/* Combine stack adjustments. Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. This file is part of GCC. GCC 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 3, or (at your option) any later version. GCC 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 GCC; see the file COPYING3. If not see . */ /* Track stack adjustments and stack memory references. Attempt to reduce the number of stack adjustments by back-propagating across the memory references. This is intended primarily for use with targets that do not define ACCUMULATE_OUTGOING_ARGS. It is of significantly more value to targets that define PREFERRED_STACK_BOUNDARY more aligned than STACK_BOUNDARY (e.g. x86), or if not all registers can be pushed (e.g. x86 fp regs) which would ordinarily have to be implemented as a sub/mov pair due to restrictions in calls.c. Propagation stops when any of the insns that need adjusting are (a) no longer valid because we've exceeded their range, (b) a non-trivial push instruction, or (c) a call instruction. Restriction B is based on the assumption that push instructions are smaller or faster. If a port really wants to remove all pushes, it should have defined ACCUMULATE_OUTGOING_ARGS. The one exception that is made is for an add immediately followed by a push. */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "rtl.h" #include "tm_p.h" #include "insn-config.h" #include "recog.h" #include "output.h" #include "regs.h" #include "hard-reg-set.h" #include "flags.h" #include "function.h" #include "expr.h" #include "basic-block.h" #include "df.h" #include "except.h" #include "toplev.h" #include "reload.h" #include "timevar.h" #include "tree-pass.h" /* Turn STACK_GROWS_DOWNWARD into a boolean. */ #ifdef STACK_GROWS_DOWNWARD #undef STACK_GROWS_DOWNWARD #define STACK_GROWS_DOWNWARD 1 #else #define STACK_GROWS_DOWNWARD 0 #endif /* This structure records stack memory references between stack adjusting instructions. */ struct csa_memlist { HOST_WIDE_INT sp_offset; rtx insn, *mem; struct csa_memlist *next; }; static int stack_memref_p (rtx); static rtx single_set_for_csa (rtx); static void free_csa_memlist (struct csa_memlist *); static struct csa_memlist *record_one_stack_memref (rtx, rtx *, struct csa_memlist *); static int try_apply_stack_adjustment (rtx, struct csa_memlist *, HOST_WIDE_INT, HOST_WIDE_INT); static void combine_stack_adjustments_for_block (basic_block); static int record_stack_memrefs (rtx *, void *); /* Main entry point for stack adjustment combination. */ static void combine_stack_adjustments (void) { basic_block bb; FOR_EACH_BB (bb) combine_stack_adjustments_for_block (bb); } /* Recognize a MEM of the form (sp) or (plus sp const). */ static int stack_memref_p (rtx x) { if (!MEM_P (x)) return 0; x = XEXP (x, 0); if (x == stack_pointer_rtx) return 1; if (GET_CODE (x) == PLUS && XEXP (x, 0) == stack_pointer_rtx && GET_CODE (XEXP (x, 1)) == CONST_INT) return 1; return 0; } /* Recognize either normal single_set or the hack in i386.md for tying fp and sp adjustments. */ static rtx single_set_for_csa (rtx insn) { int i; rtx tmp = single_set (insn); if (tmp) return tmp; if (!NONJUMP_INSN_P (insn) || GET_CODE (PATTERN (insn)) != PARALLEL) return NULL_RTX; tmp = PATTERN (insn); if (GET_CODE (XVECEXP (tmp, 0, 0)) != SET) return NULL_RTX; for (i = 1; i < XVECLEN (tmp, 0); ++i) { rtx this_rtx = XVECEXP (tmp, 0, i); /* The special case is allowing a no-op set. */ if (GET_CODE (this_rtx) == SET && SET_SRC (this_rtx) == SET_DEST (this_rtx)) ; else if (GET_CODE (this_rtx) != CLOBBER && GET_CODE (this_rtx) != USE) return NULL_RTX; } return XVECEXP (tmp, 0, 0); } /* Free the list of csa_memlist nodes. */ static void free_csa_memlist (struct csa_memlist *memlist) { struct csa_memlist *next; for (; memlist ; memlist = next) { next = memlist->next; free (memlist); } } /* Create a new csa_memlist node from the given memory reference. It is already known that the memory is stack_memref_p. */ static struct csa_memlist * record_one_stack_memref (rtx insn, rtx *mem, struct csa_memlist *next_memlist) { struct csa_memlist *ml; ml = XNEW (struct csa_memlist); if (XEXP (*mem, 0) == stack_pointer_rtx) ml->sp_offset = 0; else ml->sp_offset = INTVAL (XEXP (XEXP (*mem, 0), 1)); ml->insn = insn; ml->mem = mem; ml->next = next_memlist; return ml; } /* Attempt to apply ADJUST to the stack adjusting insn INSN, as well as each of the memories in MEMLIST. Return true on success. */ static int try_apply_stack_adjustment (rtx insn, struct csa_memlist *memlist, HOST_WIDE_INT new_adjust, HOST_WIDE_INT delta) { struct csa_memlist *ml; rtx set; set = single_set_for_csa (insn); validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust), 1); for (ml = memlist; ml ; ml = ml->next) validate_change (ml->insn, ml->mem, replace_equiv_address_nv (*ml->mem, plus_constant (stack_pointer_rtx, ml->sp_offset - delta)), 1); if (apply_change_group ()) { /* Succeeded. Update our knowledge of the memory references. */ for (ml = memlist; ml ; ml = ml->next) ml->sp_offset -= delta; return 1; } else return 0; } /* Called via for_each_rtx and used to record all stack memory references in the insn and discard all other stack pointer references. */ struct record_stack_memrefs_data { rtx insn; struct csa_memlist *memlist; }; static int record_stack_memrefs (rtx *xp, void *data) { rtx x = *xp; struct record_stack_memrefs_data *d = (struct record_stack_memrefs_data *) data; if (!x) return 0; switch (GET_CODE (x)) { case MEM: if (!reg_mentioned_p (stack_pointer_rtx, x)) return -1; /* We are not able to handle correctly all possible memrefs containing stack pointer, so this check is necessary. */ if (stack_memref_p (x)) { d->memlist = record_one_stack_memref (d->insn, xp, d->memlist); return -1; } return 1; case REG: /* ??? We want be able to handle non-memory stack pointer references later. For now just discard all insns referring to stack pointer outside mem expressions. We would probably want to teach validate_replace to simplify expressions first. We can't just compare with STACK_POINTER_RTX because the reference to the stack pointer might be in some other mode. In particular, an explicit clobber in an asm statement will result in a QImode clobber. */ if (REGNO (x) == STACK_POINTER_REGNUM) return 1; break; default: break; } return 0; } /* Adjust or create REG_FRAME_RELATED_EXPR note when merging a stack adjustment into a frame related insn. */ static void adjust_frame_related_expr (rtx last_sp_set, rtx insn, HOST_WIDE_INT this_adjust) { rtx note = find_reg_note (last_sp_set, REG_FRAME_RELATED_EXPR, NULL_RTX); rtx new_expr = NULL_RTX; if (note == NULL_RTX && RTX_FRAME_RELATED_P (insn)) return; if (note && GET_CODE (XEXP (note, 0)) == SEQUENCE && XVECLEN (XEXP (note, 0), 0) >= 2) { rtx expr = XEXP (note, 0); rtx last = XVECEXP (expr, 0, XVECLEN (expr, 0) - 1); int i; if (GET_CODE (last) == SET && RTX_FRAME_RELATED_P (last) == RTX_FRAME_RELATED_P (insn) && SET_DEST (last) == stack_pointer_rtx && GET_CODE (SET_SRC (last)) == PLUS && XEXP (SET_SRC (last), 0) == stack_pointer_rtx && GET_CODE (XEXP (SET_SRC (last), 1)) == CONST_INT) { XEXP (SET_SRC (last), 1) = GEN_INT (INTVAL (XEXP (SET_SRC (last), 1)) + this_adjust); return; } new_expr = gen_rtx_SEQUENCE (VOIDmode, rtvec_alloc (XVECLEN (expr, 0) + 1)); for (i = 0; i < XVECLEN (expr, 0); i++) XVECEXP (new_expr, 0, i) = XVECEXP (expr, 0, i); } else { new_expr = gen_rtx_SEQUENCE (VOIDmode, rtvec_alloc (2)); if (note) XVECEXP (new_expr, 0, 0) = XEXP (note, 0); else { rtx expr = copy_rtx (single_set_for_csa (last_sp_set)); XEXP (SET_SRC (expr), 1) = GEN_INT (INTVAL (XEXP (SET_SRC (expr), 1)) - this_adjust); RTX_FRAME_RELATED_P (expr) = 1; XVECEXP (new_expr, 0, 0) = expr; } } XVECEXP (new_expr, 0, XVECLEN (new_expr, 0) - 1) = copy_rtx (single_set_for_csa (insn)); RTX_FRAME_RELATED_P (XVECEXP (new_expr, 0, XVECLEN (new_expr, 0) - 1)) = RTX_FRAME_RELATED_P (insn); if (note) XEXP (note, 0) = new_expr; else add_reg_note (last_sp_set, REG_FRAME_RELATED_EXPR, new_expr); } /* Subroutine of combine_stack_adjustments, called for each basic block. */ static void combine_stack_adjustments_for_block (basic_block bb) { HOST_WIDE_INT last_sp_adjust = 0; rtx last_sp_set = NULL_RTX; struct csa_memlist *memlist = NULL; rtx insn, next, set; struct record_stack_memrefs_data data; bool end_of_block = false; for (insn = BB_HEAD (bb); !end_of_block ; insn = next) { end_of_block = insn == BB_END (bb); next = NEXT_INSN (insn); if (! INSN_P (insn)) continue; set = single_set_for_csa (insn); if (set) { rtx dest = SET_DEST (set); rtx src = SET_SRC (set); /* Find constant additions to the stack pointer. */ if (dest == stack_pointer_rtx && GET_CODE (src) == PLUS && XEXP (src, 0) == stack_pointer_rtx && GET_CODE (XEXP (src, 1)) == CONST_INT) { HOST_WIDE_INT this_adjust = INTVAL (XEXP (src, 1)); /* If we've not seen an adjustment previously, record it now and continue. */ if (! last_sp_set) { last_sp_set = insn; last_sp_adjust = this_adjust; continue; } /* If not all recorded memrefs can be adjusted, or the adjustment is now too large for a constant addition, we cannot merge the two stack adjustments. Also we need to be careful to not move stack pointer such that we create stack accesses outside the allocated area. We can combine an allocation into the first insn, or a deallocation into the second insn. We can not combine an allocation followed by a deallocation. The only somewhat frequent occurrence of the later is when a function allocates a stack frame but does not use it. For this case, we would need to analyze rtl stream to be sure that allocated area is really unused. This means not only checking the memory references, but also all registers or global memory references possibly containing a stack frame address. Perhaps the best way to address this problem is to teach gcc not to allocate stack for objects never used. */ /* Combine an allocation into the first instruction. */ if (STACK_GROWS_DOWNWARD ? this_adjust <= 0 : this_adjust >= 0) { if (try_apply_stack_adjustment (last_sp_set, memlist, last_sp_adjust + this_adjust, this_adjust)) { if (RTX_FRAME_RELATED_P (last_sp_set)) adjust_frame_related_expr (last_sp_set, insn, this_adjust); /* It worked! */ delete_insn (insn); last_sp_adjust += this_adjust; continue; } } /* Otherwise we have a deallocation. Do not combine with a previous allocation. Combine into the second insn. */ else if (STACK_GROWS_DOWNWARD ? last_sp_adjust >= 0 : last_sp_adjust <= 0) { if (try_apply_stack_adjustment (insn, memlist, last_sp_adjust + this_adjust, -last_sp_adjust)) { /* It worked! */ delete_insn (last_sp_set); last_sp_set = insn; last_sp_adjust += this_adjust; free_csa_memlist (memlist); memlist = NULL; continue; } } /* Combination failed. Restart processing from here. If deallocation+allocation conspired to cancel, we can delete the old deallocation insn. */ if (last_sp_set && last_sp_adjust == 0) delete_insn (last_sp_set); free_csa_memlist (memlist); memlist = NULL; last_sp_set = insn; last_sp_adjust = this_adjust; continue; } /* Find a predecrement of exactly the previous adjustment and turn it into a direct store. Obviously we can't do this if there were any intervening uses of the stack pointer. */ if (memlist == NULL && MEM_P (dest) && ((GET_CODE (XEXP (dest, 0)) == PRE_DEC && (last_sp_adjust == (HOST_WIDE_INT) GET_MODE_SIZE (GET_MODE (dest)))) || (GET_CODE (XEXP (dest, 0)) == PRE_MODIFY && GET_CODE (XEXP (XEXP (dest, 0), 1)) == PLUS && XEXP (XEXP (XEXP (dest, 0), 1), 0) == stack_pointer_rtx && (GET_CODE (XEXP (XEXP (XEXP (dest, 0), 1), 1)) == CONST_INT) && (INTVAL (XEXP (XEXP (XEXP (dest, 0), 1), 1)) == -last_sp_adjust))) && XEXP (XEXP (dest, 0), 0) == stack_pointer_rtx && ! reg_mentioned_p (stack_pointer_rtx, src) && memory_address_p (GET_MODE (dest), stack_pointer_rtx) && validate_change (insn, &SET_DEST (set), replace_equiv_address (dest, stack_pointer_rtx), 0)) { delete_insn (last_sp_set); free_csa_memlist (memlist); memlist = NULL; last_sp_set = NULL_RTX; last_sp_adjust = 0; continue; } } data.insn = insn; data.memlist = memlist; if (!CALL_P (insn) && last_sp_set && !for_each_rtx (&PATTERN (insn), record_stack_memrefs, &data)) { memlist = data.memlist; continue; } memlist = data.memlist; /* Otherwise, we were not able to process the instruction. Do not continue collecting data across such a one. */ if (last_sp_set && (CALL_P (insn) || reg_mentioned_p (stack_pointer_rtx, PATTERN (insn)))) { if (last_sp_set && last_sp_adjust == 0) delete_insn (last_sp_set); free_csa_memlist (memlist); memlist = NULL; last_sp_set = NULL_RTX; last_sp_adjust = 0; } } if (last_sp_set && last_sp_adjust == 0) delete_insn (last_sp_set); if (memlist) free_csa_memlist (memlist); } static bool gate_handle_stack_adjustments (void) { return (optimize > 0); } static unsigned int rest_of_handle_stack_adjustments (void) { cleanup_cfg (flag_crossjumping ? CLEANUP_CROSSJUMP : 0); /* This is kind of a heuristic. We need to run combine_stack_adjustments even for machines with possibly nonzero RETURN_POPS_ARGS and ACCUMULATE_OUTGOING_ARGS. We expect that only ports having push instructions will have popping returns. */ #ifndef PUSH_ROUNDING if (!ACCUMULATE_OUTGOING_ARGS) #endif { df_note_add_problem (); df_analyze (); combine_stack_adjustments (); } return 0; } struct rtl_opt_pass pass_stack_adjustments = { { RTL_PASS, "csa", /* name */ gate_handle_stack_adjustments, /* gate */ rest_of_handle_stack_adjustments, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ 0, /* tv_id */ 0, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_df_finish | TODO_verify_rtl_sharing | TODO_dump_func | TODO_ggc_collect, /* todo_flags_finish */ } };