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From 79d1ed2d7f166a498662f6111a4defc55f0061c7 Mon Sep 17 00:00:00 2001
From: yangyang <yangyang305@huawei.com>
Date: Thu, 15 Jul 2021 09:27:27 +0800
Subject: [PATCH 08/13] [Backport]tree-optimization: Add checks to avoid
spoiling if-conversion
Reference: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=33d114f570b4a3583421c700396fd5945acebc28
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.
diff --git a/gcc/gimple-ssa-split-paths.c b/gcc/gimple-ssa-split-paths.c
index b3efd43c7ef..9c32da76369 100644
--- a/gcc/gimple-ssa-split-paths.c
+++ b/gcc/gimple-ssa-split-paths.c
@@ -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;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/split-path-12.c b/gcc/testsuite/gcc.dg/tree-ssa/split-path-12.c
new file mode 100644
index 00000000000..19a130d9bf1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/split-path-12.c
@@ -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" } } */
--
2.21.0.windows.1
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