| /* Post-reload compare elimination. |
| Copyright (C) 2010-2021 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) (reg_or_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:CCM) (compare:CCM (operation) (immediate))) |
| (set (reg) (operation)] |
| |
| 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 "backend.h" |
| #include "target.h" |
| #include "rtl.h" |
| #include "df.h" |
| #include "memmodel.h" |
| #include "tm_p.h" |
| #include "insn-config.h" |
| #include "recog.h" |
| #include "emit-rtl.h" |
| #include "cfgrtl.h" |
| #include "tree-pass.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 *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 *insn; |
| |
| /* The insn prior to the comparison insn that clobbers the flags. */ |
| rtx_insn *prev_clobber; |
| |
| /* The insn prior to the comparison insn that sets in_a REG. */ |
| rtx_insn *in_a_setter; |
| |
| /* The two values being compared. These will be either REGs or |
| constants. */ |
| rtx in_a, in_b; |
| |
| /* The REG_EH_REGION of the comparison. */ |
| rtx eh_note; |
| |
| /* Information about how this comparison is used. */ |
| struct comparison_use uses[MAX_CMP_USE]; |
| |
| /* The original CC_MODE for this comparison. */ |
| 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; |
| |
| /* Whether IN_A is wrapped in a NOT before being compared. */ |
| bool not_in_a; |
| }; |
| |
| static vec<comparison *> all_compares; |
| |
| /* Return whether X is a NOT unary expression. */ |
| |
| static bool |
| is_not (rtx x) |
| { |
| return GET_CODE (x) == NOT; |
| } |
| |
| /* Strip a NOT unary expression around X, if any. */ |
| |
| static rtx |
| strip_not (rtx x) |
| { |
| if (is_not (x)) |
| return XEXP (x, 0); |
| |
| return x; |
| } |
| |
| /* Look for a "conforming" comparison, as defined above. If valid, return |
| the rtx for the COMPARE itself. */ |
| |
| static rtx |
| conforming_compare (rtx_insn *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 (strip_not (XEXP (src, 0)))) |
| return NULL; |
| |
| if (CONSTANT_P (XEXP (src, 1)) || REG_P (XEXP (src, 1))) |
| return src; |
| |
| if (GET_CODE (XEXP (src, 1)) == UNSPEC) |
| { |
| for (int i = 0; i < XVECLEN (XEXP (src, 1), 0); i++) |
| if (!REG_P (XVECEXP (XEXP (src, 1), 0, i))) |
| return NULL; |
| 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 *insn) |
| { |
| rtx pat, x; |
| |
| if (!NONJUMP_INSN_P (insn)) |
| return false; |
| pat = PATTERN (insn); |
| if (asm_noperands (pat) >= 0) |
| 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 *insn) |
| { |
| df_ref 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_EACH_INSN_USE (use, insn) |
| 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 edge before_dom_children (basic_block); |
| }; |
| |
| /* Return true if conforming COMPARE with EH_NOTE is redundant with comparison |
| CMP and can thus be eliminated. */ |
| |
| static bool |
| can_eliminate_compare (rtx compare, rtx eh_note, struct comparison *cmp) |
| { |
| /* Take care that it's in the same EH region. */ |
| if (cfun->can_throw_non_call_exceptions |
| && !rtx_equal_p (eh_note, cmp->eh_note)) |
| return false; |
| |
| /* Make sure the compare is redundant with the previous. */ |
| if (!rtx_equal_p (strip_not (XEXP (compare, 0)), cmp->in_a) |
| || !rtx_equal_p (XEXP (compare, 1), cmp->in_b)) |
| return false; |
| |
| if (is_not (XEXP (compare, 0)) != cmp->not_in_a) |
| return false; |
| |
| /* New mode must be compatible with the previous compare mode. */ |
| machine_mode new_mode |
| = targetm.cc_modes_compatible (GET_MODE (compare), cmp->orig_mode); |
| |
| if (new_mode == VOIDmode) |
| return false; |
| |
| if (cmp->orig_mode != new_mode) |
| { |
| /* Generate new comparison for substitution. */ |
| rtx flags = gen_rtx_REG (new_mode, targetm.flags_regnum); |
| rtx x = gen_rtx_COMPARE (new_mode, cmp->in_a, cmp->in_b); |
| x = gen_rtx_SET (flags, x); |
| |
| if (!validate_change (cmp->insn, &PATTERN (cmp->insn), x, false)) |
| return false; |
| |
| cmp->orig_mode = new_mode; |
| } |
| |
| return true; |
| } |
| |
| /* 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 (). */ |
| |
| edge |
| find_comparison_dom_walker::before_dom_children (basic_block bb) |
| { |
| rtx_insn *insn, *next; |
| bool need_purge = false; |
| rtx_insn *last_setter[FIRST_PSEUDO_REGISTER]; |
| |
| /* The last comparison that was made. Will be reset to NULL |
| once the flags are clobbered. */ |
| struct comparison *last_cmp = NULL; |
| |
| /* True iff the last comparison has not been clobbered, nor |
| have its inputs. Used to eliminate duplicate compares. */ |
| bool 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. */ |
| rtx_insn *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; |
| } |
| |
| memset (last_setter, 0, sizeof (last_setter)); |
| for (insn = BB_HEAD (bb); insn; insn = next) |
| { |
| rtx src; |
| |
| next = (insn == BB_END (bb) ? NULL : NEXT_INSN (insn)); |
| if (!NONDEBUG_INSN_P (insn)) |
| continue; |
| |
| src = conforming_compare (insn); |
| if (src) |
| { |
| rtx eh_note = NULL; |
| |
| if (cfun->can_throw_non_call_exceptions) |
| eh_note = find_reg_note (insn, REG_EH_REGION, NULL); |
| |
| if (last_cmp_valid && can_eliminate_compare (src, eh_note, last_cmp)) |
| { |
| if (eh_note) |
| need_purge = true; |
| delete_insn (insn); |
| continue; |
| } |
| |
| last_cmp = XCNEW (struct comparison); |
| last_cmp->insn = insn; |
| last_cmp->prev_clobber = last_clobber; |
| last_cmp->in_a = strip_not (XEXP (src, 0)); |
| last_cmp->in_b = XEXP (src, 1); |
| last_cmp->not_in_a = is_not (XEXP (src, 0)); |
| last_cmp->eh_note = eh_note; |
| last_cmp->orig_mode = GET_MODE (src); |
| if (last_cmp->in_b == const0_rtx |
| && last_setter[REGNO (last_cmp->in_a)]) |
| { |
| rtx set = single_set (last_setter[REGNO (last_cmp->in_a)]); |
| if (set && rtx_equal_p (SET_DEST (set), last_cmp->in_a)) |
| last_cmp->in_a_setter = last_setter[REGNO (last_cmp->in_a)]; |
| } |
| 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; |
| } |
| |
| else |
| { |
| /* Notice if this instruction uses the flags register. */ |
| if (last_cmp) |
| find_flags_uses_in_insn (last_cmp, insn); |
| |
| /* Notice if this instruction kills the flags register. */ |
| df_ref def; |
| FOR_EACH_INSN_DEF (def, insn) |
| if (DF_REF_REGNO (def) == 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; |
| break; |
| } |
| } |
| |
| /* Notice if any of the inputs to the comparison have changed |
| and remember last insn that sets each register. */ |
| df_ref def; |
| FOR_EACH_INSN_DEF (def, insn) |
| { |
| if (last_cmp_valid |
| && (DF_REF_REGNO (def) == REGNO (last_cmp->in_a) |
| || (REG_P (last_cmp->in_b) |
| && DF_REF_REGNO (def) == REGNO (last_cmp->in_b)))) |
| last_cmp_valid = false; |
| last_setter[DF_REF_REGNO (def)] = insn; |
| } |
| } |
| |
| /* 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; |
| } |
| } |
| } |
| } |
| |
| /* If we deleted a compare with a REG_EH_REGION note, we may need to |
| remove EH edges. */ |
| if (need_purge) |
| purge_dead_edges (bb); |
| |
| return NULL; |
| } |
| |
| /* 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) |
| { |
| 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) |
| { |
| machine_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; |
| } |
| |
| /* Return a register RTX holding the same value at START as REG at END, or |
| NULL_RTX if there is none. */ |
| |
| static rtx |
| equivalent_reg_at_start (rtx reg, rtx_insn *end, rtx_insn *start) |
| { |
| machine_mode orig_mode = GET_MODE (reg); |
| rtx_insn *bb_head = BB_HEAD (BLOCK_FOR_INSN (end)); |
| |
| for (rtx_insn *insn = PREV_INSN (end); |
| insn != start; |
| 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; |
| |
| /* Note that the BB_HEAD is always either a note or a label, but in |
| any case it means that REG is defined outside the block. */ |
| if (insn == bb_head) |
| return NULL_RTX; |
| if (NOTE_P (insn) || DEBUG_INSN_P (insn)) |
| continue; |
| |
| /* Find a possible def of REG in INSN. */ |
| FOR_EACH_INSN_DEF (def, insn) |
| if (DF_REF_REGNO (def) == REGNO (reg)) |
| break; |
| |
| /* No definitions of REG; continue searching. */ |
| if (def == NULL) |
| continue; |
| |
| /* Bail if this is not a totally normal set of REG. */ |
| if (DF_REF_IS_ARTIFICIAL (def)) |
| return NULL_RTX; |
| if (DF_REF_FLAGS (def) & abnormal_flags) |
| return NULL_RTX; |
| |
| /* We've found an insn between the compare and the clobber that sets |
| REG. Given that pass_cprop_hardreg has not yet run, we still find |
| situations in which we can usefully look through a copy insn. */ |
| rtx x = single_set (insn); |
| if (x == NULL_RTX) |
| return NULL_RTX; |
| reg = SET_SRC (x); |
| if (!REG_P (reg)) |
| return NULL_RTX; |
| } |
| |
| if (GET_MODE (reg) != orig_mode) |
| return NULL_RTX; |
| |
| return reg; |
| } |
| |
| /* Return true if it is okay to merge the comparison CMP_INSN with |
| the instruction ARITH_INSN. Both instructions are assumed to be in the |
| same basic block with ARITH_INSN appearing before CMP_INSN. This checks |
| that there are no uses or defs of the condition flags or control flow |
| changes between the two instructions. */ |
| |
| static bool |
| can_merge_compare_into_arith (rtx_insn *cmp_insn, rtx_insn *arith_insn) |
| { |
| for (rtx_insn *insn = PREV_INSN (cmp_insn); |
| insn && insn != arith_insn; |
| insn = PREV_INSN (insn)) |
| { |
| if (!NONDEBUG_INSN_P (insn)) |
| continue; |
| /* Bail if there are jumps or calls in between. */ |
| if (!NONJUMP_INSN_P (insn)) |
| return false; |
| |
| /* Bail on old-style asm statements because they lack |
| data flow information. */ |
| if (GET_CODE (PATTERN (insn)) == ASM_INPUT) |
| return false; |
| |
| df_ref ref; |
| /* Find a USE of the flags register. */ |
| FOR_EACH_INSN_USE (ref, insn) |
| if (DF_REF_REGNO (ref) == targetm.flags_regnum) |
| return false; |
| |
| /* Find a DEF of the flags register. */ |
| FOR_EACH_INSN_DEF (ref, insn) |
| if (DF_REF_REGNO (ref) == targetm.flags_regnum) |
| return false; |
| } |
| return true; |
| } |
| |
| /* Given two SET expressions, SET_A and SET_B determine whether they form |
| a recognizable pattern when emitted in parallel. Return that parallel |
| if so. Otherwise return NULL. */ |
| |
| static rtx |
| try_validate_parallel (rtx set_a, rtx set_b) |
| { |
| rtx par = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, set_a, set_b)); |
| rtx_insn *insn = make_insn_raw (par); |
| |
| if (insn_invalid_p (insn, false)) |
| { |
| crtl->emit.x_cur_insn_uid--; |
| return NULL_RTX; |
| } |
| |
| SET_PREV_INSN (insn) = NULL_RTX; |
| SET_NEXT_INSN (insn) = NULL_RTX; |
| INSN_LOCATION (insn) = 0; |
| return insn; |
| } |
| |
| /* For a comparison instruction described by CMP check if it compares a |
| register with zero i.e. it is of the form CC := CMP R1, 0. |
| If it is, find the instruction defining R1 (say I1) and try to create a |
| PARALLEL consisting of I1 and the comparison, representing a flag-setting |
| arithmetic instruction. Example: |
| I1: R1 := R2 + R3 |
| <instructions that don't read the condition register> |
| I2: CC := CMP R1 0 |
| I2 can be merged with I1 into: |
| I1: { CC := CMP (R2 + R3) 0 ; R1 := R2 + R3 } |
| This catches cases where R1 is used between I1 and I2 and therefore |
| combine and other RTL optimisations will not try to propagate it into |
| I2. Return true if we succeeded in merging CMP. */ |
| |
| static bool |
| try_merge_compare (struct comparison *cmp) |
| { |
| rtx_insn *cmp_insn = cmp->insn; |
| |
| if (cmp->in_b != const0_rtx || cmp->in_a_setter == NULL) |
| return false; |
| rtx in_a = cmp->in_a; |
| df_ref use; |
| |
| FOR_EACH_INSN_USE (use, cmp_insn) |
| if (DF_REF_REGNO (use) == REGNO (in_a)) |
| break; |
| if (!use) |
| return false; |
| |
| rtx_insn *def_insn = cmp->in_a_setter; |
| rtx set = single_set (def_insn); |
| if (!set) |
| return false; |
| |
| if (!can_merge_compare_into_arith (cmp_insn, def_insn)) |
| return false; |
| |
| rtx src = SET_SRC (set); |
| |
| /* If the source uses addressing modes with side effects, we can't |
| do the merge because we'd end up with a PARALLEL that has two |
| instances of that side effect in it. */ |
| if (side_effects_p (src)) |
| return false; |
| |
| rtx flags = maybe_select_cc_mode (cmp, src, CONST0_RTX (GET_MODE (src))); |
| if (!flags) |
| { |
| /* We may already have a change group going through maybe_select_cc_mode. |
| Discard it properly. */ |
| cancel_changes (0); |
| return false; |
| } |
| |
| rtx flag_set |
| = gen_rtx_SET (flags, gen_rtx_COMPARE (GET_MODE (flags), |
| copy_rtx (src), |
| CONST0_RTX (GET_MODE (src)))); |
| rtx arith_set = copy_rtx (PATTERN (def_insn)); |
| rtx par = try_validate_parallel (flag_set, arith_set); |
| if (!par) |
| { |
| /* We may already have a change group going through maybe_select_cc_mode. |
| Discard it properly. */ |
| cancel_changes (0); |
| return false; |
| } |
| if (!apply_change_group ()) |
| return false; |
| emit_insn_after (par, def_insn); |
| delete_insn (def_insn); |
| delete_insn (cmp->insn); |
| return true; |
| } |
| |
| /* 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 flags, in_a, in_b, cmp_a, cmp_b; |
| |
| if (try_merge_compare (cmp)) |
| return true; |
| |
| /* We must have found an interesting "clobber" preceding the compare. */ |
| if (cmp->prev_clobber == NULL) |
| 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 = equivalent_reg_at_start (cmp->in_a, cmp->insn, cmp->prev_clobber); |
| if (!in_a) |
| return false; |
| |
| /* Likewise for IN_B if need be. */ |
| if (CONSTANT_P (cmp->in_b)) |
| in_b = cmp->in_b; |
| else if (REG_P (cmp->in_b)) |
| { |
| in_b = equivalent_reg_at_start (cmp->in_b, cmp->insn, cmp->prev_clobber); |
| if (!in_b) |
| return false; |
| } |
| else if (GET_CODE (cmp->in_b) == UNSPEC) |
| { |
| const int len = XVECLEN (cmp->in_b, 0); |
| rtvec v = rtvec_alloc (len); |
| for (int i = 0; i < len; i++) |
| { |
| rtx r = equivalent_reg_at_start (XVECEXP (cmp->in_b, 0, i), |
| cmp->insn, cmp->prev_clobber); |
| if (!r) |
| return false; |
| RTVEC_ELT (v, i) = r; |
| } |
| in_b = gen_rtx_UNSPEC (GET_MODE (cmp->in_b), v, XINT (cmp->in_b, 1)); |
| } |
| else |
| gcc_unreachable (); |
| |
| /* 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. */ |
| rtx_insn *insn = cmp->prev_clobber; |
| |
| rtx x = XVECEXP (PATTERN (insn), 0, 0); |
| if (rtx_equal_p (SET_DEST (x), in_a)) |
| cmp_a = 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_a = XEXP (SET_SRC (x), 0); |
| |
| /* Also check fully redundant comparisons, e.g.: |
| [(set (reg:SI) |
| (minus:SI (reg:SI) (reg:SI)))) |
| (set (reg:CC flags) |
| (compare:CC (reg:SI) (reg:SI)))] */ |
| else if (REG_P (in_b) |
| && GET_CODE (SET_SRC (x)) == MINUS |
| && rtx_equal_p (XEXP (SET_SRC (x), 0), in_a) |
| && rtx_equal_p (XEXP (SET_SRC (x), 1), in_b)) |
| cmp_a = in_a; |
| |
| else |
| return false; |
| |
| /* If the source uses addressing modes with side effects, we can't |
| do the merge because we'd end up with a PARALLEL that has two |
| instances of that side effect in it. */ |
| if (side_effects_p (cmp_a)) |
| return false; |
| |
| if (in_a == in_b) |
| cmp_b = cmp_a; |
| else if (rtx_equal_p (SET_DEST (x), in_b)) |
| cmp_b = SET_SRC (x); |
| else |
| cmp_b = in_b; |
| if (side_effects_p (cmp_b)) |
| return false; |
| |
| /* Determine if we ought to use a different CC_MODE here. */ |
| flags = maybe_select_cc_mode (cmp, cmp_a, cmp_b); |
| if (flags == NULL) |
| flags = gen_rtx_REG (cmp->orig_mode, targetm.flags_regnum); |
| |
| /* Generate a new comparison for installation in the setter. */ |
| rtx y = cmp->not_in_a |
| ? gen_rtx_NOT (GET_MODE (cmp_a), copy_rtx (cmp_a)) |
| : copy_rtx (cmp_a); |
| y = gen_rtx_COMPARE (GET_MODE (flags), y, copy_rtx (cmp_b)); |
| y = gen_rtx_SET (flags, y); |
| |
| /* Canonicalize instruction to: |
| [(set (reg:CCM) (compare:CCM (operation) (immediate))) |
| (set (reg) (operation)] */ |
| |
| rtvec v = rtvec_alloc (2); |
| RTVEC_ELT (v, 0) = y; |
| RTVEC_ELT (v, 1) = x; |
| |
| rtx pat = gen_rtx_PARALLEL (VOIDmode, v); |
| |
| /* 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, &PATTERN (insn), pat, 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; |
| } |
| |
| namespace { |
| |
| const pass_data pass_data_compare_elim_after_reload = |
| { |
| RTL_PASS, /* type */ |
| "cmpelim", /* name */ |
| OPTGROUP_NONE, /* optinfo_flags */ |
| TV_NONE, /* tv_id */ |
| 0, /* properties_required */ |
| 0, /* properties_provided */ |
| 0, /* properties_destroyed */ |
| 0, /* todo_flags_start */ |
| ( TODO_df_finish | TODO_df_verify ), /* 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: */ |
| virtual bool gate (function *) |
| { |
| /* 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; |
| } |
| |
| virtual unsigned int execute (function *) |
| { |
| 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); |
| } |