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Remove global call sets: early-remat.c 

This pass previously excluded rematerialisation candidates if they
clobbered a call-preserved register, on the basis that it then
wouldn't be safe to add new instances of the candidate instruction
after a call.  This patch instead makes the decision on a call-by-call
basis.

The second emit_remat_insns_for_block hunk probably isn't needed,
but it seems safer and more consistent to have it, so that every call
to emit_remat_insns is preceded by a check for invalid clobbers.

2019-09-30  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* early-remat.c: Include regs.h and function-abi.h.
	(early_remat::maybe_add_candidate): Don't check for call-clobbered
	registers here.
	(early_remat::restrict_remat_for_unavail_regs): New function.
	(early_remat::restrict_remat_for_call): Likewise.
	(early_remat::process_block): Before calling emit_remat_insns
	for a previous call in the block, invalidate any candidates
	that would clobber call-preserved registers.
	(early_remat::emit_remat_insns_for_block): Likewise for the
	final call in a block.  Do the same thing for live-in registers
	when calling emit_remat_insns at the head of a block.

From-SVN: r276321
This commit is contained in:
Richard Sandiford 2019-09-30 16:20:37 +00:00 committed by Richard Sandiford
parent 559c1ae100
commit 1849569621
2 changed files with 66 additions and 22 deletions
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14
gcc/ChangeLog
View File

@ -1,3 +1,17 @@
2019-09-30 Richard Sandiford <richard.sandiford@arm.com>
* early-remat.c: Include regs.h and function-abi.h.
(early_remat::maybe_add_candidate): Don't check for call-clobbered
registers here.
(early_remat::restrict_remat_for_unavail_regs): New function.
(early_remat::restrict_remat_for_call): Likewise.
(early_remat::process_block): Before calling emit_remat_insns
for a previous call in the block, invalidate any candidates
that would clobber call-preserved registers.
(early_remat::emit_remat_insns_for_block): Likewise for the
final call in a block. Do the same thing for live-in registers
when calling emit_remat_insns at the head of a block.
2019-09-30 Richard Sandiford <richard.sandiford@arm.com>
* df-scan.c (df_get_entry_block_def_set): Use crtl->abi to test

74
gcc/early-remat.c
View File

@ -36,6 +36,8 @@ along with GCC; see the file COPYING3. If not see
#include "rtlhash.h"
#include "print-rtl.h"
#include "rtl-iter.h"
#include "regs.h"
#include "function-abi.h"
/* This pass runs before register allocation and implements an aggressive
form of rematerialization. It looks for pseudo registers R of mode M
@ -435,6 +437,8 @@ private:
void compute_clobbers (unsigned int);
void assign_value_number (unsigned int);
void decide_candidate_validity (void);
void restrict_remat_for_unavail_regs (bitmap, const_bitmap);
void restrict_remat_for_call (bitmap, rtx_insn *);
bool stable_use_p (unsigned int);
void emit_copy_before (unsigned int, rtx, rtx);
void stabilize_pattern (unsigned int);
@ -889,8 +893,8 @@ early_remat::maybe_add_candidate (rtx_insn *insn, unsigned int regno)
else
{
/* The instruction can set additional registers, provided that
they're call-clobbered hard registers. This is useful for
instructions that alter the condition codes. */
they're hard registers. This is useful for instructions
that alter the condition codes. */
if (!HARD_REGISTER_NUM_P (def_regno))
{
if (dump_file)
@ -898,20 +902,6 @@ early_remat::maybe_add_candidate (rtx_insn *insn, unsigned int regno)
" pseudo reg %d\n", FAILURE_ARGS, def_regno);
return false;
}
if (global_regs[def_regno])
{
if (dump_file)
fprintf (dump_file, FAILURE_FORMAT "insn also sets"
" global reg %d\n", FAILURE_ARGS, def_regno);
return false;
}
if (!TEST_HARD_REG_BIT (regs_invalidated_by_call, def_regno))
{
if (dump_file)
fprintf (dump_file, FAILURE_FORMAT "insn also sets"
" call-preserved reg %d\n", FAILURE_ARGS, def_regno);
return false;
}
}
}
@ -1532,6 +1522,39 @@ early_remat::decide_candidate_validity (void)
}
}
/* Remove any candidates in CANDIDATES that would clobber a register in
UNAVAIL_REGS. */
void
early_remat::restrict_remat_for_unavail_regs (bitmap candidates,
const_bitmap unavail_regs)
{
bitmap_clear (&m_tmp_bitmap);
unsigned int cand_index;
bitmap_iterator bi;
EXECUTE_IF_SET_IN_BITMAP (candidates, 0, cand_index, bi)
{
remat_candidate *cand = &m_candidates[cand_index];
if (cand->clobbers
&& bitmap_intersect_p (cand->clobbers, unavail_regs))
bitmap_set_bit (&m_tmp_bitmap, cand_index);
}
bitmap_and_compl_into (candidates, &m_tmp_bitmap);
}
/* Remove any candidates in CANDIDATES that would clobber a register
that is potentially live across CALL. */
void
early_remat::restrict_remat_for_call (bitmap candidates, rtx_insn *call)
{
/* We don't know whether partially-clobbered registers are live
across the call or not, so assume that they are. */
bitmap_view<HARD_REG_SET> call_preserved_regs
(~insn_callee_abi (call).full_reg_clobbers ());
restrict_remat_for_unavail_regs (candidates, call_preserved_regs);
}
/* Assuming that every path reaching a point P contains a copy of a
use U of REGNO, return true if another copy of U at P would have
access to the same value of REGNO. */
@ -1984,10 +2007,13 @@ early_remat::process_block (basic_block bb)
init_temp_bitmap (&m_required);
}
else
/* The fully-local case: candidates that need to be
rematerialized after a previous call in the block. */
emit_remat_insns (m_required, NULL, info->rd_after_call,
last_call);
{
/* The fully-local case: candidates that need to be
rematerialized after a previous call in the block. */
restrict_remat_for_call (m_required, last_call);
emit_remat_insns (m_required, NULL, info->rd_after_call,
last_call);
}
last_call = insn;
bitmap_clear (m_available);
gcc_checking_assert (empty_p (m_required));
@ -2480,8 +2506,11 @@ early_remat::emit_remat_insns_for_block (basic_block bb)
remat_block_info *info = &m_block_info[bb->index];
if (info->last_call && !empty_p (info->required_after_call))
emit_remat_insns (info->required_after_call, NULL,
info->rd_after_call, info->last_call);
{
restrict_remat_for_call (info->required_after_call, info->last_call);
emit_remat_insns (info->required_after_call, NULL,
info->rd_after_call, info->last_call);
}
if (!empty_p (info->required_in))
{
@ -2489,6 +2518,7 @@ early_remat::emit_remat_insns_for_block (basic_block bb)
while (insn != BB_END (bb)
&& !INSN_P (NEXT_INSN (insn)))
insn = NEXT_INSN (insn);
restrict_remat_for_unavail_regs (info->required_in, DF_LR_IN (bb));
emit_remat_insns (info->required_in, info->available_in,
info->rd_in, insn);
}