/* Combine stack adjustments. Copyright (C) 1987-2014 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as a sub/mov pair due to restrictions in calls.c. Propagation stops when any of the insns that need adjusting are (a) no longer valid because we've exceeded their range, (b) a non-trivial push instruction, or (c) a call instruction.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 "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 "reload.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 two kinds of stack references between stack adjusting instructions: stack references in memory addresses for regular insns and all stack references for debug insns. */ struct csa_reflist { HOST_WIDE_INT sp_offset; rtx insn, *ref; struct csa_reflist *next; }; static int stack_memref_p (rtx); static rtx single_set_for_csa (rtx); static void free_csa_reflist (struct csa_reflist *); static struct csa_reflist *record_one_stack_ref (rtx, rtx *, struct csa_reflist *); static int try_apply_stack_adjustment (rtx, struct csa_reflist *, HOST_WIDE_INT, HOST_WIDE_INT); static void combine_stack_adjustments_for_block (basic_block); static int record_stack_refs (rtx *, void *); /* Main entry point for stack adjustment combination. */ static void combine_stack_adjustments (void) { basic_block bb; FOR_EACH_BB_FN (bb, cfun) 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 && CONST_INT_P (XEXP (x, 1))) 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_reflist nodes. */ static void free_csa_reflist (struct csa_reflist *reflist) { struct csa_reflist *next; for (; reflist ; reflist = next) { next = reflist->next; free (reflist); } } /* Create a new csa_reflist node from the given stack reference. It is already known that the reference is either a MEM satisfying the predicate stack_memref_p or a REG representing the stack pointer. */ static struct csa_reflist * record_one_stack_ref (rtx insn, rtx *ref, struct csa_reflist *next_reflist) { struct csa_reflist *ml; ml = XNEW (struct csa_reflist); if (REG_P (*ref) || XEXP (*ref, 0) == stack_pointer_rtx) ml->sp_offset = 0; else ml->sp_offset = INTVAL (XEXP (XEXP (*ref, 0), 1)); ml->insn = insn; ml->ref = ref; ml->next = next_reflist; return ml; } /* Attempt to apply ADJUST to the stack adjusting insn INSN, as well as each of the memories and stack references in REFLIST. Return true on success. */ static int try_apply_stack_adjustment (rtx insn, struct csa_reflist *reflist, HOST_WIDE_INT new_adjust, HOST_WIDE_INT delta) { struct csa_reflist *ml; rtx set; set = single_set_for_csa (insn); if (MEM_P (SET_DEST (set))) validate_change (insn, &SET_DEST (set), replace_equiv_address (SET_DEST (set), stack_pointer_rtx), 1); else validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust), 1); for (ml = reflist; ml ; ml = ml->next) { rtx new_addr = plus_constant (Pmode, stack_pointer_rtx, ml->sp_offset - delta); rtx new_val; if (MEM_P (*ml->ref)) new_val = replace_equiv_address_nv (*ml->ref, new_addr); else if (GET_MODE (*ml->ref) == GET_MODE (stack_pointer_rtx)) new_val = new_addr; else new_val = lowpart_subreg (GET_MODE (*ml->ref), new_addr, GET_MODE (new_addr)); validate_change (ml->insn, ml->ref, new_val, 1); } if (apply_change_group ()) { /* Succeeded. Update our knowledge of the stack references. */ for (ml = reflist; 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 and other references in the insn and discard all other stack pointer references. */ struct record_stack_refs_data { rtx insn; struct csa_reflist *reflist; }; static int record_stack_refs (rtx *xp, void *data) { rtx x = *xp; struct record_stack_refs_data *d = (struct record_stack_refs_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->reflist = record_one_stack_ref (d->insn, xp, d->reflist); return -1; } /* Try harder for DEBUG_INSNs, handle e.g. (mem (mem (sp + 16) + 4). */ return !DEBUG_INSN_P (d->insn); 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. In DEBUG_INSNs, we want to replace all occurrences, otherwise they will cause -fcompare-debug failures. */ if (REGNO (x) == STACK_POINTER_REGNUM) { if (!DEBUG_INSN_P (d->insn)) return 1; d->reflist = record_one_stack_ref (d->insn, xp, d->reflist); return -1; } break; default: break; } return 0; } /* If INSN has a REG_ARGS_SIZE note, move it to LAST. AFTER is true iff LAST follows INSN in the instruction stream. */ static void maybe_move_args_size_note (rtx last, rtx insn, bool after) { rtx note, last_note; note = find_reg_note (insn, REG_ARGS_SIZE, NULL_RTX); if (note == NULL) return; last_note = find_reg_note (last, REG_ARGS_SIZE, NULL_RTX); if (last_note) { /* The ARGS_SIZE notes are *not* cumulative. They represent an absolute value, and the "most recent" note wins. */ if (!after) XEXP (last_note, 0) = XEXP (note, 0); } else add_reg_note (last, REG_ARGS_SIZE, XEXP (note, 0)); } /* Return the next (or previous) active insn within BB. */ static rtx prev_active_insn_bb (basic_block bb, rtx insn) { for (insn = PREV_INSN (insn); insn != PREV_INSN (BB_HEAD (bb)); insn = PREV_INSN (insn)) if (active_insn_p (insn)) return insn; return NULL_RTX; } static rtx next_active_insn_bb (basic_block bb, rtx insn) { for (insn = NEXT_INSN (insn); insn != NEXT_INSN (BB_END (bb)); insn = NEXT_INSN (insn)) if (active_insn_p (insn)) return insn; return NULL_RTX; } /* If INSN has a REG_ARGS_SIZE note, if possible move it to PREV. Otherwise search for a nearby candidate within BB where we can stick the note. */ static void force_move_args_size_note (basic_block bb, rtx prev, rtx insn) { rtx note, test, next_candidate, prev_candidate; /* If PREV exists, tail-call to the logic in the other function. */ if (prev) { maybe_move_args_size_note (prev, insn, false); return; } /* First, make sure there's anything that needs doing. */ note = find_reg_note (insn, REG_ARGS_SIZE, NULL_RTX); if (note == NULL) return; /* We need to find a spot between the previous and next exception points where we can place the note and "properly" deallocate the arguments. */ next_candidate = prev_candidate = NULL; /* It is often the case that we have insns in the order: call add sp (previous deallocation) sub sp (align for next arglist) push arg and the add/sub cancel. Therefore we begin by searching forward. */ test = insn; while ((test = next_active_insn_bb (bb, test)) != NULL) { /* Found an existing note: nothing to do. */ if (find_reg_note (test, REG_ARGS_SIZE, NULL_RTX)) return; /* Found something that affects unwinding. Stop searching. */ if (CALL_P (test) || !insn_nothrow_p (test)) break; if (next_candidate == NULL) next_candidate = test; } test = insn; while ((test = prev_active_insn_bb (bb, test)) != NULL) { rtx tnote; /* Found a place that seems logical to adjust the stack. */ tnote = find_reg_note (test, REG_ARGS_SIZE, NULL_RTX); if (tnote) { XEXP (tnote, 0) = XEXP (note, 0); return; } if (prev_candidate == NULL) prev_candidate = test; /* Found something that affects unwinding. Stop searching. */ if (CALL_P (test) || !insn_nothrow_p (test)) break; } if (prev_candidate) test = prev_candidate; else if (next_candidate) test = next_candidate; else { /* ??? We *must* have a place, lest we ICE on the lost adjustment. Options are: dummy clobber insn, nop, or prevent the removal of the sp += 0 insn. */ /* TODO: Find another way to indicate to the dwarf2 code that we have not in fact lost an adjustment. */ test = emit_insn_before (gen_rtx_CLOBBER (VOIDmode, const0_rtx), insn); } add_reg_note (test, REG_ARGS_SIZE, XEXP (note, 0)); } /* 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; rtx last2_sp_set = NULL_RTX; struct csa_reflist *reflist = NULL; rtx insn, next, set; struct record_stack_refs_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 && CONST_INT_P (XEXP (src, 1))) { 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 refs 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, reflist, last_sp_adjust + this_adjust, this_adjust)) { /* It worked! */ maybe_move_args_size_note (last_sp_set, insn, false); 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, reflist, last_sp_adjust + this_adjust, -last_sp_adjust)) { /* It worked! */ maybe_move_args_size_note (insn, last_sp_set, true); delete_insn (last_sp_set); last_sp_set = insn; last_sp_adjust += this_adjust; free_csa_reflist (reflist); reflist = 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) { if (last_sp_adjust == 0) { maybe_move_args_size_note (insn, last_sp_set, true); delete_insn (last_sp_set); } else last2_sp_set = last_sp_set; } free_csa_reflist (reflist); reflist = NULL; last_sp_set = insn; last_sp_adjust = this_adjust; continue; } /* Find a store with pre-(dec|inc)rement or pre-modify of exactly the previous adjustment and turn it into a simple store. This is equivalent to anticipating the stack adjustment so this must be an allocation. */ if (MEM_P (dest) && ((STACK_GROWS_DOWNWARD ? (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_INC && last_sp_adjust == -(HOST_WIDE_INT) GET_MODE_SIZE (GET_MODE (dest)))) || ((STACK_GROWS_DOWNWARD ? last_sp_adjust >= 0 : last_sp_adjust <= 0) && 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) && try_apply_stack_adjustment (insn, reflist, 0, -last_sp_adjust)) { if (last2_sp_set) maybe_move_args_size_note (last2_sp_set, last_sp_set, false); else maybe_move_args_size_note (insn, last_sp_set, true); delete_insn (last_sp_set); free_csa_reflist (reflist); reflist = NULL; last_sp_set = NULL_RTX; last_sp_adjust = 0; continue; } } data.insn = insn; data.reflist = reflist; if (!CALL_P (insn) && last_sp_set && !for_each_rtx (&PATTERN (insn), record_stack_refs, &data)) { reflist = data.reflist; continue; } reflist = data.reflist; /* 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) { force_move_args_size_note (bb, last2_sp_set, last_sp_set); delete_insn (last_sp_set); } free_csa_reflist (reflist); reflist = NULL; last2_sp_set = NULL_RTX; last_sp_set = NULL_RTX; last_sp_adjust = 0; } } if (last_sp_set && last_sp_adjust == 0) { force_move_args_size_note (bb, last2_sp_set, last_sp_set); delete_insn (last_sp_set); } if (reflist) free_csa_reflist (reflist); } static unsigned int rest_of_handle_stack_adjustments (void) { df_note_add_problem (); df_analyze (); combine_stack_adjustments (); return 0; } namespace { const pass_data pass_data_stack_adjustments = { RTL_PASS, /* type */ "csa", /* name */ OPTGROUP_NONE, /* optinfo_flags */ TV_COMBINE_STACK_ADJUST, /* tv_id */ 0, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_df_finish, /* todo_flags_finish */ }; class pass_stack_adjustments : public rtl_opt_pass { public: pass_stack_adjustments (gcc::context *ctxt) : rtl_opt_pass (pass_data_stack_adjustments, ctxt) {} /* opt_pass methods: */ virtual bool gate (function *); virtual unsigned int execute (function *) { return rest_of_handle_stack_adjustments (); } }; // class pass_stack_adjustments bool pass_stack_adjustments::gate (function *) { /* This is kind of a heuristic. We need to run combine_stack_adjustments even for machines with possibly nonzero TARGET_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) return false; #endif return flag_combine_stack_adjustments; } } // anon namespace rtl_opt_pass * make_pass_stack_adjustments (gcc::context *ctxt) { return new pass_stack_adjustments (ctxt); }