/* Alias analysis for GNU C Copyright (C) 1997 Free Software Foundation, Inc. Contributed by John Carr (jfc@mit.edu). This file is part of GNU CC. GNU CC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU CC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU CC; see the file COPYING. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include "config.h" #include "rtl.h" #include "expr.h" #include "regs.h" #include "hard-reg-set.h" #include "flags.h" static rtx canon_rtx PROTO((rtx)); static int rtx_equal_for_memref_p PROTO((rtx, rtx)); static rtx find_symbolic_term PROTO((rtx)); static int memrefs_conflict_p PROTO((int, rtx, int, rtx, HOST_WIDE_INT)); /* Set up all info needed to perform alias analysis on memory references. */ #define SIZE_FOR_MODE(X) (GET_MODE_SIZE (GET_MODE (X))) /* Cap the number of passes we make over the insns propagating alias information through set chains. 10 is a completely arbitrary choice. */ #define MAX_ALIAS_LOOP_PASSES 10 /* reg_base_value[N] gives an address to which register N is related. If all sets after the first add or subtract to the current value or otherwise modify it so it does not point to a different top level object, reg_base_value[N] is equal to the address part of the source of the first set. A base address can be an ADDRESS, SYMBOL_REF, or LABEL_REF. ADDRESS expressions represent certain special values: function arguments and the stack, frame, and argument pointers. The contents of an address expression are not used (but they are descriptive for debugging); only the address and mode matter. Pointer equality, not rtx_equal_p, determines whether two ADDRESS expressions refer to the same base address. The mode determines whether it is a function argument or other special value. */ rtx *reg_base_value; rtx *new_reg_base_value; unsigned int reg_base_value_size; /* size of reg_base_value array */ #define REG_BASE_VALUE(X) \ (REGNO (X) < reg_base_value_size ? reg_base_value[REGNO (X)] : 0) /* Vector indexed by N giving the initial (unchanging) value known for pseudo-register N. */ rtx *reg_known_value; /* Indicates number of valid entries in reg_known_value. */ static int reg_known_value_size; /* Vector recording for each reg_known_value whether it is due to a REG_EQUIV note. Future passes (viz., reload) may replace the pseudo with the equivalent expression and so we account for the dependences that would be introduced if that happens. */ /* ??? This is a problem only on the Convex. The REG_EQUIV notes created in assign_parms mention the arg pointer, and there are explicit insns in the RTL that modify the arg pointer. Thus we must ensure that such insns don't get scheduled across each other because that would invalidate the REG_EQUIV notes. One could argue that the REG_EQUIV notes are wrong, but solving the problem in the scheduler will likely give better code, so we do it here. */ char *reg_known_equiv_p; /* True when scanning insns from the start of the rtl to the NOTE_INSN_FUNCTION_BEG note. */ static int copying_arguments; /* Inside SRC, the source of a SET, find a base address. */ static rtx find_base_value (src) register rtx src; { switch (GET_CODE (src)) { case SYMBOL_REF: case LABEL_REF: return src; case REG: /* At the start of a function argument registers have known base values which may be lost later. Returning an ADDRESS expression here allows optimization based on argument values even when the argument registers are used for other purposes. */ if (REGNO (src) < FIRST_PSEUDO_REGISTER && copying_arguments) return new_reg_base_value[REGNO (src)]; /* If a pseudo has a known base value, return it. Do not do this for hard regs since it can result in a circular dependency chain for registers which have values at function entry. The test above is not sufficient because the scheduler may move a copy out of an arg reg past the NOTE_INSN_FUNCTION_BEGIN. */ if (REGNO (src) >= FIRST_PSEUDO_REGISTER && reg_base_value[REGNO (src)]) return reg_base_value[REGNO (src)]; return src; case MEM: /* Check for an argument passed in memory. Only record in the copying-arguments block; it is too hard to track changes otherwise. */ if (copying_arguments && (XEXP (src, 0) == arg_pointer_rtx || (GET_CODE (XEXP (src, 0)) == PLUS && XEXP (XEXP (src, 0), 0) == arg_pointer_rtx))) return gen_rtx (ADDRESS, VOIDmode, src); return 0; case CONST: src = XEXP (src, 0); if (GET_CODE (src) != PLUS && GET_CODE (src) != MINUS) break; /* fall through */ case PLUS: case MINUS: { rtx temp, src_0 = XEXP (src, 0), src_1 = XEXP (src, 1); /* If either operand is a REG, then see if we already have a known value for it. */ if (GET_CODE (src_0) == REG) { temp = find_base_value (src_0); if (temp) src_0 = temp; } if (GET_CODE (src_1) == REG) { temp = find_base_value (src_1); if (temp) src_1 = temp; } /* Guess which operand is the base address. If either operand is a symbol, then it is the base. If either operand is a CONST_INT, then the other is the base. */ if (GET_CODE (src_1) == CONST_INT || GET_CODE (src_0) == SYMBOL_REF || GET_CODE (src_0) == LABEL_REF || GET_CODE (src_0) == CONST) return find_base_value (src_0); if (GET_CODE (src_0) == CONST_INT || GET_CODE (src_1) == SYMBOL_REF || GET_CODE (src_1) == LABEL_REF || GET_CODE (src_1) == CONST) return find_base_value (src_1); /* This might not be necessary anymore. If either operand is a REG that is a known pointer, then it is the base. */ if (GET_CODE (src_0) == REG && REGNO_POINTER_FLAG (REGNO (src_0))) return find_base_value (src_0); if (GET_CODE (src_1) == REG && REGNO_POINTER_FLAG (REGNO (src_1))) return find_base_value (src_1); return 0; } case LO_SUM: /* The standard form is (lo_sum reg sym) so look only at the second operand. */ return find_base_value (XEXP (src, 1)); case AND: /* If the second operand is constant set the base address to the first operand. */ if (GET_CODE (XEXP (src, 1)) == CONST_INT && INTVAL (XEXP (src, 1)) != 0) return find_base_value (XEXP (src, 0)); return 0; case HIGH: return find_base_value (XEXP (src, 0)); } return 0; } /* Called from init_alias_analysis indirectly through note_stores. */ /* while scanning insns to find base values, reg_seen[N] is nonzero if register N has been set in this function. */ static char *reg_seen; /* */ static int unique_id; static void record_set (dest, set) rtx dest, set; { register int regno; rtx src; if (GET_CODE (dest) != REG) return; regno = REGNO (dest); if (set) { /* A CLOBBER wipes out any old value but does not prevent a previously unset register from acquiring a base address (i.e. reg_seen is not set). */ if (GET_CODE (set) == CLOBBER) { new_reg_base_value[regno] = 0; return; } src = SET_SRC (set); } else { if (reg_seen[regno]) { new_reg_base_value[regno] = 0; return; } reg_seen[regno] = 1; new_reg_base_value[regno] = gen_rtx (ADDRESS, Pmode, GEN_INT (unique_id++)); return; } /* This is not the first set. If the new value is not related to the old value, forget the base value. Note that the following code is not detected: extern int x, y; int *p = &x; p += (&y-&x); ANSI C does not allow computing the difference of addresses of distinct top level objects. */ if (new_reg_base_value[regno]) switch (GET_CODE (src)) { case LO_SUM: case PLUS: case MINUS: if (XEXP (src, 0) != dest && XEXP (src, 1) != dest) new_reg_base_value[regno] = 0; break; case AND: if (XEXP (src, 0) != dest || GET_CODE (XEXP (src, 1)) != CONST_INT) new_reg_base_value[regno] = 0; break; default: new_reg_base_value[regno] = 0; break; } /* If this is the first set of a register, record the value. */ else if ((regno >= FIRST_PSEUDO_REGISTER || ! fixed_regs[regno]) && ! reg_seen[regno] && new_reg_base_value[regno] == 0) new_reg_base_value[regno] = find_base_value (src); reg_seen[regno] = 1; } /* Called from loop optimization when a new pseudo-register is created. */ void record_base_value (regno, val) int regno; rtx val; { if (!flag_alias_check || regno >= reg_base_value_size) return; if (GET_CODE (val) == REG) { if (REGNO (val) < reg_base_value_size) reg_base_value[regno] = reg_base_value[REGNO (val)]; return; } reg_base_value[regno] = find_base_value (val); } static rtx canon_rtx (x) rtx x; { /* Recursively look for equivalences. */ if (GET_CODE (x) == REG && REGNO (x) >= FIRST_PSEUDO_REGISTER && REGNO (x) < reg_known_value_size) return reg_known_value[REGNO (x)] == x ? x : canon_rtx (reg_known_value[REGNO (x)]); else if (GET_CODE (x) == PLUS) { rtx x0 = canon_rtx (XEXP (x, 0)); rtx x1 = canon_rtx (XEXP (x, 1)); if (x0 != XEXP (x, 0) || x1 != XEXP (x, 1)) { /* We can tolerate LO_SUMs being offset here; these rtl are used for nothing other than comparisons. */ if (GET_CODE (x0) == CONST_INT) return plus_constant_for_output (x1, INTVAL (x0)); else if (GET_CODE (x1) == CONST_INT) return plus_constant_for_output (x0, INTVAL (x1)); return gen_rtx (PLUS, GET_MODE (x), x0, x1); } } /* This gives us much better alias analysis when called from the loop optimizer. Note we want to leave the original MEM alone, but need to return the canonicalized MEM with all the flags with their original values. */ else if (GET_CODE (x) == MEM) { rtx addr = canon_rtx (XEXP (x, 0)); if (addr != XEXP (x, 0)) { rtx new = gen_rtx (MEM, GET_MODE (x), addr); MEM_VOLATILE_P (new) = MEM_VOLATILE_P (x); RTX_UNCHANGING_P (new) = RTX_UNCHANGING_P (x); MEM_IN_STRUCT_P (new) = MEM_IN_STRUCT_P (x); x = new; } } return x; } /* Return 1 if X and Y are identical-looking rtx's. We use the data in reg_known_value above to see if two registers with different numbers are, in fact, equivalent. */ static int rtx_equal_for_memref_p (x, y) rtx x, y; { register int i; register int j; register enum rtx_code code; register char *fmt; if (x == 0 && y == 0) return 1; if (x == 0 || y == 0) return 0; x = canon_rtx (x); y = canon_rtx (y); if (x == y) return 1; code = GET_CODE (x); /* Rtx's of different codes cannot be equal. */ if (code != GET_CODE (y)) return 0; /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. (REG:SI x) and (REG:HI x) are NOT equivalent. */ if (GET_MODE (x) != GET_MODE (y)) return 0; /* REG, LABEL_REF, and SYMBOL_REF can be compared nonrecursively. */ if (code == REG) return REGNO (x) == REGNO (y); if (code == LABEL_REF) return XEXP (x, 0) == XEXP (y, 0); if (code == SYMBOL_REF) return XSTR (x, 0) == XSTR (y, 0); /* For commutative operations, the RTX match if the operand match in any order. Also handle the simple binary and unary cases without a loop. */ if (code == EQ || code == NE || GET_RTX_CLASS (code) == 'c') return ((rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0)) && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1))) || (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 1)) && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 0)))); else if (GET_RTX_CLASS (code) == '<' || GET_RTX_CLASS (code) == '2') return (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0)) && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1))); else if (GET_RTX_CLASS (code) == '1') return rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0)); /* Compare the elements. If any pair of corresponding elements fail to match, return 0 for the whole things. */ fmt = GET_RTX_FORMAT (code); for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--) { switch (fmt[i]) { case 'w': if (XWINT (x, i) != XWINT (y, i)) return 0; break; case 'n': case 'i': if (XINT (x, i) != XINT (y, i)) return 0; break; case 'V': case 'E': /* Two vectors must have the same length. */ if (XVECLEN (x, i) != XVECLEN (y, i)) return 0; /* And the corresponding elements must match. */ for (j = 0; j < XVECLEN (x, i); j++) if (rtx_equal_for_memref_p (XVECEXP (x, i, j), XVECEXP (y, i, j)) == 0) return 0; break; case 'e': if (rtx_equal_for_memref_p (XEXP (x, i), XEXP (y, i)) == 0) return 0; break; case 'S': case 's': if (strcmp (XSTR (x, i), XSTR (y, i))) return 0; break; case 'u': /* These are just backpointers, so they don't matter. */ break; case '0': break; /* It is believed that rtx's at this level will never contain anything but integers and other rtx's, except for within LABEL_REFs and SYMBOL_REFs. */ default: abort (); } } return 1; } /* Given an rtx X, find a SYMBOL_REF or LABEL_REF within X and return it, or return 0 if none found. */ static rtx find_symbolic_term (x) rtx x; { register int i; register enum rtx_code code; register char *fmt; code = GET_CODE (x); if (code == SYMBOL_REF || code == LABEL_REF) return x; if (GET_RTX_CLASS (code) == 'o') return 0; fmt = GET_RTX_FORMAT (code); for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--) { rtx t; if (fmt[i] == 'e') { t = find_symbolic_term (XEXP (x, i)); if (t != 0) return t; } else if (fmt[i] == 'E') break; } return 0; } static rtx find_base_term (x) register rtx x; { switch (GET_CODE (x)) { case REG: return REG_BASE_VALUE (x); case HIGH: return find_base_term (XEXP (x, 0)); case PRE_INC: case PRE_DEC: case POST_INC: case POST_DEC: return find_base_term (XEXP (x, 0)); case CONST: x = XEXP (x, 0); if (GET_CODE (x) != PLUS && GET_CODE (x) != MINUS) return 0; /* fall through */ case LO_SUM: case PLUS: case MINUS: { rtx tmp = find_base_term (XEXP (x, 0)); if (tmp) return tmp; return find_base_term (XEXP (x, 1)); } case AND: if (GET_CODE (XEXP (x, 0)) == REG && GET_CODE (XEXP (x, 1)) == CONST_INT) return REG_BASE_VALUE (XEXP (x, 0)); return 0; case SYMBOL_REF: case LABEL_REF: return x; default: return 0; } } /* Return 0 if the addresses X and Y are known to point to different objects, 1 if they might be pointers to the same object. */ static int base_alias_check (x, y) rtx x, y; { rtx x_base = find_base_term (x); rtx y_base = find_base_term (y); /* If either base address is unknown or the base addresses are equal, nothing is known about aliasing. */ if (x_base == 0 || y_base == 0 || rtx_equal_p (x_base, y_base)) return 1; /* The base addresses of the read and write are different expressions. If they are both symbols and they are not accessed via AND, there is no conflict. */ /* XXX: We can bring knowledge of object alignment and offset into play here. For example, on alpha, "char a, b;" can alias one another, though "char a; long b;" cannot. Similarly, offsets into strutures may be brought into play. Given "char a, b[40];", a and b[1] may overlap, but a and b[20] do not. */ if (GET_CODE (x_base) != ADDRESS && GET_CODE (y_base) != ADDRESS) { return GET_CODE (x) == AND || GET_CODE (y) == AND; } /* If one address is a stack reference there can be no alias: stack references using different base registers do not alias, a stack reference can not alias a parameter, and a stack reference can not alias a global. */ if ((GET_CODE (x_base) == ADDRESS && GET_MODE (x_base) == Pmode) || (GET_CODE (y_base) == ADDRESS && GET_MODE (y_base) == Pmode)) return 0; if (! flag_argument_noalias) return 1; if (flag_argument_noalias > 1) return 0; /* Weak noalias assertion (arguments are distinct, but may match globals). */ return ! (GET_MODE (x_base) == VOIDmode && GET_MODE (y_base) == VOIDmode); } /* Return nonzero if X and Y (memory addresses) could reference the same location in memory. C is an offset accumulator. When C is nonzero, we are testing aliases between X and Y + C. XSIZE is the size in bytes of the X reference, similarly YSIZE is the size in bytes for Y. If XSIZE or YSIZE is zero, we do not know the amount of memory being referenced (the reference was BLKmode), so make the most pessimistic assumptions. If XSIZE or YSIZE is negative, we may access memory outside the object being referenced as a side effect. This can happen when using AND to align memory references, as is done on the Alpha. We recognize the following cases of non-conflicting memory: (1) addresses involving the frame pointer cannot conflict with addresses involving static variables. (2) static variables with different addresses cannot conflict. Nice to notice that varying addresses cannot conflict with fp if no local variables had their addresses taken, but that's too hard now. */ static int memrefs_conflict_p (xsize, x, ysize, y, c) register rtx x, y; int xsize, ysize; HOST_WIDE_INT c; { if (GET_CODE (x) == HIGH) x = XEXP (x, 0); else if (GET_CODE (x) == LO_SUM) x = XEXP (x, 1); else x = canon_rtx (x); if (GET_CODE (y) == HIGH) y = XEXP (y, 0); else if (GET_CODE (y) == LO_SUM) y = XEXP (y, 1); else y = canon_rtx (y); if (rtx_equal_for_memref_p (x, y)) { if (xsize <= 0 || ysize <= 0) return 1; if (c >= 0 && xsize > c) return 1; if (c < 0 && ysize+c > 0) return 1; return 0; } if (y == frame_pointer_rtx || y == hard_frame_pointer_rtx || y == stack_pointer_rtx || y == arg_pointer_rtx) { rtx t = y; int tsize = ysize; y = x; ysize = xsize; x = t; xsize = tsize; } if (x == frame_pointer_rtx || x == hard_frame_pointer_rtx || x == stack_pointer_rtx || x == arg_pointer_rtx) { rtx y1; if (CONSTANT_P (y)) return 0; if (GET_CODE (y) == PLUS && canon_rtx (XEXP (y, 0)) == x && (y1 = canon_rtx (XEXP (y, 1))) && GET_CODE (y1) == CONST_INT) { c += INTVAL (y1); return (xsize <= 0 || ysize <= 0 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); } if (GET_CODE (y) == PLUS && (y1 = canon_rtx (XEXP (y, 0))) && CONSTANT_P (y1)) return 0; return 1; } if (GET_CODE (x) == PLUS) { /* The fact that X is canonicalized means that this PLUS rtx is canonicalized. */ rtx x0 = XEXP (x, 0); rtx x1 = XEXP (x, 1); if (GET_CODE (y) == PLUS) { /* The fact that Y is canonicalized means that this PLUS rtx is canonicalized. */ rtx y0 = XEXP (y, 0); rtx y1 = XEXP (y, 1); if (rtx_equal_for_memref_p (x1, y1)) return memrefs_conflict_p (xsize, x0, ysize, y0, c); if (rtx_equal_for_memref_p (x0, y0)) return memrefs_conflict_p (xsize, x1, ysize, y1, c); if (GET_CODE (x1) == CONST_INT) if (GET_CODE (y1) == CONST_INT) return memrefs_conflict_p (xsize, x0, ysize, y0, c - INTVAL (x1) + INTVAL (y1)); else return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1)); else if (GET_CODE (y1) == CONST_INT) return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1)); /* Handle case where we cannot understand iteration operators, but we notice that the base addresses are distinct objects. */ /* ??? Is this still necessary? */ x = find_symbolic_term (x); if (x == 0) return 1; y = find_symbolic_term (y); if (y == 0) return 1; return rtx_equal_for_memref_p (x, y); } else if (GET_CODE (x1) == CONST_INT) return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1)); } else if (GET_CODE (y) == PLUS) { /* The fact that Y is canonicalized means that this PLUS rtx is canonicalized. */ rtx y0 = XEXP (y, 0); rtx y1 = XEXP (y, 1); if (GET_CODE (y1) == CONST_INT) return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1)); else return 1; } if (GET_CODE (x) == GET_CODE (y)) switch (GET_CODE (x)) { case MULT: { /* Handle cases where we expect the second operands to be the same, and check only whether the first operand would conflict or not. */ rtx x0, y0; rtx x1 = canon_rtx (XEXP (x, 1)); rtx y1 = canon_rtx (XEXP (y, 1)); if (! rtx_equal_for_memref_p (x1, y1)) return 1; x0 = canon_rtx (XEXP (x, 0)); y0 = canon_rtx (XEXP (y, 0)); if (rtx_equal_for_memref_p (x0, y0)) return (xsize == 0 || ysize == 0 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); /* Can't properly adjust our sizes. */ if (GET_CODE (x1) != CONST_INT) return 1; xsize /= INTVAL (x1); ysize /= INTVAL (x1); c /= INTVAL (x1); return memrefs_conflict_p (xsize, x0, ysize, y0, c); } } /* Treat an access through an AND (e.g. a subword access on an Alpha) as an access with indeterminate size. */ if (GET_CODE (x) == AND && GET_CODE (XEXP (x, 1)) == CONST_INT) return memrefs_conflict_p (-1, XEXP (x, 0), ysize, y, c); if (GET_CODE (y) == AND && GET_CODE (XEXP (y, 1)) == CONST_INT) { /* XXX: If we are indexing far enough into the array/structure, we may yet be able to determine that we can not overlap. But we also need to that we are far enough from the end not to overlap a following reference, so we do nothing for now. */ return memrefs_conflict_p (xsize, x, -1, XEXP (y, 0), c); } if (CONSTANT_P (x)) { if (GET_CODE (x) == CONST_INT && GET_CODE (y) == CONST_INT) { c += (INTVAL (y) - INTVAL (x)); return (xsize <= 0 || ysize <= 0 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)); } if (GET_CODE (x) == CONST) { if (GET_CODE (y) == CONST) return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)), ysize, canon_rtx (XEXP (y, 0)), c); else return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)), ysize, y, c); } if (GET_CODE (y) == CONST) return memrefs_conflict_p (xsize, x, ysize, canon_rtx (XEXP (y, 0)), c); if (CONSTANT_P (y)) return (xsize < 0 || ysize < 0 || (rtx_equal_for_memref_p (x, y) && (xsize == 0 || ysize == 0 || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)))); return 1; } return 1; } /* Functions to compute memory dependencies. Since we process the insns in execution order, we can build tables to keep track of what registers are fixed (and not aliased), what registers are varying in known ways, and what registers are varying in unknown ways. If both memory references are volatile, then there must always be a dependence between the two references, since their order can not be changed. A volatile and non-volatile reference can be interchanged though. A MEM_IN_STRUCT reference at a non-QImode non-AND varying address can never conflict with a non-MEM_IN_STRUCT reference at a fixed address. We must allow QImode aliasing because the ANSI C standard allows character pointers to alias anything. We are assuming that characters are always QImode here. We also must allow AND addresses, because they may generate accesses outside the object being referenced. This is used to generate aligned addresses from unaligned addresses, for instance, the alpha storeqi_unaligned pattern. */ /* Read dependence: X is read after read in MEM takes place. There can only be a dependence here if both reads are volatile. */ int read_dependence (mem, x) rtx mem; rtx x; { return MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem); } /* True dependence: X is read after store in MEM takes place. */ int true_dependence (mem, mem_mode, x, varies) rtx mem; enum machine_mode mem_mode; rtx x; int (*varies)(); { rtx x_addr, mem_addr; if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem)) return 1; x_addr = XEXP (x, 0); mem_addr = XEXP (mem, 0); if (flag_alias_check && ! base_alias_check (x_addr, mem_addr)) return 0; /* If X is an unchanging read, then it can't possibly conflict with any non-unchanging store. It may conflict with an unchanging write though, because there may be a single store to this address to initialize it. Just fall through to the code below to resolve the case where we have both an unchanging read and an unchanging write. This won't handle all cases optimally, but the possible performance loss should be negligible. */ if (RTX_UNCHANGING_P (x) && ! RTX_UNCHANGING_P (mem)) return 0; x_addr = canon_rtx (x_addr); mem_addr = canon_rtx (mem_addr); if (mem_mode == VOIDmode) mem_mode = GET_MODE (mem); if (! memrefs_conflict_p (GET_MODE_SIZE (mem_mode), mem_addr, SIZE_FOR_MODE (x), x_addr, 0)) return 0; /* If both references are struct references, or both are not, nothing is known about aliasing. If either reference is QImode or BLKmode, ANSI C permits aliasing. If both addresses are constant, or both are not, nothing is known about aliasing. */ if (MEM_IN_STRUCT_P (x) == MEM_IN_STRUCT_P (mem) || mem_mode == QImode || mem_mode == BLKmode || GET_MODE (x) == QImode || GET_MODE (x) == BLKmode || GET_CODE (x_addr) == AND || GET_CODE (mem_addr) == AND || varies (x_addr) == varies (mem_addr)) return 1; /* One memory reference is to a constant address, one is not. One is to a structure, the other is not. If either memory reference is a variable structure the other is a fixed scalar and there is no aliasing. */ if ((MEM_IN_STRUCT_P (mem) && varies (mem_addr)) || (MEM_IN_STRUCT_P (x) && varies (x_addr))) return 0; return 1; } /* Anti dependence: X is written after read in MEM takes place. */ int anti_dependence (mem, x) rtx mem; rtx x; { if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem)) return 1; if (flag_alias_check && ! base_alias_check (XEXP (x, 0), XEXP (mem, 0))) return 0; /* If MEM is an unchanging read, then it can't possibly conflict with the store to X, because there is at most one store to MEM, and it must have occurred somewhere before MEM. */ x = canon_rtx (x); mem = canon_rtx (mem); if (RTX_UNCHANGING_P (mem)) return 0; return (memrefs_conflict_p (SIZE_FOR_MODE (mem), XEXP (mem, 0), SIZE_FOR_MODE (x), XEXP (x, 0), 0) && ! (MEM_IN_STRUCT_P (mem) && rtx_addr_varies_p (mem) && GET_MODE (mem) != QImode && GET_CODE (XEXP (mem, 0)) != AND && ! MEM_IN_STRUCT_P (x) && ! rtx_addr_varies_p (x)) && ! (MEM_IN_STRUCT_P (x) && rtx_addr_varies_p (x) && GET_MODE (x) != QImode && GET_CODE (XEXP (x, 0)) != AND && ! MEM_IN_STRUCT_P (mem) && ! rtx_addr_varies_p (mem))); } /* Output dependence: X is written after store in MEM takes place. */ int output_dependence (mem, x) register rtx mem; register rtx x; { if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem)) return 1; if (flag_alias_check && !base_alias_check (XEXP (x, 0), XEXP (mem, 0))) return 0; x = canon_rtx (x); mem = canon_rtx (mem); return (memrefs_conflict_p (SIZE_FOR_MODE (mem), XEXP (mem, 0), SIZE_FOR_MODE (x), XEXP (x, 0), 0) && ! (MEM_IN_STRUCT_P (mem) && rtx_addr_varies_p (mem) && GET_MODE (mem) != QImode && GET_CODE (XEXP (mem, 0)) != AND && ! MEM_IN_STRUCT_P (x) && ! rtx_addr_varies_p (x)) && ! (MEM_IN_STRUCT_P (x) && rtx_addr_varies_p (x) && GET_MODE (x) != QImode && GET_CODE (XEXP (x, 0)) != AND && ! MEM_IN_STRUCT_P (mem) && ! rtx_addr_varies_p (mem))); } void init_alias_analysis () { int maxreg = max_reg_num (); int changed, pass; register int i; register rtx insn; rtx note; rtx set; reg_known_value_size = maxreg; reg_known_value = (rtx *) oballoc ((maxreg - FIRST_PSEUDO_REGISTER) * sizeof (rtx)) - FIRST_PSEUDO_REGISTER; reg_known_equiv_p = oballoc (maxreg - FIRST_PSEUDO_REGISTER) - FIRST_PSEUDO_REGISTER; bzero ((char *) (reg_known_value + FIRST_PSEUDO_REGISTER), (maxreg-FIRST_PSEUDO_REGISTER) * sizeof (rtx)); bzero (reg_known_equiv_p + FIRST_PSEUDO_REGISTER, (maxreg - FIRST_PSEUDO_REGISTER) * sizeof (char)); if (flag_alias_check) { /* Overallocate reg_base_value to allow some growth during loop optimization. Loop unrolling can create a large number of registers. */ reg_base_value_size = maxreg * 2; reg_base_value = (rtx *)oballoc (reg_base_value_size * sizeof (rtx)); new_reg_base_value = (rtx *)alloca (reg_base_value_size * sizeof (rtx)); reg_seen = (char *)alloca (reg_base_value_size); bzero ((char *) reg_base_value, reg_base_value_size * sizeof (rtx)); } /* The basic idea is that each pass through this loop will use the "constant" information from the previous pass to propagate alias information through another level of assignments. This could get expensive if the assignment chains are long. Maybe we should throttle the number of iterations, possibly based on the optimization level. We could propagate more information in the first pass by making use of REG_N_SETS to determine immediately that the alias information for a pseudo is "constant". A program with an uninitialized variable can cause an infinite loop here. Instead of doing a full dataflow analysis to detect such problems we just cap the number of iterations for the loop. The state of the arrays for the set chain in question does not matter since the program has undefined behavior. */ changed = 1; pass = 0; while (changed && pass < MAX_ALIAS_LOOP_PASSES) { /* Keep track of the pass number so we can break out of the loop. */ pass++; /* Assume nothing will change this iteration of the loop. */ changed = 0; /* We want to assign the same IDs each iteration of this loop, so start counting from zero each iteration of the loop. */ unique_id = 0; /* We're at the start of the funtion each iteration through the loop, so we're copying arguments. */ copying_arguments = 1; /* Only perform initialization of the arrays if we're actually performing alias analysis. */ if (flag_alias_check) { /* Wipe the potential alias information clean for this pass. */ bzero ((char *) new_reg_base_value, reg_base_value_size * sizeof (rtx)); /* Wipe the reg_seen array clean. */ bzero ((char *) reg_seen, reg_base_value_size); /* Mark all hard registers which may contain an address. The stack, frame and argument pointers may contain an address. An argument register which can hold a Pmode value may contain an address even if it is not in BASE_REGS. The address expression is VOIDmode for an argument and Pmode for other registers. */ #ifndef OUTGOING_REGNO #define OUTGOING_REGNO(N) N #endif for (i = 0; i < FIRST_PSEUDO_REGISTER; i++) /* Check whether this register can hold an incoming pointer argument. FUNCTION_ARG_REGNO_P tests outgoing register numbers, so translate if necessary due to register windows. */ if (FUNCTION_ARG_REGNO_P (OUTGOING_REGNO (i)) && HARD_REGNO_MODE_OK (i, Pmode)) new_reg_base_value[i] = gen_rtx (ADDRESS, VOIDmode, gen_rtx (REG, Pmode, i)); new_reg_base_value[STACK_POINTER_REGNUM] = gen_rtx (ADDRESS, Pmode, stack_pointer_rtx); new_reg_base_value[ARG_POINTER_REGNUM] = gen_rtx (ADDRESS, Pmode, arg_pointer_rtx); new_reg_base_value[FRAME_POINTER_REGNUM] = gen_rtx (ADDRESS, Pmode, frame_pointer_rtx); #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM new_reg_base_value[HARD_FRAME_POINTER_REGNUM] = gen_rtx (ADDRESS, Pmode, hard_frame_pointer_rtx); #endif if (struct_value_incoming_rtx && GET_CODE (struct_value_incoming_rtx) == REG) new_reg_base_value[REGNO (struct_value_incoming_rtx)] = gen_rtx (ADDRESS, Pmode, struct_value_incoming_rtx); if (static_chain_rtx && GET_CODE (static_chain_rtx) == REG) new_reg_base_value[REGNO (static_chain_rtx)] = gen_rtx (ADDRESS, Pmode, static_chain_rtx); } /* Walk the insns adding values to the new_reg_base_value array. */ for (insn = get_insns (); insn; insn = NEXT_INSN (insn)) { if (flag_alias_check && GET_RTX_CLASS (GET_CODE (insn)) == 'i') { /* If this insn has a noalias note, process it, Otherwise, scan for sets. A simple set will have no side effects which could change the base value of any other register. */ rtx noalias_note; if (GET_CODE (PATTERN (insn)) == SET && (noalias_note = find_reg_note (insn, REG_NOALIAS, NULL_RTX))) record_set (SET_DEST (PATTERN (insn)), 0); else note_stores (PATTERN (insn), record_set); } else if (GET_CODE (insn) == NOTE && NOTE_LINE_NUMBER (insn) == NOTE_INSN_FUNCTION_BEG) copying_arguments = 0; if ((set = single_set (insn)) != 0 && GET_CODE (SET_DEST (set)) == REG && REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER && (((note = find_reg_note (insn, REG_EQUAL, 0)) != 0 && REG_N_SETS (REGNO (SET_DEST (set))) == 1) || (note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) != 0) && GET_CODE (XEXP (note, 0)) != EXPR_LIST) { int regno = REGNO (SET_DEST (set)); reg_known_value[regno] = XEXP (note, 0); reg_known_equiv_p[regno] = REG_NOTE_KIND (note) == REG_EQUIV; } } /* Now propagate values from new_reg_base_value to reg_base_value. */ if (flag_alias_check) for (i = 0; i < reg_base_value_size; i++) { if (new_reg_base_value[i] && new_reg_base_value[i] != reg_base_value[i] && !rtx_equal_p (new_reg_base_value[i], reg_base_value[i])) { reg_base_value[i] = new_reg_base_value[i]; changed = 1; } } } /* Fill in the remaining entries. */ for (i = FIRST_PSEUDO_REGISTER; i < maxreg; i++) if (reg_known_value[i] == 0) reg_known_value[i] = regno_reg_rtx[i]; if (! flag_alias_check) return; /* Simplify the reg_base_value array so that no register refers to another register, except to special registers indirectly through ADDRESS expressions. In theory this loop can take as long as O(registers^2), but unless there are very long dependency chains it will run in close to linear time. This loop may not be needed any longer now that the main loop does a better job at propagating alias information. */ pass = 0; do { changed = 0; pass++; for (i = 0; i < reg_base_value_size; i++) { rtx base = reg_base_value[i]; if (base && GET_CODE (base) == REG) { int base_regno = REGNO (base); if (base_regno == i) /* register set from itself */ reg_base_value[i] = 0; else reg_base_value[i] = reg_base_value[base_regno]; changed = 1; } } } while (changed && pass < MAX_ALIAS_LOOP_PASSES); new_reg_base_value = 0; reg_seen = 0; } void end_alias_analysis () { reg_known_value = 0; reg_base_value = 0; reg_base_value_size = 0; }