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Diffstat (limited to 'gcc-4.9/gcc/compare-elim.c')
| -rw-r--r-- | gcc-4.9/gcc/compare-elim.c | 692 |
1 files changed, 692 insertions, 0 deletions
diff --git a/gcc-4.9/gcc/compare-elim.c b/gcc-4.9/gcc/compare-elim.c new file mode 100644 index 000000000..3fbe140b8 --- /dev/null +++ b/gcc-4.9/gcc/compare-elim.c @@ -0,0 +1,692 @@ +/* Post-reload compare elimination. + Copyright (C) 2010-2014 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 +<http://www.gnu.org/licenses/>. */ + +/* There is a set of targets whose general-purpose move or addition + instructions clobber the flags. These targets cannot split their + CBRANCH/CSTORE etc patterns before reload is complete, lest reload + itself insert these instructions in between the flags setter and user. + Because these targets cannot split the compare from the use, they + cannot make use of the comparison elimination offered by the combine pass. + + This is a small pass intended to provide comparison elimination similar to + what is available via NOTICE_UPDATE_CC for cc0 targets. This should help + encourage cc0 targets to convert to an explicit post-reload representation + of the flags. + + This pass assumes: + + (0) CBRANCH/CSTORE etc have been split in pass_split_after_reload. + + (1) All comparison patterns are represented as + + [(set (reg:CC) (compare:CC (reg) (immediate)))] + + (2) All insn patterns that modify the flags are represented as + + [(set (reg) (operation) + (clobber (reg:CC))] + + (3) If an insn of form (2) can usefully set the flags, there is + another pattern of the form + + [(set (reg) (operation) + (set (reg:CCM) (compare:CCM (operation) (immediate)))] + + The mode CCM will be chosen as if by SELECT_CC_MODE. + + Note that unlike NOTICE_UPDATE_CC, we do not handle memory operands. + This could be handled as a future enhancement. +*/ + +#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 "flags.h" +#include "basic-block.h" +#include "tree-pass.h" +#include "target.h" +#include "df.h" +#include "domwalk.h" + + +/* These structures describe a comparison and how it is used. */ + +/* The choice of maximum 3 uses comes from wanting to eliminate the two + duplicate compares from a three-way branch on the sign of a value. + This is also sufficient to eliminate the duplicate compare against the + high-part of a double-word comparison. */ +#define MAX_CMP_USE 3 + +struct comparison_use +{ + /* The instruction in which the result of the compare is used. */ + rtx insn; + /* The location of the flags register within the use. */ + rtx *loc; + /* The comparison code applied against the flags register. */ + enum rtx_code code; +}; + +struct comparison +{ + /* The comparison instruction. */ + rtx insn; + + /* The insn prior to the comparison insn that clobbers the flags. */ + rtx prev_clobber; + + /* The two values being compared. These will be either REGs or + constants. */ + rtx in_a, in_b; + + /* Information about how this comparison is used. */ + struct comparison_use uses[MAX_CMP_USE]; + + /* The original CC_MODE for this comparison. */ + enum machine_mode orig_mode; + + /* The number of uses identified for this comparison. */ + unsigned short n_uses; + + /* True if not all uses of this comparison have been identified. + This can happen either for overflowing the array above, or if + the flags register is used in some unusual context. */ + bool missing_uses; + + /* True if its inputs are still valid at the end of the block. */ + bool inputs_valid; +}; + +typedef struct comparison *comparison_struct_p; + +static vec<comparison_struct_p> all_compares; + +/* Look for a "conforming" comparison, as defined above. If valid, return + the rtx for the COMPARE itself. */ + +static rtx +conforming_compare (rtx insn) +{ + rtx set, src, dest; + + set = single_set (insn); + if (set == NULL) + return NULL; + + src = SET_SRC (set); + if (GET_CODE (src) != COMPARE) + return NULL; + + dest = SET_DEST (set); + if (!REG_P (dest) || REGNO (dest) != targetm.flags_regnum) + return NULL; + + if (REG_P (XEXP (src, 0)) + && REG_P (XEXP (src, 0)) + && (REG_P (XEXP (src, 1)) || CONSTANT_P (XEXP (src, 1)))) + return src; + + return NULL; +} + +/* Look for a pattern of the "correct" form for an insn with a flags clobber + for which we may be able to eliminate a compare later. We're not looking + to validate any inputs at this time, merely see that the basic shape is + correct. The term "arithmetic" may be somewhat misleading... */ + +static bool +arithmetic_flags_clobber_p (rtx insn) +{ + rtx pat, x; + + if (!NONJUMP_INSN_P (insn)) + return false; + pat = PATTERN (insn); + if (extract_asm_operands (pat)) + return false; + + if (GET_CODE (pat) == PARALLEL && XVECLEN (pat, 0) == 2) + { + x = XVECEXP (pat, 0, 0); + if (GET_CODE (x) != SET) + return false; + x = SET_DEST (x); + if (!REG_P (x)) + return false; + + x = XVECEXP (pat, 0, 1); + if (GET_CODE (x) == CLOBBER) + { + x = XEXP (x, 0); + if (REG_P (x) && REGNO (x) == targetm.flags_regnum) + return true; + } + } + + return false; +} + +/* Look for uses of FLAGS in INSN. If we find one we can analyze, record + it in CMP; otherwise indicate that we've missed a use. */ + +static void +find_flags_uses_in_insn (struct comparison *cmp, rtx insn) +{ + df_ref *use_rec, use; + + /* If we've already lost track of uses, don't bother collecting more. */ + if (cmp->missing_uses) + return; + + /* Find a USE of the flags register. */ + for (use_rec = DF_INSN_USES (insn); (use = *use_rec) != NULL; use_rec++) + if (DF_REF_REGNO (use) == targetm.flags_regnum) + { + rtx x, *loc; + + /* If this is an unusual use, quit. */ + if (DF_REF_TYPE (use) != DF_REF_REG_USE) + goto fail; + + /* If we've run out of slots to record uses, quit. */ + if (cmp->n_uses == MAX_CMP_USE) + goto fail; + + /* Unfortunately the location of the flags register, while present + in the reference structure, doesn't help. We need to find the + comparison code that is outer to the actual flags use. */ + loc = DF_REF_LOC (use); + x = PATTERN (insn); + if (GET_CODE (x) == PARALLEL) + x = XVECEXP (x, 0, 0); + x = SET_SRC (x); + if (GET_CODE (x) == IF_THEN_ELSE) + x = XEXP (x, 0); + if (COMPARISON_P (x) + && loc == &XEXP (x, 0) + && XEXP (x, 1) == const0_rtx) + { + /* We've found a use of the flags that we understand. */ + struct comparison_use *cuse = &cmp->uses[cmp->n_uses++]; + cuse->insn = insn; + cuse->loc = loc; + cuse->code = GET_CODE (x); + } + else + goto fail; + } + return; + + fail: + /* We failed to recognize this use of the flags register. */ + cmp->missing_uses = true; +} + +class find_comparison_dom_walker : public dom_walker +{ +public: + find_comparison_dom_walker (cdi_direction direction) + : dom_walker (direction) {} + + virtual void before_dom_children (basic_block); +}; + +/* Identify comparison instructions within BB. If the flags from the last + compare in the BB is live at the end of the block, install the compare + in BB->AUX. Called via dom_walker.walk (). */ + +void +find_comparison_dom_walker::before_dom_children (basic_block bb) +{ + struct comparison *last_cmp; + rtx insn, next, last_clobber; + bool last_cmp_valid; + bitmap killed; + + killed = BITMAP_ALLOC (NULL); + + /* The last comparison that was made. Will be reset to NULL + once the flags are clobbered. */ + last_cmp = NULL; + + /* True iff the last comparison has not been clobbered, nor + have its inputs. Used to eliminate duplicate compares. */ + last_cmp_valid = false; + + /* The last insn that clobbered the flags, if that insn is of + a form that may be valid for eliminating a following compare. + To be reset to NULL once the flags are set otherwise. */ + last_clobber = NULL; + + /* Propagate the last live comparison throughout the extended basic block. */ + if (single_pred_p (bb)) + { + last_cmp = (struct comparison *) single_pred (bb)->aux; + if (last_cmp) + last_cmp_valid = last_cmp->inputs_valid; + } + + for (insn = BB_HEAD (bb); insn; insn = next) + { + rtx src; + + next = (insn == BB_END (bb) ? NULL_RTX : NEXT_INSN (insn)); + if (!NONDEBUG_INSN_P (insn)) + continue; + + /* Compute the set of registers modified by this instruction. */ + bitmap_clear (killed); + df_simulate_find_defs (insn, killed); + + src = conforming_compare (insn); + if (src) + { + enum machine_mode src_mode = GET_MODE (src); + + /* Eliminate a compare that's redundant with the previous. */ + if (last_cmp_valid + && rtx_equal_p (last_cmp->in_a, XEXP (src, 0)) + && rtx_equal_p (last_cmp->in_b, XEXP (src, 1))) + { + rtx flags, x; + enum machine_mode new_mode + = targetm.cc_modes_compatible (last_cmp->orig_mode, src_mode); + + /* New mode is incompatible with the previous compare mode. */ + if (new_mode == VOIDmode) + continue; + + if (new_mode != last_cmp->orig_mode) + { + flags = gen_rtx_REG (src_mode, targetm.flags_regnum); + + /* Generate new comparison for substitution. */ + x = gen_rtx_COMPARE (new_mode, XEXP (src, 0), XEXP (src, 1)); + x = gen_rtx_SET (VOIDmode, flags, x); + + if (!validate_change (last_cmp->insn, + &PATTERN (last_cmp->insn), x, false)) + continue; + + last_cmp->orig_mode = new_mode; + } + + delete_insn (insn); + continue; + } + + last_cmp = XCNEW (struct comparison); + last_cmp->insn = insn; + last_cmp->prev_clobber = last_clobber; + last_cmp->in_a = XEXP (src, 0); + last_cmp->in_b = XEXP (src, 1); + last_cmp->orig_mode = src_mode; + all_compares.safe_push (last_cmp); + + /* It's unusual, but be prepared for comparison patterns that + also clobber an input, or perhaps a scratch. */ + last_clobber = NULL; + last_cmp_valid = true; + } + + /* Notice if this instruction kills the flags register. */ + else if (bitmap_bit_p (killed, targetm.flags_regnum)) + { + /* See if this insn could be the "clobber" that eliminates + a future comparison. */ + last_clobber = (arithmetic_flags_clobber_p (insn) ? insn : NULL); + + /* In either case, the previous compare is no longer valid. */ + last_cmp = NULL; + last_cmp_valid = false; + continue; + } + + /* Notice if this instruction uses the flags register. */ + else if (last_cmp) + find_flags_uses_in_insn (last_cmp, insn); + + /* Notice if any of the inputs to the comparison have changed. */ + if (last_cmp_valid + && (bitmap_bit_p (killed, REGNO (last_cmp->in_a)) + || (REG_P (last_cmp->in_b) + && bitmap_bit_p (killed, REGNO (last_cmp->in_b))))) + last_cmp_valid = false; + } + + BITMAP_FREE (killed); + + /* Remember the live comparison for subsequent members of + the extended basic block. */ + if (last_cmp) + { + bb->aux = last_cmp; + last_cmp->inputs_valid = last_cmp_valid; + + /* Look to see if the flags register is live outgoing here, and + incoming to any successor not part of the extended basic block. */ + if (bitmap_bit_p (df_get_live_out (bb), targetm.flags_regnum)) + { + edge e; + edge_iterator ei; + + FOR_EACH_EDGE (e, ei, bb->succs) + { + basic_block dest = e->dest; + if (bitmap_bit_p (df_get_live_in (bb), + targetm.flags_regnum) + && !single_pred_p (dest)) + { + last_cmp->missing_uses = true; + break; + } + } + } + } +} + +/* Find all comparisons in the function. */ + +static void +find_comparisons (void) +{ + calculate_dominance_info (CDI_DOMINATORS); + + find_comparison_dom_walker (CDI_DOMINATORS) + .walk (cfun->cfg->x_entry_block_ptr); + + clear_aux_for_blocks (); + free_dominance_info (CDI_DOMINATORS); +} + +/* Select an alternate CC_MODE for a comparison insn comparing A and B. + Note that inputs are almost certainly different than the IN_A and IN_B + stored in CMP -- we're called while attempting to eliminate the compare + after all. Return the new FLAGS rtx if successful, else return NULL. + Note that this function may start a change group. */ + +static rtx +maybe_select_cc_mode (struct comparison *cmp, rtx a ATTRIBUTE_UNUSED, + rtx b ATTRIBUTE_UNUSED) +{ + enum machine_mode sel_mode; + const int n = cmp->n_uses; + rtx flags = NULL; + +#ifndef SELECT_CC_MODE + /* Minimize code differences when this target macro is undefined. */ + return NULL; +#define SELECT_CC_MODE(A,B,C) (gcc_unreachable (), VOIDmode) +#endif + + /* If we don't have access to all of the uses, we can't validate. */ + if (cmp->missing_uses || n == 0) + return NULL; + + /* Find a new mode that works for all of the uses. Special case the + common case of exactly one use. */ + if (n == 1) + { + sel_mode = SELECT_CC_MODE (cmp->uses[0].code, a, b); + if (sel_mode != cmp->orig_mode) + { + flags = gen_rtx_REG (sel_mode, targetm.flags_regnum); + validate_change (cmp->uses[0].insn, cmp->uses[0].loc, flags, true); + } + } + else + { + int i; + + sel_mode = SELECT_CC_MODE (cmp->uses[0].code, a, b); + for (i = 1; i < n; ++i) + { + enum machine_mode new_mode; + new_mode = SELECT_CC_MODE (cmp->uses[i].code, a, b); + if (new_mode != sel_mode) + { + sel_mode = targetm.cc_modes_compatible (sel_mode, new_mode); + if (sel_mode == VOIDmode) + return NULL; + } + } + + if (sel_mode != cmp->orig_mode) + { + flags = gen_rtx_REG (sel_mode, targetm.flags_regnum); + for (i = 0; i < n; ++i) + validate_change (cmp->uses[i].insn, cmp->uses[i].loc, flags, true); + } + } + + return flags; +} + +/* Attempt to replace a comparison with a prior arithmetic insn that can + compute the same flags value as the comparison itself. Return true if + successful, having made all rtl modifications necessary. */ + +static bool +try_eliminate_compare (struct comparison *cmp) +{ + rtx x, insn, bb_head, flags, in_a, cmp_src; + + /* We must have found an interesting "clobber" preceding the compare. */ + if (cmp->prev_clobber == NULL) + return false; + + /* ??? For the moment we don't handle comparisons for which IN_B + is a register. We accepted these during initial comparison + recognition in order to eliminate duplicate compares. + An improvement here would be to handle x = a - b; if (a cmp b). */ + if (!CONSTANT_P (cmp->in_b)) + return false; + + /* Verify that IN_A is not clobbered in between CMP and PREV_CLOBBER. + Given that this target requires this pass, we can assume that most + insns do clobber the flags, and so the distance between the compare + and the clobber is likely to be small. */ + /* ??? This is one point at which one could argue that DF_REF_CHAIN would + be useful, but it is thought to be too heavy-weight a solution here. */ + + in_a = cmp->in_a; + insn = cmp->insn; + bb_head = BB_HEAD (BLOCK_FOR_INSN (insn)); + for (insn = PREV_INSN (insn); + insn != cmp->prev_clobber; + insn = PREV_INSN (insn)) + { + const int abnormal_flags + = (DF_REF_CONDITIONAL | DF_REF_PARTIAL | DF_REF_MAY_CLOBBER + | DF_REF_MUST_CLOBBER | DF_REF_SIGN_EXTRACT + | DF_REF_ZERO_EXTRACT | DF_REF_STRICT_LOW_PART + | DF_REF_PRE_POST_MODIFY); + df_ref *def_rec, def; + + /* Note that the BB_HEAD is always either a note or a label, but in + any case it means that IN_A is defined outside the block. */ + if (insn == bb_head) + return false; + if (NOTE_P (insn) || DEBUG_INSN_P (insn)) + continue; + + /* Find a possible def of IN_A in INSN. */ + for (def_rec = DF_INSN_DEFS (insn); (def = *def_rec) != NULL; def_rec++) + if (DF_REF_REGNO (def) == REGNO (in_a)) + break; + + /* No definitions of IN_A; continue searching. */ + if (def == NULL) + continue; + + /* Bail if this is not a totally normal set of IN_A. */ + if (DF_REF_IS_ARTIFICIAL (def)) + return false; + if (DF_REF_FLAGS (def) & abnormal_flags) + return false; + + /* We've found an insn between the compare and the clobber that sets + IN_A. Given that pass_cprop_hardreg has not yet run, we still find + situations in which we can usefully look through a copy insn. */ + x = single_set (insn); + if (x == NULL) + return false; + in_a = SET_SRC (x); + if (!REG_P (in_a)) + return false; + } + + /* We've reached PREV_CLOBBER without finding a modification of IN_A. + Validate that PREV_CLOBBER itself does in fact refer to IN_A. Do + recall that we've already validated the shape of PREV_CLOBBER. */ + x = XVECEXP (PATTERN (insn), 0, 0); + if (rtx_equal_p (SET_DEST (x), in_a)) + cmp_src = SET_SRC (x); + + /* Also check operations with implicit extensions, e.g.: + [(set (reg:DI) + (zero_extend:DI (plus:SI (reg:SI)(reg:SI)))) + (set (reg:CCZ flags) + (compare:CCZ + (plus:SI (reg:SI)(reg:SI)) + (const_int 0)))] */ + else if (REG_P (SET_DEST (x)) + && REG_P (in_a) + && REGNO (SET_DEST (x)) == REGNO (in_a) + && (GET_CODE (SET_SRC (x)) == ZERO_EXTEND + || GET_CODE (SET_SRC (x)) == SIGN_EXTEND) + && GET_MODE (XEXP (SET_SRC (x), 0)) == GET_MODE (in_a)) + cmp_src = XEXP (SET_SRC (x), 0); + else + return false; + + /* Determine if we ought to use a different CC_MODE here. */ + flags = maybe_select_cc_mode (cmp, cmp_src, cmp->in_b); + if (flags == NULL) + flags = gen_rtx_REG (cmp->orig_mode, targetm.flags_regnum); + + /* Generate a new comparison for installation in the setter. */ + x = copy_rtx (cmp_src); + x = gen_rtx_COMPARE (GET_MODE (flags), x, cmp->in_b); + x = gen_rtx_SET (VOIDmode, flags, x); + + /* Succeed if the new instruction is valid. Note that we may have started + a change group within maybe_select_cc_mode, therefore we must continue. */ + validate_change (insn, &XVECEXP (PATTERN (insn), 0, 1), x, true); + if (!apply_change_group ()) + return false; + + /* Success. Delete the compare insn... */ + delete_insn (cmp->insn); + + /* ... and any notes that are now invalid due to multiple sets. */ + x = find_regno_note (insn, REG_UNUSED, targetm.flags_regnum); + if (x) + remove_note (insn, x); + x = find_reg_note (insn, REG_EQUAL, NULL); + if (x) + remove_note (insn, x); + x = find_reg_note (insn, REG_EQUIV, NULL); + if (x) + remove_note (insn, x); + + return true; +} + +/* Main entry point to the pass. */ + +static unsigned int +execute_compare_elim_after_reload (void) +{ + df_analyze (); + + gcc_checking_assert (!all_compares.exists ()); + + /* Locate all comparisons and their uses, and eliminate duplicates. */ + find_comparisons (); + if (all_compares.exists ()) + { + struct comparison *cmp; + size_t i; + + /* Eliminate comparisons that are redundant with flags computation. */ + FOR_EACH_VEC_ELT (all_compares, i, cmp) + { + try_eliminate_compare (cmp); + XDELETE (cmp); + } + + all_compares.release (); + } + + return 0; +} + +static bool +gate_compare_elim_after_reload (void) +{ + /* Setting this target hook value is how a backend indicates the need. */ + if (targetm.flags_regnum == INVALID_REGNUM) + return false; + return flag_compare_elim_after_reload; +} + +namespace { + +const pass_data pass_data_compare_elim_after_reload = +{ + RTL_PASS, /* type */ + "cmpelim", /* name */ + OPTGROUP_NONE, /* optinfo_flags */ + true, /* has_gate */ + true, /* has_execute */ + TV_NONE, /* tv_id */ + 0, /* properties_required */ + 0, /* properties_provided */ + 0, /* properties_destroyed */ + 0, /* todo_flags_start */ + ( TODO_df_finish | TODO_df_verify + | TODO_verify_rtl_sharing ), /* todo_flags_finish */ +}; + +class pass_compare_elim_after_reload : public rtl_opt_pass +{ +public: + pass_compare_elim_after_reload (gcc::context *ctxt) + : rtl_opt_pass (pass_data_compare_elim_after_reload, ctxt) + {} + + /* opt_pass methods: */ + bool gate () { return gate_compare_elim_after_reload (); } + unsigned int execute () { return execute_compare_elim_after_reload (); } + +}; // class pass_compare_elim_after_reload + +} // anon namespace + +rtl_opt_pass * +make_pass_compare_elim_after_reload (gcc::context *ctxt) +{ + return new pass_compare_elim_after_reload (ctxt); +} |