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1.1 ! root 1: This is Info file gcc.info, produced by Makeinfo-1.54 from the input ! 2: file gcc.texi. ! 3: ! 4: This file documents the use and the internals of the GNU compiler. ! 5: ! 6: Published by the Free Software Foundation 675 Massachusetts Avenue ! 7: Cambridge, MA 02139 USA ! 8: ! 9: Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc. ! 10: ! 11: Permission is granted to make and distribute verbatim copies of this ! 12: manual provided the copyright notice and this permission notice are ! 13: preserved on all copies. ! 14: ! 15: Permission is granted to copy and distribute modified versions of ! 16: this manual under the conditions for verbatim copying, provided also ! 17: that the sections entitled "GNU General Public License" and "Protect ! 18: Your Freedom--Fight `Look And Feel'" are included exactly as in the ! 19: original, and provided that the entire resulting derived work is ! 20: distributed under the terms of a permission notice identical to this ! 21: one. ! 22: ! 23: Permission is granted to copy and distribute translations of this ! 24: manual into another language, under the above conditions for modified ! 25: versions, except that the sections entitled "GNU General Public ! 26: License" and "Protect Your Freedom--Fight `Look And Feel'", and this ! 27: permission notice, may be included in translations approved by the Free ! 28: Software Foundation instead of in the original English. ! 29: ! 30: ! 31: File: gcc.info, Node: Obsolete Register Macros, Prev: Stack Registers, Up: Registers ! 32: ! 33: Obsolete Macros for Controlling Register Usage ! 34: ---------------------------------------------- ! 35: ! 36: These features do not work very well. They exist because they used ! 37: to be required to generate correct code for the 80387 coprocessor of the ! 38: 80386. They are no longer used by that machine description and may be ! 39: removed in a later version of the compiler. Don't use them! ! 40: ! 41: `OVERLAPPING_REGNO_P (REGNO)' ! 42: If defined, this is a C expression whose value is nonzero if hard ! 43: register number REGNO is an overlapping register. This means a ! 44: hard register which overlaps a hard register with a different ! 45: number. (Such overlap is undesirable, but occasionally it allows ! 46: a machine to be supported which otherwise could not be.) This ! 47: macro must return nonzero for *all* the registers which overlap ! 48: each other. GNU CC can use an overlapping register only in ! 49: certain limited ways. It can be used for allocation within a ! 50: basic block, and may be spilled for reloading; that is all. ! 51: ! 52: If this macro is not defined, it means that none of the hard ! 53: registers overlap each other. This is the usual situation. ! 54: ! 55: `INSN_CLOBBERS_REGNO_P (INSN, REGNO)' ! 56: If defined, this is a C expression whose value should be nonzero if ! 57: the insn INSN has the effect of mysteriously clobbering the ! 58: contents of hard register number REGNO. By "mysterious" we mean ! 59: that the insn's RTL expression doesn't describe such an effect. ! 60: ! 61: If this macro is not defined, it means that no insn clobbers ! 62: registers mysteriously. This is the usual situation; all else ! 63: being equal, it is best for the RTL expression to show all the ! 64: activity. ! 65: ! 66: `PRESERVE_DEATH_INFO_REGNO_P (REGNO)' ! 67: If defined, this is a C expression whose value is nonzero if ! 68: accurate `REG_DEAD' notes are needed for hard register number REGNO ! 69: at the time of outputting the assembler code. When this is so, a ! 70: few optimizations that take place after register allocation and ! 71: could invalidate the death notes are not done when this register is ! 72: involved. ! 73: ! 74: You would arrange to preserve death info for a register when some ! 75: of the code in the machine description which is executed to write ! 76: the assembler code looks at the death notes. This is necessary ! 77: only when the actual hardware feature which GNU CC thinks of as a ! 78: register is not actually a register of the usual sort. (It might, ! 79: for example, be a hardware stack.) ! 80: ! 81: If this macro is not defined, it means that no death notes need to ! 82: be preserved. This is the usual situation. ! 83: ! 84: ! 85: File: gcc.info, Node: Register Classes, Next: Stack and Calling, Prev: Registers, Up: Target Macros ! 86: ! 87: Register Classes ! 88: ================ ! 89: ! 90: On many machines, the numbered registers are not all equivalent. ! 91: For example, certain registers may not be allowed for indexed ! 92: addressing; certain registers may not be allowed in some instructions. ! 93: These machine restrictions are described to the compiler using ! 94: "register classes". ! 95: ! 96: You define a number of register classes, giving each one a name and ! 97: saying which of the registers belong to it. Then you can specify ! 98: register classes that are allowed as operands to particular instruction ! 99: patterns. ! 100: ! 101: In general, each register will belong to several classes. In fact, ! 102: one class must be named `ALL_REGS' and contain all the registers. ! 103: Another class must be named `NO_REGS' and contain no registers. Often ! 104: the union of two classes will be another class; however, this is not ! 105: required. ! 106: ! 107: One of the classes must be named `GENERAL_REGS'. There is nothing ! 108: terribly special about the name, but the operand constraint letters `r' ! 109: and `g' specify this class. If `GENERAL_REGS' is the same as ! 110: `ALL_REGS', just define it as a macro which expands to `ALL_REGS'. ! 111: ! 112: Order the classes so that if class X is contained in class Y then X ! 113: has a lower class number than Y. ! 114: ! 115: The way classes other than `GENERAL_REGS' are specified in operand ! 116: constraints is through machine-dependent operand constraint letters. ! 117: You can define such letters to correspond to various classes, then use ! 118: them in operand constraints. ! 119: ! 120: You should define a class for the union of two classes whenever some ! 121: instruction allows both classes. For example, if an instruction allows ! 122: either a floating point (coprocessor) register or a general register ! 123: for a certain operand, you should define a class `FLOAT_OR_GENERAL_REGS' ! 124: which includes both of them. Otherwise you will get suboptimal code. ! 125: ! 126: You must also specify certain redundant information about the ! 127: register classes: for each class, which classes contain it and which ! 128: ones are contained in it; for each pair of classes, the largest class ! 129: contained in their union. ! 130: ! 131: When a value occupying several consecutive registers is expected in a ! 132: certain class, all the registers used must belong to that class. ! 133: Therefore, register classes cannot be used to enforce a requirement for ! 134: a register pair to start with an even-numbered register. The way to ! 135: specify this requirement is with `HARD_REGNO_MODE_OK'. ! 136: ! 137: Register classes used for input-operands of bitwise-and or shift ! 138: instructions have a special requirement: each such class must have, for ! 139: each fixed-point machine mode, a subclass whose registers can transfer ! 140: that mode to or from memory. For example, on some machines, the ! 141: operations for single-byte values (`QImode') are limited to certain ! 142: registers. When this is so, each register class that is used in a ! 143: bitwise-and or shift instruction must have a subclass consisting of ! 144: registers from which single-byte values can be loaded or stored. This ! 145: is so that `PREFERRED_RELOAD_CLASS' can always have a possible value to ! 146: return. ! 147: ! 148: `enum reg_class' ! 149: An enumeral type that must be defined with all the register class ! 150: names as enumeral values. `NO_REGS' must be first. `ALL_REGS' ! 151: must be the last register class, followed by one more enumeral ! 152: value, `LIM_REG_CLASSES', which is not a register class but rather ! 153: tells how many classes there are. ! 154: ! 155: Each register class has a number, which is the value of casting ! 156: the class name to type `int'. The number serves as an index in ! 157: many of the tables described below. ! 158: ! 159: `N_REG_CLASSES' ! 160: The number of distinct register classes, defined as follows: ! 161: ! 162: #define N_REG_CLASSES (int) LIM_REG_CLASSES ! 163: ! 164: `REG_CLASS_NAMES' ! 165: An initializer containing the names of the register classes as C ! 166: string constants. These names are used in writing some of the ! 167: debugging dumps. ! 168: ! 169: `REG_CLASS_CONTENTS' ! 170: An initializer containing the contents of the register classes, as ! 171: integers which are bit masks. The Nth integer specifies the ! 172: contents of class N. The way the integer MASK is interpreted is ! 173: that register R is in the class if `MASK & (1 << R)' is 1. ! 174: ! 175: When the machine has more than 32 registers, an integer does not ! 176: suffice. Then the integers are replaced by sub-initializers, ! 177: braced groupings containing several integers. Each ! 178: sub-initializer must be suitable as an initializer for the type ! 179: `HARD_REG_SET' which is defined in `hard-reg-set.h'. ! 180: ! 181: `REGNO_REG_CLASS (REGNO)' ! 182: A C expression whose value is a register class containing hard ! 183: register REGNO. In general there is more than one such class; ! 184: choose a class which is "minimal", meaning that no smaller class ! 185: also contains the register. ! 186: ! 187: `BASE_REG_CLASS' ! 188: A macro whose definition is the name of the class to which a valid ! 189: base register must belong. A base register is one used in an ! 190: address which is the register value plus a displacement. ! 191: ! 192: `INDEX_REG_CLASS' ! 193: A macro whose definition is the name of the class to which a valid ! 194: index register must belong. An index register is one used in an ! 195: address where its value is either multiplied by a scale factor or ! 196: added to another register (as well as added to a displacement). ! 197: ! 198: `REG_CLASS_FROM_LETTER (CHAR)' ! 199: A C expression which defines the machine-dependent operand ! 200: constraint letters for register classes. If CHAR is such a ! 201: letter, the value should be the register class corresponding to ! 202: it. Otherwise, the value should be `NO_REGS'. The register ! 203: letter `r', corresponding to class `GENERAL_REGS', will not be ! 204: passed to this macro; you do not need to handle it. ! 205: ! 206: `REGNO_OK_FOR_BASE_P (NUM)' ! 207: A C expression which is nonzero if register number NUM is suitable ! 208: for use as a base register in operand addresses. It may be either ! 209: a suitable hard register or a pseudo register that has been ! 210: allocated such a hard register. ! 211: ! 212: `REGNO_OK_FOR_INDEX_P (NUM)' ! 213: A C expression which is nonzero if register number NUM is suitable ! 214: for use as an index register in operand addresses. It may be ! 215: either a suitable hard register or a pseudo register that has been ! 216: allocated such a hard register. ! 217: ! 218: The difference between an index register and a base register is ! 219: that the index register may be scaled. If an address involves the ! 220: sum of two registers, neither one of them scaled, then either one ! 221: may be labeled the "base" and the other the "index"; but whichever ! 222: labeling is used must fit the machine's constraints of which ! 223: registers may serve in each capacity. The compiler will try both ! 224: labelings, looking for one that is valid, and will reload one or ! 225: both registers only if neither labeling works. ! 226: ! 227: `PREFERRED_RELOAD_CLASS (X, CLASS)' ! 228: A C expression that places additional restrictions on the register ! 229: class to use when it is necessary to copy value X into a register ! 230: in class CLASS. The value is a register class; perhaps CLASS, or ! 231: perhaps another, smaller class. On many machines, the following ! 232: definition is safe: ! 233: ! 234: #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS ! 235: ! 236: Sometimes returning a more restrictive class makes better code. ! 237: For example, on the 68000, when X is an integer constant that is ! 238: in range for a `moveq' instruction, the value of this macro is ! 239: always `DATA_REGS' as long as CLASS includes the data registers. ! 240: Requiring a data register guarantees that a `moveq' will be used. ! 241: ! 242: If X is a `const_double', by returning `NO_REGS' you can force X ! 243: into a memory constant. This is useful on certain machines where ! 244: immediate floating values cannot be loaded into certain kinds of ! 245: registers. ! 246: ! 247: `PREFERRED_OUTPUT_RELOAD_CLASS (X, CLASS)' ! 248: Like `PREFERRED_RELOAD_CLASS', but for output reloads instead of ! 249: input reloads. If you don't define this macro, the default is to ! 250: use CLASS, unchanged. ! 251: ! 252: `LIMIT_RELOAD_CLASS (MODE, CLASS)' ! 253: A C expression that places additional restrictions on the register ! 254: class to use when it is necessary to be able to hold a value of ! 255: mode MODE in a reload register for which class CLASS would ! 256: ordinarily be used. ! 257: ! 258: Unlike `PREFERRED_RELOAD_CLASS', this macro should be used when ! 259: there are certain modes that simply can't go in certain reload ! 260: classes. ! 261: ! 262: The value is a register class; perhaps CLASS, or perhaps another, ! 263: smaller class. ! 264: ! 265: Don't define this macro unless the target machine has limitations ! 266: which require the macro to do something nontrivial. ! 267: ! 268: `SECONDARY_RELOAD_CLASS (CLASS, MODE, X)' ! 269: `SECONDARY_INPUT_RELOAD_CLASS (CLASS, MODE, X)' ! 270: `SECONDARY_OUTPUT_RELOAD_CLASS (CLASS, MODE, X)' ! 271: Many machines have some registers that cannot be copied directly ! 272: to or from memory or even from other types of registers. An ! 273: example is the `MQ' register, which on most machines, can only be ! 274: copied to or from general registers, but not memory. Some ! 275: machines allow copying all registers to and from memory, but ! 276: require a scratch register for stores to some memory locations ! 277: (e.g., those with symbolic address on the RT, and those with ! 278: certain symbolic address on the Sparc when compiling PIC). In ! 279: some cases, both an intermediate and a scratch register are ! 280: required. ! 281: ! 282: You should define these macros to indicate to the reload phase ! 283: that it may need to allocate at least one register for a reload in ! 284: addition to the register to contain the data. Specifically, if ! 285: copying X to a register CLASS in MODE requires an intermediate ! 286: register, you should define `SECONDARY_INPUT_RELOAD_CLASS' to ! 287: return the largest register class all of whose registers can be ! 288: used as intermediate registers or scratch registers. ! 289: ! 290: If copying a register CLASS in MODE to X requires an intermediate ! 291: or scratch register, `SECONDARY_OUTPUT_RELOAD_CLASS' should be ! 292: defined to return the largest register class required. If the ! 293: requirements for input and output reloads are the same, the macro ! 294: `SECONDARY_RELOAD_CLASS' should be used instead of defining both ! 295: macros identically. ! 296: ! 297: The values returned by these macros are often `GENERAL_REGS'. ! 298: Return `NO_REGS' if no spare register is needed; i.e., if X can be ! 299: directly copied to or from a register of CLASS in MODE without ! 300: requiring a scratch register. Do not define this macro if it ! 301: would always return `NO_REGS'. ! 302: ! 303: If a scratch register is required (either with or without an ! 304: intermediate register), you should define patterns for ! 305: `reload_inM' or `reload_outM', as required (*note Standard ! 306: Names::.. These patterns, which will normally be implemented with ! 307: a `define_expand', should be similar to the `movM' patterns, ! 308: except that operand 2 is the scratch register. ! 309: ! 310: Define constraints for the reload register and scratch register ! 311: that contain a single register class. If the original reload ! 312: register (whose class is CLASS) can meet the constraint given in ! 313: the pattern, the value returned by these macros is used for the ! 314: class of the scratch register. Otherwise, two additional reload ! 315: registers are required. Their classes are obtained from the ! 316: constraints in the insn pattern. ! 317: ! 318: X might be a pseudo-register or a `subreg' of a pseudo-register, ! 319: which could either be in a hard register or in memory. Use ! 320: `true_regnum' to find out; it will return -1 if the pseudo is in ! 321: memory and the hard register number if it is in a register. ! 322: ! 323: These macros should not be used in the case where a particular ! 324: class of registers can only be copied to memory and not to another ! 325: class of registers. In that case, secondary reload registers are ! 326: not needed and would not be helpful. Instead, a stack location ! 327: must be used to perform the copy and the `movM' pattern should use ! 328: memory as a intermediate storage. This case often occurs between ! 329: floating-point and general registers. ! 330: ! 331: `SECONDARY_MEMORY_NEEDED (CLASS1, CLASS2, M)' ! 332: Certain machines have the property that some registers cannot be ! 333: copied to some other registers without using memory. Define this ! 334: macro on those machines to be a C expression that is non-zero if ! 335: objects of mode M in registers of CLASS1 can only be copied to ! 336: registers of class CLASS2 by storing a register of CLASS1 into ! 337: memory and loading that memory location into a register of CLASS2. ! 338: ! 339: Do not define this macro if its value would always be zero. ! 340: ! 341: `SECONDARY_MEMORY_NEEDED_RTX (MODE)' ! 342: Normally, when `SECONDARY_MEMORY_NEEDED' is defined, the compiler ! 343: will allocate a stack slot when a memory location for a register ! 344: copy is needed. If this macro is defined, the compiler instead ! 345: uses the memory location defined by this macro. ! 346: ! 347: `SMALL_REGISTER_CLASSES' ! 348: Normally the compiler will avoid choosing spill registers from ! 349: registers that have been explicitly mentioned in the rtl (these ! 350: registers are normally those used to pass parameters and return ! 351: values). However, some machines have so few registers of certain ! 352: classes that there would not be enough registers to use as spill ! 353: registers if this were done. ! 354: ! 355: You should define `SMALL_REGISTER_CLASSES' on those machines. When ! 356: it is defined, the compiler allows registers explicitly used in ! 357: the rtl to be used as spill registers but prevents the compiler ! 358: from extending the lifetime of these registers. ! 359: ! 360: Defining this macro is always safe, but unnecessarily defining ! 361: this macro will reduce the amount of optimizations that can be ! 362: performed in some cases. If this macro is not defined but needs ! 363: to be, the compiler will run out of reload registers and print a ! 364: fatal error message. ! 365: ! 366: For most machines, this macro should not be defined. ! 367: ! 368: `CLASS_LIKELY_SPILLED_P (CLASS)' ! 369: A C expression whose value is nonzero if pseudos that have been ! 370: assigned to registers of class CLASS would likely be spilled ! 371: because registers of CLASS are needed for spill registers. ! 372: ! 373: The default value of this macro returns 1 if CLASS has exactly one ! 374: register and zero otherwise. On most machines, this default ! 375: should be used. Only define this macro to some other expression ! 376: if pseudo allocated by `local-alloc.c' end up in memory because ! 377: their hard registers were needed for spill regisers. If this ! 378: macro returns nonzero for those classes, those pseudos will only ! 379: be allocated by `global.c', which knows how to reallocate the ! 380: pseudo to another register. If there would not be another ! 381: register available for reallocation, you should not change the ! 382: definition of this macro since the only effect of such a ! 383: definition would be to slow down register allocation. ! 384: ! 385: `CLASS_MAX_NREGS (CLASS, MODE)' ! 386: A C expression for the maximum number of consecutive registers of ! 387: class CLASS needed to hold a value of mode MODE. ! 388: ! 389: This is closely related to the macro `HARD_REGNO_NREGS'. In fact, ! 390: the value of the macro `CLASS_MAX_NREGS (CLASS, MODE)' should be ! 391: the maximum value of `HARD_REGNO_NREGS (REGNO, MODE)' for all ! 392: REGNO values in the class CLASS. ! 393: ! 394: This macro helps control the handling of multiple-word values in ! 395: the reload pass. ! 396: ! 397: Three other special macros describe which operands fit which ! 398: constraint letters. ! 399: ! 400: `CONST_OK_FOR_LETTER_P (VALUE, C)' ! 401: A C expression that defines the machine-dependent operand ! 402: constraint letters that specify particular ranges of integer ! 403: values. If C is one of those letters, the expression should check ! 404: that VALUE, an integer, is in the appropriate range and return 1 ! 405: if so, 0 otherwise. If C is not one of those letters, the value ! 406: should be 0 regardless of VALUE. ! 407: ! 408: `CONST_DOUBLE_OK_FOR_LETTER_P (VALUE, C)' ! 409: A C expression that defines the machine-dependent operand ! 410: constraint letters that specify particular ranges of ! 411: `const_double' values. ! 412: ! 413: If C is one of those letters, the expression should check that ! 414: VALUE, an RTX of code `const_double', is in the appropriate range ! 415: and return 1 if so, 0 otherwise. If C is not one of those ! 416: letters, the value should be 0 regardless of VALUE. ! 417: ! 418: `const_double' is used for all floating-point constants and for ! 419: `DImode' fixed-point constants. A given letter can accept either ! 420: or both kinds of values. It can use `GET_MODE' to distinguish ! 421: between these kinds. ! 422: ! 423: `EXTRA_CONSTRAINT (VALUE, C)' ! 424: A C expression that defines the optional machine-dependent ! 425: constraint letters that can be used to segregate specific types of ! 426: operands, usually memory references, for the target machine. ! 427: Normally this macro will not be defined. If it is required for a ! 428: particular target machine, it should return 1 if VALUE corresponds ! 429: to the operand type represented by the constraint letter C. If C ! 430: is not defined as an extra constraint, the value returned should ! 431: be 0 regardless of VALUE. ! 432: ! 433: For example, on the ROMP, load instructions cannot have their ! 434: output in r0 if the memory reference contains a symbolic address. ! 435: Constraint letter `Q' is defined as representing a memory address ! 436: that does *not* contain a symbolic address. An alternative is ! 437: specified with a `Q' constraint on the input and `r' on the ! 438: output. The next alternative specifies `m' on the input and a ! 439: register class that does not include r0 on the output. ! 440: ! 441: ! 442: File: gcc.info, Node: Stack and Calling, Next: Varargs, Prev: Register Classes, Up: Target Macros ! 443: ! 444: Stack Layout and Calling Conventions ! 445: ==================================== ! 446: ! 447: * Menu: ! 448: ! 449: * Frame Layout:: ! 450: * Frame Registers:: ! 451: * Elimination:: ! 452: * Stack Arguments:: ! 453: * Register Arguments:: ! 454: * Scalar Return:: ! 455: * Aggregate Return:: ! 456: * Caller Saves:: ! 457: * Function Entry:: ! 458: * Profiling:: ! 459: ! 460: ! 461: File: gcc.info, Node: Frame Layout, Next: Frame Registers, Up: Stack and Calling ! 462: ! 463: Basic Stack Layout ! 464: ------------------ ! 465: ! 466: `STACK_GROWS_DOWNWARD' ! 467: Define this macro if pushing a word onto the stack moves the stack ! 468: pointer to a smaller address. ! 469: ! 470: When we say, "define this macro if ...," it means that the ! 471: compiler checks this macro only with `#ifdef' so the precise ! 472: definition used does not matter. ! 473: ! 474: `FRAME_GROWS_DOWNWARD' ! 475: Define this macro if the addresses of local variable slots are at ! 476: negative offsets from the frame pointer. ! 477: ! 478: `ARGS_GROW_DOWNWARD' ! 479: Define this macro if successive arguments to a function occupy ! 480: decreasing addresses on the stack. ! 481: ! 482: `STARTING_FRAME_OFFSET' ! 483: Offset from the frame pointer to the first local variable slot to ! 484: be allocated. ! 485: ! 486: If `FRAME_GROWS_DOWNWARD', find the next slot's offset by ! 487: subtracting the first slot's length from `STARTING_FRAME_OFFSET'. ! 488: Otherwise, it is found by adding the length of the first slot to ! 489: the value `STARTING_FRAME_OFFSET'. ! 490: ! 491: `STACK_POINTER_OFFSET' ! 492: Offset from the stack pointer register to the first location at ! 493: which outgoing arguments are placed. If not specified, the ! 494: default value of zero is used. This is the proper value for most ! 495: machines. ! 496: ! 497: If `ARGS_GROW_DOWNWARD', this is the offset to the location above ! 498: the first location at which outgoing arguments are placed. ! 499: ! 500: `FIRST_PARM_OFFSET (FUNDECL)' ! 501: Offset from the argument pointer register to the first argument's ! 502: address. On some machines it may depend on the data type of the ! 503: function. ! 504: ! 505: If `ARGS_GROW_DOWNWARD', this is the offset to the location above ! 506: the first argument's address. ! 507: ! 508: `STACK_DYNAMIC_OFFSET (FUNDECL)' ! 509: Offset from the stack pointer register to an item dynamically ! 510: allocated on the stack, e.g., by `alloca'. ! 511: ! 512: The default value for this macro is `STACK_POINTER_OFFSET' plus the ! 513: length of the outgoing arguments. The default is correct for most ! 514: machines. See `function.c' for details. ! 515: ! 516: `DYNAMIC_CHAIN_ADDRESS (FRAMEADDR)' ! 517: A C expression whose value is RTL representing the address in a ! 518: stack frame where the pointer to the caller's frame is stored. ! 519: Assume that FRAMEADDR is an RTL expression for the address of the ! 520: stack frame itself. ! 521: ! 522: If you don't define this macro, the default is to return the value ! 523: of FRAMEADDR--that is, the stack frame address is also the address ! 524: of the stack word that points to the previous frame. ! 525: ! 526: `SERTUP_FRAME_ADDRESSES ()' ! 527: If defined, a C expression that produces the machine-specific code ! 528: to setup the stack so that arbitrary frames can be accessed. For ! 529: example, on the Sparc, we must flush all of the register windows ! 530: to the stack before we can access arbitrary stack frames. This ! 531: macro will seldom need to be defined. ! 532: ! 533: `RETURN_ADDR_RTX (COUNT, FRAMEADDR)' ! 534: A C expression whose value is RTL representing the value of the ! 535: return address for the frame COUNT steps up from the current frame. ! 536: fRAMEADDR is the frame pointer of the COUNT frame, or the frame ! 537: pointer of the COUNT - 1 frame if `RETURN_ADDR_IN_PREVIOUS_FRAME' ! 538: is defined. ! 539: ! 540: `RETURN_ADDR_IN_PREVIOUS_FRAME' ! 541: Define this if the return address of a particular stack frame is ! 542: accessed from the frame pointer of the previous stack frame. ! 543: ! 544: ! 545: File: gcc.info, Node: Frame Registers, Next: Elimination, Prev: Frame Layout, Up: Stack and Calling ! 546: ! 547: Registers That Address the Stack Frame ! 548: -------------------------------------- ! 549: ! 550: `STACK_POINTER_REGNUM' ! 551: The register number of the stack pointer register, which must also ! 552: be a fixed register according to `FIXED_REGISTERS'. On most ! 553: machines, the hardware determines which register this is. ! 554: ! 555: `FRAME_POINTER_REGNUM' ! 556: The register number of the frame pointer register, which is used to ! 557: access automatic variables in the stack frame. On some machines, ! 558: the hardware determines which register this is. On other ! 559: machines, you can choose any register you wish for this purpose. ! 560: ! 561: `HARD_FRAME_POINTER_REGNUM' ! 562: On some machines the offset between the frame pointer and starting ! 563: offset of the automatic variables is not known until after register ! 564: allocation has been done (for example, because the saved registers ! 565: are between these two locations). On those machines, ! 566: `FRAME_POINTER_REGNUM' as a special, fixed register to be used ! 567: internally until the offset is known, and define ! 568: `HARD_FRAME_POINTER_REGNUM' to be the hard register used for the ! 569: frame pointer. ! 570: ! 571: You should define this macro only in the very rare circumstances ! 572: when it is not possible to calculate the offset between the frame ! 573: pointer and the automatic variables until after register ! 574: allocation has been completed. When this macro is defined, you ! 575: must also indicate in your definition of `ELIMINABLE_REGS' how to ! 576: eliminate `FRAME_POINTER_REGNUM' into either ! 577: `HARD_FRAME_POINTER_REGNUM' or `STACK_POINTER_REGNUM'. ! 578: ! 579: Do not define this macro if it would be the same as ! 580: `FRAME_POINTER_REGNUM'. ! 581: ! 582: `ARG_POINTER_REGNUM' ! 583: The register number of the arg pointer register, which is used to ! 584: access the function's argument list. On some machines, this is ! 585: the same as the frame pointer register. On some machines, the ! 586: hardware determines which register this is. On other machines, ! 587: you can choose any register you wish for this purpose. If this is ! 588: not the same register as the frame pointer register, then you must ! 589: mark it as a fixed register according to `FIXED_REGISTERS', or ! 590: arrange to be able to eliminate it (*note Elimination::.). ! 591: ! 592: `STATIC_CHAIN_REGNUM' ! 593: `STATIC_CHAIN_INCOMING_REGNUM' ! 594: Register numbers used for passing a function's static chain ! 595: pointer. If register windows are used, the register number as ! 596: seen by the called function is `STATIC_CHAIN_INCOMING_REGNUM', ! 597: while the register number as seen by the calling function is ! 598: `STATIC_CHAIN_REGNUM'. If these registers are the same, ! 599: `STATIC_CHAIN_INCOMING_REGNUM' need not be defined. ! 600: ! 601: The static chain register need not be a fixed register. ! 602: ! 603: If the static chain is passed in memory, these macros should not be ! 604: defined; instead, the next two macros should be defined. ! 605: ! 606: `STATIC_CHAIN' ! 607: `STATIC_CHAIN_INCOMING' ! 608: If the static chain is passed in memory, these macros provide rtx ! 609: giving `mem' expressions that denote where they are stored. ! 610: `STATIC_CHAIN' and `STATIC_CHAIN_INCOMING' give the locations as ! 611: seen by the calling and called functions, respectively. Often the ! 612: former will be at an offset from the stack pointer and the latter ! 613: at an offset from the frame pointer. ! 614: ! 615: The variables `stack_pointer_rtx', `frame_pointer_rtx', and ! 616: `arg_pointer_rtx' will have been initialized prior to the use of ! 617: these macros and should be used to refer to those items. ! 618: ! 619: If the static chain is passed in a register, the two previous ! 620: macros should be defined instead. ! 621: ! 622: ! 623: File: gcc.info, Node: Elimination, Next: Stack Arguments, Prev: Frame Registers, Up: Stack and Calling ! 624: ! 625: Eliminating Frame Pointer and Arg Pointer ! 626: ----------------------------------------- ! 627: ! 628: `FRAME_POINTER_REQUIRED' ! 629: A C expression which is nonzero if a function must have and use a ! 630: frame pointer. This expression is evaluated in the reload pass. ! 631: If its value is nonzero the function will have a frame pointer. ! 632: ! 633: The expression can in principle examine the current function and ! 634: decide according to the facts, but on most machines the constant 0 ! 635: or the constant 1 suffices. Use 0 when the machine allows code to ! 636: be generated with no frame pointer, and doing so saves some time ! 637: or space. Use 1 when there is no possible advantage to avoiding a ! 638: frame pointer. ! 639: ! 640: In certain cases, the compiler does not know how to produce valid ! 641: code without a frame pointer. The compiler recognizes those cases ! 642: and automatically gives the function a frame pointer regardless of ! 643: what `FRAME_POINTER_REQUIRED' says. You don't need to worry about ! 644: them. ! 645: ! 646: In a function that does not require a frame pointer, the frame ! 647: pointer register can be allocated for ordinary usage, unless you ! 648: mark it as a fixed register. See `FIXED_REGISTERS' for more ! 649: information. ! 650: ! 651: This macro is ignored and you do not need to define it if the ! 652: function `ELIMINABLE_REGS' is defined. ! 653: ! 654: `INITIAL_FRAME_POINTER_OFFSET (DEPTH-VAR)' ! 655: A C statement to store in the variable DEPTH-VAR the difference ! 656: between the frame pointer and the stack pointer values immediately ! 657: after the function prologue. The value would be computed from ! 658: information such as the result of `get_frame_size ()' and the ! 659: tables of registers `regs_ever_live' and `call_used_regs'. ! 660: ! 661: If `ELIMINABLE_REGS' is defined, this macro will be not be used and ! 662: need not be defined. Otherwise, it must be defined even if ! 663: `FRAME_POINTER_REQUIRED' is defined to always be true; in that ! 664: case, you may set DEPTH-VAR to anything. ! 665: ! 666: `ELIMINABLE_REGS' ! 667: If defined, this macro specifies a table of register pairs used to ! 668: eliminate unneeded registers that point into the stack frame. If ! 669: it is not defined, the only elimination attempted by the compiler ! 670: is to replace references to the frame pointer with references to ! 671: the stack pointer. ! 672: ! 673: The definition of this macro is a list of structure ! 674: initializations, each of which specifies an original and ! 675: replacement register. ! 676: ! 677: On some machines, the position of the argument pointer is not ! 678: known until the compilation is completed. In such a case, a ! 679: separate hard register must be used for the argument pointer. ! 680: This register can be eliminated by replacing it with either the ! 681: frame pointer or the argument pointer, depending on whether or not ! 682: the frame pointer has been eliminated. ! 683: ! 684: In this case, you might specify: ! 685: #define ELIMINABLE_REGS \ ! 686: {{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM}, \ ! 687: {ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM}, \ ! 688: {FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM}} ! 689: ! 690: Note that the elimination of the argument pointer with the stack ! 691: pointer is specified first since that is the preferred elimination. ! 692: ! 693: `CAN_ELIMINATE (FROM-REG, TO-REG)' ! 694: A C expression that returns non-zero if the compiler is allowed to ! 695: try to replace register number FROM-REG with register number ! 696: TO-REG. This macro need only be defined if `ELIMINABLE_REGS' is ! 697: defined, and will usually be the constant 1, since most of the ! 698: cases preventing register elimination are things that the compiler ! 699: already knows about. ! 700: ! 701: `INITIAL_ELIMINATION_OFFSET (FROM-REG, TO-REG, OFFSET-VAR)' ! 702: This macro is similar to `INITIAL_FRAME_POINTER_OFFSET'. It ! 703: specifies the initial difference between the specified pair of ! 704: registers. This macro must be defined if `ELIMINABLE_REGS' is ! 705: defined. ! 706: ! 707: `LONGJMP_RESTORE_FROM_STACK' ! 708: Define this macro if the `longjmp' function restores registers from ! 709: the stack frames, rather than from those saved specifically by ! 710: `setjmp'. Certain quantities must not be kept in registers across ! 711: a call to `setjmp' on such machines. ! 712: ! 713: ! 714: File: gcc.info, Node: Stack Arguments, Next: Register Arguments, Prev: Elimination, Up: Stack and Calling ! 715: ! 716: Passing Function Arguments on the Stack ! 717: --------------------------------------- ! 718: ! 719: The macros in this section control how arguments are passed on the ! 720: stack. See the following section for other macros that control passing ! 721: certain arguments in registers. ! 722: ! 723: `PROMOTE_PROTOTYPES' ! 724: Define this macro if an argument declared in a prototype as an ! 725: integral type smaller than `int' should actually be passed as an ! 726: `int'. In addition to avoiding errors in certain cases of ! 727: mismatch, it also makes for better code on certain machines. ! 728: ! 729: `PUSH_ROUNDING (NPUSHED)' ! 730: A C expression that is the number of bytes actually pushed onto the ! 731: stack when an instruction attempts to push NPUSHED bytes. ! 732: ! 733: If the target machine does not have a push instruction, do not ! 734: define this macro. That directs GNU CC to use an alternate ! 735: strategy: to allocate the entire argument block and then store the ! 736: arguments into it. ! 737: ! 738: On some machines, the definition ! 739: ! 740: #define PUSH_ROUNDING(BYTES) (BYTES) ! 741: ! 742: will suffice. But on other machines, instructions that appear to ! 743: push one byte actually push two bytes in an attempt to maintain ! 744: alignment. Then the definition should be ! 745: ! 746: #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) ! 747: ! 748: `ACCUMULATE_OUTGOING_ARGS' ! 749: If defined, the maximum amount of space required for outgoing ! 750: arguments will be computed and placed into the variable ! 751: `current_function_outgoing_args_size'. No space will be pushed ! 752: onto the stack for each call; instead, the function prologue should ! 753: increase the stack frame size by this amount. ! 754: ! 755: Defining both `PUSH_ROUNDING' and `ACCUMULATE_OUTGOING_ARGS' is ! 756: not proper. ! 757: ! 758: `REG_PARM_STACK_SPACE (FNDECL)' ! 759: Define this macro if functions should assume that stack space has ! 760: been allocated for arguments even when their values are passed in ! 761: registers. ! 762: ! 763: The value of this macro is the size, in bytes, of the area ! 764: reserved for arguments passed in registers for the function ! 765: represented by FNDECL. ! 766: ! 767: This space can be allocated by the caller, or be a part of the ! 768: machine-dependent stack frame: `OUTGOING_REG_PARM_STACK_SPACE' says ! 769: which. ! 770: ! 771: `MAYBE_REG_PARM_STACK_SPACE' ! 772: `FINAL_REG_PARM_STACK_SPACE (CONST_SIZE, VAR_SIZE)' ! 773: Define these macros in addition to the one above if functions might ! 774: allocate stack space for arguments even when their values are ! 775: passed in registers. These should be used when the stack space ! 776: allocated for arguments in registers is not a simple constant ! 777: independent of the function declaration. ! 778: ! 779: The value of the first macro is the size, in bytes, of the area ! 780: that we should initially assume would be reserved for arguments ! 781: passed in registers. ! 782: ! 783: The value of the second macro is the actual size, in bytes, of the ! 784: area that will be reserved for arguments passed in registers. ! 785: This takes two arguments: an integer representing the number of ! 786: bytes of fixed sized arguments on the stack, and a tree ! 787: representing the number of bytes of variable sized arguments on ! 788: the stack. ! 789: ! 790: When these macros are defined, `REG_PARM_STACK_SPACE' will only be ! 791: called for libcall functions, the current function, or for a ! 792: function being called when it is known that such stack space must ! 793: be allocated. In each case this value can be easily computed. ! 794: ! 795: When deciding whether a called function needs such stack space, ! 796: and how much space to reserve, GNU CC uses these two macros ! 797: instead of `REG_PARM_STACK_SPACE'. ! 798: ! 799: `OUTGOING_REG_PARM_STACK_SPACE' ! 800: Define this if it is the responsibility of the caller to allocate ! 801: the area reserved for arguments passed in registers. ! 802: ! 803: If `ACCUMULATE_OUTGOING_ARGS' is defined, this macro controls ! 804: whether the space for these arguments counts in the value of ! 805: `current_function_outgoing_args_size'. ! 806: ! 807: `STACK_PARMS_IN_REG_PARM_AREA' ! 808: Define this macro if `REG_PARM_STACK_SPACE' is defined, but the ! 809: stack parameters don't skip the area specified by it. ! 810: ! 811: Normally, when a parameter is not passed in registers, it is ! 812: placed on the stack beyond the `REG_PARM_STACK_SPACE' area. ! 813: Defining this macro suppresses this behavior and causes the ! 814: parameter to be passed on the stack in its natural location. ! 815: ! 816: `RETURN_POPS_ARGS (FUNTYPE, STACK-SIZE)' ! 817: A C expression that should indicate the number of bytes of its own ! 818: arguments that a function pops on returning, or 0 if the function ! 819: pops no arguments and the caller must therefore pop them all after ! 820: the function returns. ! 821: ! 822: FUNTYPE is a C variable whose value is a tree node that describes ! 823: the function in question. Normally it is a node of type ! 824: `FUNCTION_TYPE' that describes the data type of the function. ! 825: From this it is possible to obtain the data types of the value and ! 826: arguments (if known). ! 827: ! 828: When a call to a library function is being considered, FUNTYPE ! 829: will contain an identifier node for the library function. Thus, if ! 830: you need to distinguish among various library functions, you can ! 831: do so by their names. Note that "library function" in this ! 832: context means a function used to perform arithmetic, whose name is ! 833: known specially in the compiler and was not mentioned in the C ! 834: code being compiled. ! 835: ! 836: STACK-SIZE is the number of bytes of arguments passed on the ! 837: stack. If a variable number of bytes is passed, it is zero, and ! 838: argument popping will always be the responsibility of the calling ! 839: function. ! 840: ! 841: On the Vax, all functions always pop their arguments, so the ! 842: definition of this macro is STACK-SIZE. On the 68000, using the ! 843: standard calling convention, no functions pop their arguments, so ! 844: the value of the macro is always 0 in this case. But an ! 845: alternative calling convention is available in which functions ! 846: that take a fixed number of arguments pop them but other functions ! 847: (such as `printf') pop nothing (the caller pops all). When this ! 848: convention is in use, FUNTYPE is examined to determine whether a ! 849: function takes a fixed number of arguments. ! 850: ! 851: ! 852: File: gcc.info, Node: Register Arguments, Next: Scalar Return, Prev: Stack Arguments, Up: Stack and Calling ! 853: ! 854: Passing Arguments in Registers ! 855: ------------------------------ ! 856: ! 857: This section describes the macros which let you control how various ! 858: types of arguments are passed in registers or how they are arranged in ! 859: the stack. ! 860: ! 861: `FUNCTION_ARG (CUM, MODE, TYPE, NAMED)' ! 862: A C expression that controls whether a function argument is passed ! 863: in a register, and which register. ! 864: ! 865: The arguments are CUM, which summarizes all the previous ! 866: arguments; MODE, the machine mode of the argument; TYPE, the data ! 867: type of the argument as a tree node or 0 if that is not known ! 868: (which happens for C support library functions); and NAMED, which ! 869: is 1 for an ordinary argument and 0 for nameless arguments that ! 870: correspond to `...' in the called function's prototype. ! 871: ! 872: The value of the expression should either be a `reg' RTX for the ! 873: hard register in which to pass the argument, or zero to pass the ! 874: argument on the stack. ! 875: ! 876: For machines like the Vax and 68000, where normally all arguments ! 877: are pushed, zero suffices as a definition. ! 878: ! 879: The usual way to make the ANSI library `stdarg.h' work on a machine ! 880: where some arguments are usually passed in registers, is to cause ! 881: nameless arguments to be passed on the stack instead. This is done ! 882: by making `FUNCTION_ARG' return 0 whenever NAMED is 0. ! 883: ! 884: You may use the macro `MUST_PASS_IN_STACK (MODE, TYPE)' in the ! 885: definition of this macro to determine if this argument is of a ! 886: type that must be passed in the stack. If `REG_PARM_STACK_SPACE' ! 887: is not defined and `FUNCTION_ARG' returns non-zero for such an ! 888: argument, the compiler will abort. If `REG_PARM_STACK_SPACE' is ! 889: defined, the argument will be computed in the stack and then ! 890: loaded into a register. ! 891: ! 892: `FUNCTION_INCOMING_ARG (CUM, MODE, TYPE, NAMED)' ! 893: Define this macro if the target machine has "register windows", so ! 894: that the register in which a function sees an arguments is not ! 895: necessarily the same as the one in which the caller passed the ! 896: argument. ! 897: ! 898: For such machines, `FUNCTION_ARG' computes the register in which ! 899: the caller passes the value, and `FUNCTION_INCOMING_ARG' should be ! 900: defined in a similar fashion to tell the function being called ! 901: where the arguments will arrive. ! 902: ! 903: If `FUNCTION_INCOMING_ARG' is not defined, `FUNCTION_ARG' serves ! 904: both purposes. ! 905: ! 906: `FUNCTION_ARG_PARTIAL_NREGS (CUM, MODE, TYPE, NAMED)' ! 907: A C expression for the number of words, at the beginning of an ! 908: argument, must be put in registers. The value must be zero for ! 909: arguments that are passed entirely in registers or that are ! 910: entirely pushed on the stack. ! 911: ! 912: On some machines, certain arguments must be passed partially in ! 913: registers and partially in memory. On these machines, typically ! 914: the first N words of arguments are passed in registers, and the ! 915: rest on the stack. If a multi-word argument (a `double' or a ! 916: structure) crosses that boundary, its first few words must be ! 917: passed in registers and the rest must be pushed. This macro tells ! 918: the compiler when this occurs, and how many of the words should go ! 919: in registers. ! 920: ! 921: `FUNCTION_ARG' for these arguments should return the first ! 922: register to be used by the caller for this argument; likewise ! 923: `FUNCTION_INCOMING_ARG', for the called function. ! 924: ! 925: `FUNCTION_ARG_PASS_BY_REFERENCE (CUM, MODE, TYPE, NAMED)' ! 926: A C expression that indicates when an argument must be passed by ! 927: reference. If nonzero for an argument, a copy of that argument is ! 928: made in memory and a pointer to the argument is passed instead of ! 929: the argument itself. The pointer is passed in whatever way is ! 930: appropriate for passing a pointer to that type. ! 931: ! 932: On machines where `REG_PARM_STACK_SPACE' is not defined, a suitable ! 933: definition of this macro might be ! 934: #define FUNCTION_ARG_PASS_BY_REFERENCE\ ! 935: (CUM, MODE, TYPE, NAMED) \ ! 936: MUST_PASS_IN_STACK (MODE, TYPE) ! 937: ! 938: `FUNCTION_ARG_CALLEE_COPIES (CUM, MODE, TYPE, NAMED)' ! 939: If defined, a C expression that indicates when it is the called ! 940: function's responsibility to make a copy of arguments passed by ! 941: invisible reference. Normally, the caller makes a copy and passes ! 942: the address of the copy to the routine being called. When ! 943: FUNCTION_ARG_CALLEE_COPIES is defined and is nonzero, the caller ! 944: does not make a copy. Instead, it passes a pointer to the "live" ! 945: value. The called function must not modify this value. If it can ! 946: be determined that the value won't be modified, it need not make a ! 947: copy; otherwise a copy must be made. ! 948: ! 949: `CUMULATIVE_ARGS' ! 950: A C type for declaring a variable that is used as the first ! 951: argument of `FUNCTION_ARG' and other related values. For some ! 952: target machines, the type `int' suffices and can hold the number ! 953: of bytes of argument so far. ! 954: ! 955: There is no need to record in `CUMULATIVE_ARGS' anything about the ! 956: arguments that have been passed on the stack. The compiler has ! 957: other variables to keep track of that. For target machines on ! 958: which all arguments are passed on the stack, there is no need to ! 959: store anything in `CUMULATIVE_ARGS'; however, the data structure ! 960: must exist and should not be empty, so use `int'. ! 961: ! 962: `INIT_CUMULATIVE_ARGS (CUM, FNTYPE, LIBNAME)' ! 963: A C statement (sans semicolon) for initializing the variable CUM ! 964: for the state at the beginning of the argument list. The variable ! 965: has type `CUMULATIVE_ARGS'. The value of FNTYPE is the tree node ! 966: for the data type of the function which will receive the args, or 0 ! 967: if the args are to a compiler support library function. ! 968: ! 969: When processing a call to a compiler support library function, ! 970: LIBNAME identifies which one. It is a `symbol_ref' rtx which ! 971: contains the name of the function, as a string. LIBNAME is 0 when ! 972: an ordinary C function call is being processed. Thus, each time ! 973: this macro is called, either LIBNAME or FNTYPE is nonzero, but ! 974: never both of them at once. ! 975: ! 976: `INIT_CUMULATIVE_INCOMING_ARGS (CUM, FNTYPE, LIBNAME)' ! 977: Like `INIT_CUMULATIVE_ARGS' but overrides it for the purposes of ! 978: finding the arguments for the function being compiled. If this ! 979: macro is undefined, `INIT_CUMULATIVE_ARGS' is used instead. ! 980: ! 981: The value passed for LIBNAME is always 0, since library routines ! 982: with special calling conventions are never compiled with GNU CC. ! 983: The argument LIBNAME exists for symmetry with ! 984: `INIT_CUMULATIVE_ARGS'. ! 985: ! 986: `FUNCTION_ARG_ADVANCE (CUM, MODE, TYPE, NAMED)' ! 987: A C statement (sans semicolon) to update the summarizer variable ! 988: CUM to advance past an argument in the argument list. The values ! 989: MODE, TYPE and NAMED describe that argument. Once this is done, ! 990: the variable CUM is suitable for analyzing the *following* ! 991: argument with `FUNCTION_ARG', etc. ! 992: ! 993: This macro need not do anything if the argument in question was ! 994: passed on the stack. The compiler knows how to track the amount ! 995: of stack space used for arguments without any special help. ! 996: ! 997: `FUNCTION_ARG_PADDING (MODE, TYPE)' ! 998: If defined, a C expression which determines whether, and in which ! 999: direction, to pad out an argument with extra space. The value ! 1000: should be of type `enum direction': either `upward' to pad above ! 1001: the argument, `downward' to pad below, or `none' to inhibit ! 1002: padding. ! 1003: ! 1004: The *amount* of padding is always just enough to reach the next ! 1005: multiple of `FUNCTION_ARG_BOUNDARY'; this macro does not control ! 1006: it. ! 1007: ! 1008: This macro has a default definition which is right for most ! 1009: systems. For little-endian machines, the default is to pad ! 1010: upward. For big-endian machines, the default is to pad downward ! 1011: for an argument of constant size shorter than an `int', and upward ! 1012: otherwise. ! 1013: ! 1014: `FUNCTION_ARG_BOUNDARY (MODE, TYPE)' ! 1015: If defined, a C expression that gives the alignment boundary, in ! 1016: bits, of an argument with the specified mode and type. If it is ! 1017: not defined, `PARM_BOUNDARY' is used for all arguments. ! 1018: ! 1019: `FUNCTION_ARG_REGNO_P (REGNO)' ! 1020: A C expression that is nonzero if REGNO is the number of a hard ! 1021: register in which function arguments are sometimes passed. This ! 1022: does *not* include implicit arguments such as the static chain and ! 1023: the structure-value address. On many machines, no registers can be ! 1024: used for this purpose since all function arguments are pushed on ! 1025: the stack. ! 1026:
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