !           896:                  for (i = 0; i < regset_size; i++)
        !           897:                    if (diff = live[i] & ~maxlive[i])
        !           898:                      {
        !           899:                        register int regno;
        !           900:                        maxlive[i] |= diff;
        !           901:                        for (regno = 0; diff && regno < REGSET_ELT_BITS; regno++)
        !           902:                          if (diff & (1 << regno))
        !           903:                            {
        !           904:                              regs_sometimes_live[sometimes_max].offset = i;
        !           905:                              regs_sometimes_live[sometimes_max].bit = regno;
        !           906:                              diff &= ~ (1 << regno);
        !           907:                              sometimes_max++;
        !           908:                            }
        !           909:                      }
        !           910: 
        !           911:                  {
        !           912:                    register struct foo *p = regs_sometimes_live;
        !           913:                    for (i = 0; i < sometimes_max; i++, p++)
        !           914:                      {
        !           915:                        if (old[p->offset]
        !           916:                            & (1 << p->bit))
        !           917:                          reg_live_length[p->offset * REGSET_ELT_BITS + p->bit]++;
        !           918:                      }
        !           919:                  }
        !           920:                  /* This probably gets set to 1 in various places;
        !           921:                     make sure it is 0.  */
        !           922:                  reg_crosses_call[FUNCTION_VALUE_REGNUM] = 0;
        !           923:                }
        !           924:            }
        !           925:        flushed: ;
        !           926:        }
        !           927:       if (insn == first)
        !           928:        break;
        !           929:     }
        !           930: }
        !           931: 
        !           932: /* Return 1 if X (the body of an insn, or part of it) is just dead stores
        !           933:    (SET expressions whose destinations are registers dead after the insn).
        !           934:    NEEDED is the regset that says which regs are alive after the insn.  */
        !           935: 
        !           936: static int
        !           937: insn_dead_p (x, needed)
        !           938:      rtx x;
        !           939:      regset needed;
        !           940: {
        !           941:   register RTX_CODE code = GET_CODE (x);
        !           942:   /* Make sure insns to set the stack pointer are never deleted.  */
        !           943:   needed[STACK_POINTER_REGNUM / REGSET_ELT_BITS]
        !           944:     |= 1 << (STACK_POINTER_REGNUM % REGSET_ELT_BITS);
        !           945:   if (code == SET && GET_CODE (SET_DEST (x)) == REG)
        !           946:     {
        !           947:       register int regno = REGNO (SET_DEST (x));
        !           948:       register int offset = regno / REGSET_ELT_BITS;
        !           949:       register int bit = 1 << (regno % REGSET_ELT_BITS);
        !           950:       return (needed[offset] & bit) == 0;
        !           951:     }
        !           952:   if (code == PARALLEL)
        !           953:     {
        !           954:       register int i = XVECLEN (x, 0);
        !           955:       for (i--; i >= 0; i--)
        !           956:        if (!insn_dead_p (XVECEXP (x, 0, i), needed))
        !           957:          return 0;
        !           958:       return 1;
        !           959:     }
        !           960:   return 0;
        !           961: }
        !           962: 
        !           963: /* Return nonzero if register number REGNO is marked as "dying" in INSN's
        !           964:    REG_NOTES list.  */
        !           965: 
        !           966: static int
        !           967: flow_deadp (regno, insn)
        !           968:      int regno;
        !           969:      rtx insn;
        !           970: {
        !           971:   register rtx link;
        !           972:   for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
        !           973:     if (XEXP (link, 0)
        !           974:        && (enum reg_note) GET_MODE (link) == REG_DEAD
        !           975:        && regno == REGNO (XEXP (link, 0)))
        !           976:       return 1;
        !           977:   return 0;
        !           978: }
        !           979: 
        !           980: /* Process the registers that are set within X.
        !           981:    Their bits are set to 1 in the regset DEAD,
        !           982:    because they are dead prior to this insn.
        !           983: 
        !           984:    If INSN is nonzero, it is the insn being processed
        !           985:    and the fact that it is nonzero implies this is the FINAL pass
        !           986:    in propagate_block.  In this case, various info about register
        !           987:    usage is stored, LOG_LINKS fields of insns are set up.  */
        !           988: 
        !           989: static void mark_set_1 ();
        !           990: 
        !           991: static void
        !           992: mark_set_regs (needed, dead, x, insn, significant)
        !           993:      regset needed;
        !           994:      regset dead;
        !           995:      rtx x;
        !           996:      rtx insn;
        !           997:      regset significant;
        !           998: {
        !           999:   register RTX_CODE code = GET_CODE (x);
        !          1000: 
        !          1001:   if (code == SET || code == CLOBBER)
        !          1002:     mark_set_1 (needed, dead, x, insn, significant);
        !          1003:   else if (code == PARALLEL)
        !          1004:     {
        !          1005:       register int i;
        !          1006:       for (i = XVECLEN (x, 0) - 1; i >= 0; i--)
        !          1007:        {
        !          1008:          code = GET_CODE (XVECEXP (x, 0, i));
        !          1009:          if (code == SET || code == CLOBBER)
        !          1010:            mark_set_1 (needed, dead, XVECEXP (x, 0, i), insn, significant);
        !          1011:        }
        !          1012:     }
        !          1013: }
        !          1014: 
        !          1015: /* Process a single SET rtx, X.  */
        !          1016: 
        !          1017: static void
        !          1018: mark_set_1 (needed, dead, x, insn, significant)
        !          1019:      regset needed;
        !          1020:      regset dead;
        !          1021:      rtx x;
        !          1022:      rtx insn;
        !          1023:      regset significant;
        !          1024: {
        !          1025:   register int regno;
        !          1026:   register rtx reg = SET_DEST (x);
        !          1027: 
        !          1028:   if (GET_CODE (reg) == SUBREG)
        !          1029:     {
        !          1030:       /* Modifying just one hardware register
        !          1031:         of a multi-register value does not count as "setting"
        !          1032:         for live-dead analysis.  Parts of the previous value
        !          1033:         might still be significant below this insn.  */
        !          1034:       if (REG_SIZE (SUBREG_REG (reg)) > REG_SIZE (reg))
        !          1035:        return;
        !          1036: 
        !          1037:       reg = SUBREG_REG (reg);
        !          1038:     }
        !          1039: 
        !          1040:   if (GET_CODE (reg) == REG
        !          1041:       && (regno = REGNO (reg), regno != FRAME_POINTER_REGNUM)
        !          1042:       && regno != ARG_POINTER_REGNUM && regno != STACK_POINTER_REGNUM)
        !          1043:     {
        !          1044:       register int offset = regno / REGSET_ELT_BITS;
        !          1045:       register int bit = 1 << (regno % REGSET_ELT_BITS);
        !          1046:       /* Mark the reg being set as dead before this insn.  */
        !          1047:       dead[offset] |= bit;
        !          1048:       /* Mark it as a significant register for this basic block.  */
        !          1049:       if (significant)
        !          1050:        significant[offset] |= bit;
        !          1051:       /* Additional data to record if this is the final pass.  */
        !          1052:       if (insn)
        !          1053:        {
        !          1054:          register rtx y = reg_next_use[regno];
        !          1055:          register int blocknum = BLOCK_NUM (insn);
        !          1056: 
        !          1057:          /* If this is a hard reg, record this function uses the reg.  */
        !          1058: 
        !          1059:          if (regno < FIRST_PSEUDO_REGISTER)
        !          1060:            {
        !          1061:              register int i;
        !          1062:              i = HARD_REGNO_NREGS (regno, GET_MODE (reg));
        !          1063:              do
        !          1064:                regs_ever_live[regno + --i] = 1;
        !          1065:              while (i > 0);
        !          1066:            }
        !          1067: 
        !          1068:          /* Keep track of which basic blocks each reg appears in.  */
        !          1069: 
        !          1070:          if (reg_basic_block[regno] == -1)
        !          1071:            reg_basic_block[regno] = blocknum;
        !          1072:          else if (reg_basic_block[regno] != blocknum)
        !          1073:            reg_basic_block[regno] = -2;
        !          1074: 
        !          1075:          /* Count (weighted) references, stores, etc.  */
        !          1076:          reg_n_refs[regno] += loop_depth;
        !          1077:          reg_n_sets[regno]++;
        !          1078:          /* The insns where a reg is live are normally counted elsewhere,
        !          1079:             but we want the count to include the insn where the reg is set,
        !          1080:             and the normal counting mechanism would not count it.  */
        !          1081:          reg_live_length[regno]++;
        !          1082:          if (needed[offset] & bit)
        !          1083:            {
        !          1084:              /* Make a logical link from the next following insn
        !          1085:                 that uses this register, back to this insn.
        !          1086:                 The following insns have already been processed.  */
        !          1087:              if (y && (BLOCK_NUM (y) == blocknum))
        !          1088:                LOG_LINKS (y)
        !          1089:                  = gen_rtx (INSN_LIST, VOIDmode, insn, LOG_LINKS (y));
        !          1090:            }
        !          1091:          else
        !          1092:            {
        !          1093:              /* Note that dead stores have already been deleted when possible
        !          1094:                 If we get here, we have found a dead store that cannot
        !          1095:                 be eliminated (because the same insn does something useful).
        !          1096:                 Indicate this by marking the reg being set as dying here.  */
        !          1097:              REG_NOTES (insn)
        !          1098:                = gen_rtx (EXPR_LIST, REG_DEAD,
        !          1099:                           reg, REG_NOTES (insn));
        !          1100:            }
        !          1101:        }
        !          1102:     }
        !          1103: }
        !          1104: 
        !          1105: /* Scan expression X and store a 1-bit in LIVE for each reg it uses.
        !          1106:    This is done assuming the registers needed from X
        !          1107:    are those that have 1-bits in NEEDED.
        !          1108: 
        !          1109:    On the final pass, INSN is the containing instruction.  */
        !          1110: 
        !          1111: static void
        !          1112: mark_used_regs (needed, live, x, insn)
        !          1113:      regset needed;
        !          1114:      regset live;
        !          1115:      rtx x;
        !          1116:      rtx insn;
        !          1117: {
        !          1118:   register RTX_CODE code;
        !          1119:   register int regno;
        !          1120: 
        !          1121:  retry:
        !          1122:   code = GET_CODE (x);
        !          1123:   switch (code)
        !          1124:     {
        !          1125:     case LABEL_REF:
        !          1126:     case SYMBOL_REF:
        !          1127:     case CONST_INT:
        !          1128:     case CONST:
        !          1129:     case CC0:
        !          1130:     case PC:
        !          1131:     case CLOBBER:
        !          1132:       return;
        !          1133: 
        !          1134: #if defined (HAVE_POST_INCREMENT) || defined (HAVE_POST_DECREMENT)
        !          1135:     case MEM:
        !          1136:       /* Here we detect use of an index register which might
        !          1137:         be good for postincrement or postdecrement.  */
        !          1138:       if (insn)
        !          1139:        {
        !          1140:          rtx addr = XEXP (x, 0);
        !          1141:          register int size = GET_MODE_SIZE (GET_MODE (x));
        !          1142: 
        !          1143:          if (GET_CODE (addr) == REG)
        !          1144:            {
        !          1145:              register rtx y;
        !          1146:              regno = REGNO (addr);
        !          1147:              /* Is the next use an increment that might make auto-increment? */
        !          1148:              y = reg_next_use[regno];
        !          1149:              if (y && GET_CODE (PATTERN (y)) == SET
        !          1150:                  && BLOCK_NUM (y) == BLOCK_NUM (insn)
        !          1151:                  && SET_DEST (PATTERN (y)) == addr
        !          1152:                  /* Can't add side effects to jumps; if reg is spilled and
        !          1153:                     reloaded, there's no way to store back the altered value.  */
        !          1154:                  && GET_CODE (insn) != JUMP_INSN
        !          1155:                  && (y = SET_SRC (PATTERN (y)),
        !          1156:                      (0
        !          1157: #ifdef HAVE_POST_INCREMENT
        !          1158:                       || GET_CODE (y) == PLUS
        !          1159: #endif
        !          1160: #ifdef HAVE_POST_DECREMENT
        !          1161:                       || GET_CODE (y) == MINUS
        !          1162: #endif
        !          1163:                       )
        !          1164:                      && XEXP (y, 0) == addr
        !          1165:                      && GET_CODE (XEXP (y, 1)) == CONST_INT
        !          1166:                      && INTVAL (XEXP (y, 1)) == size))
        !          1167:                {
        !          1168:                  rtx use = find_use_as_address (PATTERN (insn), addr);
        !          1169: 
        !          1170:                  /* Make sure this register appears only once in this insn.  */
        !          1171:                  if (use != 0 && use != (rtx) 1)
        !          1172:                    {
        !          1173:                      /* We have found a suitable auto-increment:
        !          1174:                         do POST_INC around the register here,
        !          1175:                         and patch out the increment instruction that follows. */
        !          1176:                      XEXP (x, 0)
        !          1177:                        = gen_rtx (GET_CODE (y) == PLUS ? POST_INC : POST_DEC,
        !          1178:                                   Pmode, addr);
        !          1179:                      /* Record that this insn has an implicit side effect.  */
        !          1180:                      REG_NOTES (insn)
        !          1181:                        = gen_rtx (EXPR_LIST, REG_INC, addr, REG_NOTES (insn));
        !          1182: 
        !          1183:                      y = reg_next_use[regno];
        !          1184:                      PUT_CODE (y, NOTE);
        !          1185:                      NOTE_LINE_NUMBER (y) = NOTE_INSN_DELETED;
        !          1186:                      NOTE_SOURCE_FILE (y) = 0;
        !          1187:                      /* Count a reference to this reg for the increment
        !          1188:                         insn we are deleting.  When a reg is incremented.
        !          1189:                         spilling it is worse, so we want to make that
        !          1190:                         less likely.  */
        !          1191:                      reg_n_refs[regno] += loop_depth;
        !          1192:                    }
        !          1193:                }
        !          1194:            }
        !          1195:        }
        !          1196:       break;
        !          1197: #endif /* HAVE_POST_INCREMENT or HAVE_POST_DECREMENT */
        !          1198: 
        !          1199:     case REG:
        !          1200:       /* See a register other than being set
        !          1201:         => mark it as needed.  */
        !          1202: 
        !          1203:       regno = REGNO (x);
        !          1204:       if (regno != FRAME_POINTER_REGNUM
        !          1205:          && regno != ARG_POINTER_REGNUM && regno != STACK_POINTER_REGNUM)
        !          1206:        {
        !          1207:          register int offset = regno / REGSET_ELT_BITS;
        !          1208:          register int bit = 1 << (regno % REGSET_ELT_BITS);
        !          1209:          live[offset] |= bit;
        !          1210:          if (insn)
        !          1211:            {
        !          1212:              register int blocknum = BLOCK_NUM (insn);
        !          1213: 
        !          1214:              /* If a hard reg is being used,
        !          1215:                 record that this function does use it.  */
        !          1216: 
        !          1217:              if (regno < FIRST_PSEUDO_REGISTER)
        !          1218:                {
        !          1219:                  register int i;
        !          1220:                  i = HARD_REGNO_NREGS (regno, GET_MODE (x));
        !          1221:                  do
        !          1222:                    regs_ever_live[regno + --i] = 1;
        !          1223:                  while (i > 0);
        !          1224:                }
        !          1225: 
        !          1226:              /* Keep track of which basic block each reg appears in.  */
        !          1227: 
        !          1228:              if (reg_basic_block[regno] == -1)
        !          1229:                reg_basic_block[regno] = blocknum;
        !          1230:              else if (reg_basic_block[regno] != blocknum)
        !          1231:                reg_basic_block[regno] = -2;
        !          1232: 
        !          1233:              /* Record where each reg is used
        !          1234:                 so when the reg is set we know the next insn that uses it.  */
        !          1235: 
        !          1236:              reg_next_use[regno] = insn;
        !          1237: 
        !          1238:              /* Count (weighted) number of uses of each reg.  */
        !          1239: 
        !          1240:              reg_n_refs[regno] += loop_depth;
        !          1241: 
        !          1242:              /* Record and count the insns in which a reg dies.
        !          1243:                 If it is used in this insn and was dead below the insn
        !          1244:                 then it dies in this insn.  */
        !          1245: 
        !          1246:              if (!(needed[offset] & bit) && !flow_deadp (regno, insn))
        !          1247:                {
        !          1248:                  REG_NOTES (insn)
        !          1249:                    = gen_rtx (EXPR_LIST, REG_DEAD, x, REG_NOTES (insn));
        !          1250:                  reg_n_deaths[regno]++;
        !          1251:                }
        !          1252:            }
        !          1253:        }
        !          1254:       return;
        !          1255: 
        !          1256:     case SET:
        !          1257:       {
        !          1258:        register rtx reg = SET_DEST (x);
        !          1259: 
        !          1260:        /* Modifying just one hardware register
        !          1261:           of a multi-register value does not count as "setting"
        !          1262:           for live-dead analysis.  It is more like a reference.
        !          1263:           But storing in a single register with an alternate mode
        !          1264:           is storing in the register.  */
        !          1265:        if (GET_CODE (reg) == SUBREG
        !          1266:            && !(REG_SIZE (SUBREG_REG (reg)) > REG_SIZE (reg)))
        !          1267:          reg = SUBREG_REG (reg);
        !          1268: 
        !          1269:        /* If this is a store into a register,
        !          1270:           recursively scan the only value being stored,
        !          1271:           and only if the register's value is live after this insn.
        !          1272:           If the value being computed here would never be used
        !          1273:           then the values it uses don't need to be computed either.  */
        !          1274: 
        !          1275:        if (GET_CODE (reg) == REG
        !          1276:            && (regno = REGNO (reg), regno != FRAME_POINTER_REGNUM)
        !          1277:            && regno != ARG_POINTER_REGNUM && regno != STACK_POINTER_REGNUM)
        !          1278:          {
        !          1279:            register int offset = regno / REGSET_ELT_BITS;
        !          1280:            register int bit = 1 << (regno % REGSET_ELT_BITS);
        !          1281:            if (needed[offset] & bit)
        !          1282:              mark_used_regs (needed, live, XEXP (x, 1), insn);
        !          1283:            return;
        !          1284:          }
        !          1285:       }
        !          1286:       break;
        !          1287:     }
        !          1288: 
        !          1289:   /* Recursively scan the operands of this expression.  */
        !          1290: 
        !          1291:   {
        !          1292:     register char *fmt = GET_RTX_FORMAT (code);
        !          1293:     register int i;
        !          1294:     
        !          1295:     for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
        !          1296:       {
        !          1297:        if (fmt[i] == 'e')
        !          1298:          {
        !          1299:            /* Tail recursive case: save a function call level.  */
        !          1300:            if (i == 0)
        !          1301:              {
        !          1302:                x = XEXP (x, 0);
        !          1303:                goto retry;
        !          1304:              }
        !          1305:            mark_used_regs (needed, live, XEXP (x, i), insn);
        !          1306:          }
        !          1307:        if (fmt[i] == 'E')
        !          1308:          {
        !          1309:            register int j;
        !          1310:            for (j = 0; j < XVECLEN (x, i); j++)
        !          1311:              mark_used_regs (needed, live, XVECEXP (x, i, j), insn);
        !          1312:          }
        !          1313:       }
        !          1314:   }
        !          1315: }
        !          1316: 
        !          1317: #if defined (HAVE_PRE_INCREMENT) || defined (HAVE_PRE_DECREMENT)
        !          1318: 
        !          1319: static int
        !          1320: try_pre_increment_1 (insn)
        !          1321:      rtx insn;
        !          1322: {
        !          1323:   /* Find the next use of this reg.  If in same basic block,
        !          1324:      make it do pre-increment or pre-decrement if appropriate.  */
        !          1325:   rtx x = PATTERN (insn);
        !          1326:   int amount = ((GET_CODE (SET_SRC (x)) == PLUS ? 1 : -1)
        !          1327:                * INTVAL (XEXP (SET_SRC (x), 1)));
        !          1328:   int regno = REGNO (SET_DEST (x));
        !          1329:   rtx y = reg_next_use[regno];
        !          1330:   if (y != 0
        !          1331:       && BLOCK_NUM (y) == BLOCK_NUM (insn)
        !          1332:       && try_pre_increment (y, SET_DEST (PATTERN (insn)),
        !          1333:                            amount))
        !          1334:     {
        !          1335:       /* We have found a suitable auto-increment
        !          1336:         and already changed insn Y to do it.
        !          1337:         So flush this increment-instruction.  */
        !          1338:       PUT_CODE (insn, NOTE);
        !          1339:       NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
        !          1340:       NOTE_SOURCE_FILE (insn) = 0;
        !          1341:       /* Count a reference to this reg for the increment
        !          1342:         insn we are deleting.  When a reg is incremented.
        !          1343:         spilling it is worse, so we want to make that
        !          1344:         less likely.  */
        !          1345:       reg_n_refs[regno] += loop_depth;
        !          1346:       return 1;
        !          1347:     }
        !          1348:   return 0;
        !          1349: }
        !          1350: 
        !          1351: /* Try to change INSN so that it does pre-increment or pre-decrement
        !          1352:    addressing on register REG in order to add AMOUNT to REG.
        !          1353:    AMOUNT is negative for pre-decrement.
        !          1354:    Returns 1 if the change could be made.
        !          1355:    This checks all about the validity of the result of modifying INSN.  */
        !          1356: 
        !          1357: static int
        !          1358: try_pre_increment (insn, reg, amount)
        !          1359:      rtx insn, reg;
        !          1360:      int amount;
        !          1361: {
        !          1362:   register rtx use;
        !          1363: 
        !          1364: #ifndef HAVE_PRE_INCREMENT
        !          1365: #ifndef HAVE_PRE_DECREMENT
        !          1366:   return 0;
        !          1367: #else
        !          1368:   if (amount > 0)
        !          1369:     return 0;
        !          1370: #endif
        !          1371: #endif
        !          1372: 
        !          1373: #ifndef HAVE_PRE_DECREMENT
        !          1374:   if (amount < 0)
        !          1375:     return 0;
        !          1376: #endif
        !          1377: 
        !          1378:   /* It is not safe to add a side effect to a jump insn
        !          1379:      because if the incremented register is spilled and must be reloaded
        !          1380:      there would be no way to store the incremented value back in memory.  */
        !          1381: 
        !          1382:   if (GET_CODE (insn) == JUMP_INSN)
        !          1383:     return 0;
        !          1384: 
        !          1385:   use = find_use_as_address (PATTERN (insn), reg);
        !          1386: 
        !          1387:   if (use == 0 || use == (rtx) 1)
        !          1388:     return 0;
        !          1389: 
        !          1390:   if (GET_MODE_SIZE (GET_MODE (use)) != (amount > 0 ? amount : - amount))
        !          1391:     return 0;
        !          1392: 
        !          1393:   XEXP (use, 0) = gen_rtx (amount > 0 ? PRE_INC : PRE_DEC,
        !          1394:                           Pmode, reg);
        !          1395: 
        !          1396:   /* Record that this insn now has an implicit side effect on X.  */
        !          1397:   REG_NOTES (insn) = gen_rtx (EXPR_LIST, REG_INC, reg, REG_NOTES (insn));
        !          1398:   return 1;
        !          1399: }
        !          1400: 
        !          1401: /* Find the place in the rtx X where REG is used as a memory address.
        !          1402:    Return the MEM rtx that so uses it.
        !          1403:    If REG does not appear, return 0.
        !          1404:    If REG appears more than once, or is used other than as a memory address,
        !          1405:    return (rtx)1.  */
        !          1406: 
        !          1407: static rtx
        !          1408: find_use_as_address (x, reg)
        !          1409:      register rtx x;
        !          1410:      rtx reg;
        !          1411: {
        !          1412:   enum rtx_code code = GET_CODE (x);
        !          1413:   char *fmt = GET_RTX_FORMAT (code);
        !          1414:   register int i;
        !          1415:   register rtx value = 0;
        !          1416:   register rtx tem;
        !          1417: 
        !          1418:   if (code == MEM && XEXP (x, 0) == reg)
        !          1419:     return x;
        !          1420: 
        !          1421:   if (x == reg)
        !          1422:     return (rtx) 1;
        !          1423: 
        !          1424:   for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
        !          1425:     {
        !          1426:       if (fmt[i] == 'e')
        !          1427:        {
        !          1428:          tem = find_use_as_address (XEXP (x, i), reg);
        !          1429:          if (value == 0)
        !          1430:            value = tem;
        !          1431:          else if (tem != 0)
        !          1432:            return (rtx) 1;
        !          1433:        }
        !          1434:       if (fmt[i] == 'E')
        !          1435:        {
        !          1436:          register int j;
        !          1437:          for (j = XVECLEN (x, i) - 1; j >= 0; j--)
        !          1438:            {
        !          1439:              tem = find_use_as_address (XVECEXP (x, i, j), reg);
        !          1440:              if (value == 0)
        !          1441:                value = tem;
        !          1442:              else if (tem != 0)
        !          1443:                return (rtx) 1;
        !          1444:            }
        !          1445:        }
        !          1446:     }
        !          1447: 
        !          1448:   return value;
        !          1449: }
        !          1450: 
        !          1451: #endif /* HAVE_PRE_INCREMENT or HAVE_PRE_DECREMENT */
        !          1452: 
        !          1453: /* Write information about registers and basic blocks into FILE.
        !          1454:    This is part of making a debugging dump.  */
        !          1455: 
        !          1456: dump_flow_info (file)
        !          1457:      FILE *file;
        !          1458: {
        !          1459:   register int i;
        !          1460:   static char *reg_class_names[] = REG_CLASS_NAMES;
        !          1461: 
        !          1462:   fprintf (file, "%d registers.\n", max_regno);
        !          1463: 
        !          1464:   for (i = FIRST_PSEUDO_REGISTER; i < max_regno; i++)
        !          1465:     if (reg_n_refs[i])
        !          1466:       {
        !          1467:        register rtx chain;
        !          1468:        enum reg_class class;
        !          1469:        fprintf (file, "\nRegister %d used %d times across %d insns",
        !          1470:                 i, reg_n_refs[i], reg_live_length[i]);
        !          1471:        if (reg_basic_block[i] >= 0)
        !          1472:          fprintf (file, " in block %d", reg_basic_block[i]);
        !          1473:        if (reg_n_deaths[i] != 1)
        !          1474:          fprintf (file, "; dies in %d places", reg_n_deaths[i]);
        !          1475:        if (reg_crosses_call[i])
        !          1476:          fprintf (file, "; crosses calls");
        !          1477:        if (PSEUDO_REGNO_BYTES (i) != UNITS_PER_WORD)
        !          1478:          fprintf (file, "; %d bytes", PSEUDO_REGNO_BYTES (i));
        !          1479:        class = reg_preferred_class (i);
        !          1480:        if (class != GENERAL_REGS)
        !          1481:          fprintf (file, "; pref %s", reg_class_names[(int) class]);
        !          1482:        if (REGNO_POINTER_FLAG (i))
        !          1483:          fprintf (file, "; pointer");
        !          1484:        fprintf (file, ".\n");
        !          1485:       }
        !          1486:   fprintf (file, "\n%d basic blocks.\n", n_basic_blocks);
        !          1487:   for (i = 0; i < n_basic_blocks; i++)
        !          1488:     {
        !          1489:       register rtx head, jump;
        !          1490:       register int regno;
        !          1491:       fprintf (file, "\nBasic block %d: first insn %d, last %d.\n",
        !          1492:               i,
        !          1493:               INSN_UID (basic_block_head[i]),
        !          1494:               INSN_UID (basic_block_end[i]));
        !          1495:       /* The control flow graph's storage is freed
        !          1496:         now when flow_analysis returns.
        !          1497:         Don't try to print it if it is gone.  */
        !          1498:       if (basic_block_drops_in)
        !          1499:        {
        !          1500:          fprintf (file, "Reached from blocks: ");
        !          1501:          head = basic_block_head[i];
        !          1502:          if (GET_CODE (head) == CODE_LABEL)
        !          1503:            for (jump = LABEL_REFS (head);
        !          1504:                 jump != head;
        !          1505:                 jump = LABEL_NEXTREF (jump))
        !          1506:              {
        !          1507:                register from_block = BLOCK_NUM (CONTAINING_INSN (jump));
        !          1508:                fprintf (file, " %d", from_block);
        !          1509:              }
        !          1510:          if (basic_block_drops_in[i])
        !          1511:            fprintf (file, " previous");
        !          1512:        }
        !          1513:       fprintf (file, "\nRegisters live at start:");
        !          1514:       for (regno = 0; regno < max_regno; regno++)
        !          1515:        {
        !          1516:          register int offset = regno / REGSET_ELT_BITS;
        !          1517:          register int bit = 1 << (regno % REGSET_ELT_BITS);
        !          1518:          if (basic_block_live_at_start[i][offset] & bit)
        !          1519:              fprintf (file, " %d", regno);
        !          1520:        }
        !          1521:       fprintf (file, "\n");
        !          1522:     }
        !          1523:   fprintf (file, "\n");
        !          1524: }

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