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tree-optimization/95855 - Add checks to avoid spoiling if-conversion if

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Add some checks in pass_splits_paths, so that pass_split_paths can
recognize the missed if-conversion opportunity and do not duplicate the
corresponding block.

2020-06-30 Yang Yang <yangyang305@huawei.com>

gcc/ChangeLog:

	PR tree-optimization/95855
	* gimple-ssa-split-paths.c (is_feasible_trace): Add extra
	checks to recognize a missed if-conversion opportunity when
	judging whether to duplicate a block.

gcc/testsuite/ChangeLog

	PR tree-optimization/95855
	* gcc.dg/tree-ssa/split-path-12.c: New testcase.
This commit is contained in:
Yang Yang 2020-06-30 18:04:31 +08:00 committed by Richard Biener
parent 7d503e3299
commit 33d114f570
2 changed files with 58 additions and 0 deletions
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39
gcc/gimple-ssa-split-paths.c
View File

@ -34,6 +34,7 @@ along with GCC; see the file COPYING3. If not see
#include "gimple-ssa.h"
#include "tree-phinodes.h"
#include "ssa-iterators.h"
#include "fold-const.h"
/* Given LATCH, the latch block in a loop, see if the shape of the
path reaching LATCH is suitable for being split by duplication.
@ -254,6 +255,44 @@ is_feasible_trace (basic_block bb)
}
}
/* Canonicalize the form. */
if (single_pred_p (pred1) && single_pred (pred1) == pred2
&& num_stmts_in_pred1 == 0)
std::swap (pred1, pred2);
/* This is meant to catch another kind of cases that are likely opportunities
for if-conversion. After canonicalizing, PRED2 must be an empty block and
PRED1 must be the only predecessor of PRED2. Moreover, PRED1 is supposed
to end with a cond_stmt which has the same args with the PHI in BB. */
if (single_pred_p (pred2) && single_pred (pred2) == pred1
&& num_stmts_in_pred2 == 0)
{
gimple *cond_stmt = last_stmt (pred1);
if (cond_stmt && gimple_code (cond_stmt) == GIMPLE_COND)
{
tree lhs = gimple_cond_lhs (cond_stmt);
tree rhs = gimple_cond_rhs (cond_stmt);
gimple_stmt_iterator gsi;
for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple *phi = gsi_stmt (gsi);
if ((operand_equal_p (gimple_phi_arg_def (phi, 0), lhs)
&& operand_equal_p (gimple_phi_arg_def (phi, 1), rhs))
|| (operand_equal_p (gimple_phi_arg_def (phi, 0), rhs)
&& (operand_equal_p (gimple_phi_arg_def (phi, 1), lhs))))
{
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file,
"Block %d appears to be optimized to a join "
"point for if-convertable half-diamond.\n",
bb->index);
return false;
}
}
}
}
/* If the joiner has no PHIs with useful uses there is zero chance
of CSE/DCE/jump-threading possibilities exposed by duplicating it. */
bool found_useful_phi = false;

19
gcc/testsuite/gcc.dg/tree-ssa/split-path-12.c Normal file
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@ -0,0 +1,19 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fsplit-paths -fdump-tree-split-paths-details " } */
double
foo(double *d1, double *d2, double *d3, int num, double *ip)
{
double dmax[3];
for (int i = 0; i < num; i++) {
dmax[0] = d1[i] < dmax[0] ? dmax[0] : d1[i];
dmax[1] = d2[i] < dmax[1] ? dmax[1] : d2[i];
dmax[2] = d3[i] < dmax[2] ? dmax[2] : d3[i];
ip[i] = dmax[2];
}
return dmax[0] + dmax[1] + dmax[2];
}
/* { dg-final { scan-tree-dump "appears to be optimized to a join point for if-convertable half-diamond" "split-paths" } } */