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New -fcompare-elim pass.

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Version 3, with two rounds of comments from Paolo Bonzini.

From-SVN: r169131
This commit is contained in:
Richard Henderson 2011-01-22 11:35:10 -08:00 committed by Richard Henderson
parent 8a9adf2c8f
commit e692f27683
12 changed files with 701 additions and 1 deletions
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15
gcc/ChangeLog
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@ -1,3 +1,18 @@
2011-01-21 Richard Henderson <rth@redhat.com>
* compare-elim.c: New file.
* Makefile.in (OBJS-common): Add it.
(compare-elim.o): New.
* common.opt (fcompare-elim): New.
* opts.c (default_options_table): Add OPT_fcompare_elim.
* tree-pass.h (pass_compare_elim_after_reload): New.
* passes.c (init_optimization_passes): Add it.
* recog.h: Protect against re-inclusion.
* target.def (TARGET_FLAGS_REGNUM): New POD hook.
* doc/invoke.texi (-fcompare-elim): Document it.
* doc/tm.texi.in (TARGET_FLAGS_REGNUM): Document it.
* doc/tm.texi: Rebuild.
2011-01-22 Nick Clifton <nickc@redhat.com>
* config/rx/rx.md (cstoresf4): Pass comparison operator to

4
gcc/Makefile.in
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@ -1205,6 +1205,7 @@ OBJS-common = \
cfgrtl.o \
combine.o \
combine-stack-adj.o \
compare-elim.o \
convert.o \
coverage.o \
cse.o \
@ -3353,6 +3354,9 @@ combine-stack-adj.o : combine-stack-adj.c $(CONFIG_H) $(SYSTEM_H) coretypes.h \
$(TM_H) $(RTL_H) insn-config.h $(TIMEVAR_H) $(TREE_PASS_H) \
$(RECOG_H) output.h $(REGS_H) hard-reg-set.h $(FLAGS_H) $(FUNCTION_H) \
$(EXPR_H) $(BASIC_BLOCK_H) $(DIAGNOSTIC_CORE_H) $(TM_P_H) $(DF_H) $(EXCEPT_H) reload.h
compare-elim.o : compare-elim.c $(CONFIG_H) $(SYSTEM_H) coretypes.h \
$(TM_H) $(RTL_H) $(TM_P_H) insn-config.h $(RECOG_H) $(FLAGS_H) \
$(BASIC_BLOCK_H) $(TREE_PASS_H) $(TARGET_H) $(DF_H) domwalk.h
ddg.o : ddg.c $(DDG_H) $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TARGET_H) \
$(DIAGNOSTIC_CORE_H) $(RTL_H) $(TM_P_H) $(REGS_H) $(FUNCTION_H) \
$(FLAGS_H) insn-config.h $(INSN_ATTR_H) $(EXCEPT_H) $(RECOG_H) \

4
gcc/common.opt
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@ -853,6 +853,10 @@ fcompare-debug-second
Common Driver RejectNegative Var(flag_compare_debug)
Run only the second compilation of -fcompare-debug
fcompare-elim
Common Report Var(flag_compare_elim_after_reload) Optimization
Perform comparison elimination after register allocation has finished
fconserve-stack
Common Var(flag_conserve_stack) Optimization
Do not perform optimizations increasing noticeably stack usage

641
gcc/compare-elim.c Normal file
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@ -0,0 +1,641 @@
/* 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"
/* 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, rtx b)
{
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 */
}
};

15
gcc/doc/invoke.texi
View File

@ -337,7 +337,7 @@ Objective-C and Objective-C++ Dialects}.
-fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
-fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
-fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol
-fcprop-registers -fcrossjumping @gol
-fcompare-elim -fcprop-registers -fcrossjumping @gol
-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
-fcx-limited-range @gol
-fdata-sections -fdce -fdce -fdelayed-branch @gol
@ -5870,6 +5870,7 @@ compilation time.
@option{-O} turns on the following optimization flags:
@gccoptlist{
-fauto-inc-dec @gol
-fcompare-elim @gol
-fcprop-registers @gol
-fdce @gol
-fdefer-pop @gol
@ -7689,6 +7690,18 @@ use hidden visibility) is similar to @code{-fwhole-program}. See
Enabled by default when LTO support in GCC is enabled and GCC was compiled
with linker supporting plugins (GNU ld or @code{gold}).
@item -fcompare-elim
@opindex fcompare-elim
After register allocation and post-register allocation instruction splitting,
identify arithmetic instructions that compute processor flags similar to a
comparison operation based on that arithmetic. If possible, eliminate the
explicit comparison operation.
This pass only applies to certain targets that cannot explicitly represent
the comparison operation before register allocation is complete.
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
@item -fcprop-registers
@opindex fcprop-registers
After register allocation and post-register allocation instruction splitting,

4
gcc/doc/tm.texi
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@ -4351,6 +4351,10 @@ to return a nonzero value when it is required, the compiler will run out
of spill registers and print a fatal error message.
@end deftypefn
@deftypevr {Target Hook} {unsigned int} TARGET_FLAGS_REGNUM
If the target has a dedicated flags register, and it needs to use the post-reload comparison elimination pass, then this value should be set appropriately.
@end deftypevr
@node Scalar Return
@subsection How Scalar Function Values Are Returned
@cindex return values in registers

2
gcc/doc/tm.texi.in
View File

@ -4337,6 +4337,8 @@ to return a nonzero value when it is required, the compiler will run out
of spill registers and print a fatal error message.
@end deftypefn
@hook TARGET_FLAGS_REGNUM
@node Scalar Return
@subsection How Scalar Function Values Are Returned
@cindex return values in registers

1
gcc/opts.c
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@ -456,6 +456,7 @@ static const struct default_options default_options_table[] =
{ OPT_LEVELS_1_PLUS, OPT_ftree_sink, NULL, 1 },
{ OPT_LEVELS_1_PLUS, OPT_ftree_ch, NULL, 1 },
{ OPT_LEVELS_1_PLUS, OPT_fcombine_stack_adjustments, NULL, 1 },
{ OPT_LEVELS_1_PLUS, OPT_fcompare_elim, NULL, 1 },
/* -O2 optimizations. */
{ OPT_LEVELS_2_PLUS, OPT_finline_small_functions, NULL, 1 },

1
gcc/passes.c
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@ -1022,6 +1022,7 @@ init_optimization_passes (void)
NEXT_PASS (pass_gcse2);
NEXT_PASS (pass_split_after_reload);
NEXT_PASS (pass_implicit_zee);
NEXT_PASS (pass_compare_elim_after_reload);
NEXT_PASS (pass_branch_target_load_optimize1);
NEXT_PASS (pass_thread_prologue_and_epilogue);
NEXT_PASS (pass_rtl_dse2);

5
gcc/recog.h
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@ -18,6 +18,9 @@ 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/>. */
#ifndef GCC_RECOG_H
#define GCC_RECOG_H
/* Random number that should be large enough for all purposes. */
#define MAX_RECOG_ALTERNATIVES 30
@ -305,3 +308,5 @@ struct insn_data_d
extern const struct insn_data_d insn_data[];
extern int peep2_current_count;
#endif /* GCC_RECOG_H */

9
gcc/target.def
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@ -1638,6 +1638,15 @@ DEFHOOK
bool, (enum machine_mode mode),
hook_bool_mode_false)
/* Register number for a flags register. Only needs to be defined if the
target is constrainted to use post-reload comparison elimination. */
DEFHOOKPOD
(flags_regnum,
"If the target has a dedicated flags register, and it needs to use the\
post-reload comparison elimination pass, then this value should be set\
appropriately.",
unsigned int, INVALID_REGNUM)
/* Compute a (partial) cost for rtx X. Return true if the complete
cost has been computed, and false if subexpressions should be
scanned. In either case, *TOTAL contains the cost result. */

1
gcc/tree-pass.h
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@ -551,6 +551,7 @@ extern struct rtl_opt_pass pass_reorder_blocks;
extern struct rtl_opt_pass pass_branch_target_load_optimize2;
extern struct rtl_opt_pass pass_leaf_regs;
extern struct rtl_opt_pass pass_split_before_sched2;
extern struct rtl_opt_pass pass_compare_elim_after_reload;
extern struct rtl_opt_pass pass_sched2;
extern struct rtl_opt_pass pass_stack_regs;
extern struct rtl_opt_pass pass_stack_regs_run;