+++ /dev/null
-/* Post-reload compare elimination.
- Copyright (C) 2010, 2011
- 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"
-
-\f
-/* 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;
-DEF_VEC_P(comparison_struct_p);
-DEF_VEC_ALLOC_P(comparison_struct_p, heap);
-
-static VEC(comparison_struct_p, heap) *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;
-}
-
-/* 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 walk_dominators_tree. */
-
-static void
-find_comparisons_in_bb (struct dom_walk_data *data ATTRIBUTE_UNUSED,
- 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)
- {
- /* 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)))
- {
- 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 = GET_MODE (SET_DEST (single_set (insn)));
- VEC_safe_push (comparison_struct_p, heap, all_compares, 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_LIVE_BB_INFO (bb)->out, 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_LIVE_BB_INFO (dest)->in,
- targetm.flags_regnum)
- && !single_pred_p (dest))
- {
- last_cmp->missing_uses = true;
- break;
- }
- }
- }
- }
-}
-
-/* Find all comparisons in the function. */
-
-static void
-find_comparisons (void)
-{
- struct dom_walk_data data;
-
- memset (&data, 0, sizeof(data));
- data.dom_direction = CDI_DOMINATORS;
- data.before_dom_children = find_comparisons_in_bb;
-
- calculate_dominance_info (CDI_DOMINATORS);
-
- init_walk_dominator_tree (&data);
- walk_dominator_tree (&data, ENTRY_BLOCK_PTR);
- fini_walk_dominator_tree (&data);
-
- 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" preceeding 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))
- return false;
- cmp_src = SET_SRC (x);
-
- /* 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_set_flags (DF_DEFER_INSN_RESCAN);
- df_live_add_problem ();
- df_analyze ();
-
- gcc_checking_assert (all_compares == NULL);
-
- /* Locate all comparisons and their uses, and eliminate duplicates. */
- find_comparisons ();
- if (all_compares)
- {
- struct comparison *cmp;
- size_t i;
-
- /* Eliminate comparisons that are redundant with flags computation. */
- FOR_EACH_VEC_ELT (comparison_struct_p, all_compares, i, cmp)
- {
- try_eliminate_compare (cmp);
- XDELETE (cmp);
- }
-
- VEC_free (comparison_struct_p, heap, all_compares);
- all_compares = NULL;
-
- df_analyze ();
- }
-
- 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;
-}
-
-struct rtl_opt_pass pass_compare_elim_after_reload =
-{
- {
- RTL_PASS,
- "cmpelim", /* name */
- gate_compare_elim_after_reload, /* gate */
- execute_compare_elim_after_reload, /* execute */
- NULL, /* sub */
- NULL, /* next */
- 0, /* static_pass_number */
- 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_dump_func
- | TODO_ggc_collect /* todo_flags_finish */
- }
-};
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