From: Richard Biener <rguenther@suse.de>
To: gcc-patches@gcc.gnu.org
Subject: [PATCH] tree-optimization/100112 - VN last_vuse and redundant store elimination
Date: Mon, 27 Sep 2021 15:07:55 +0200 (CEST) [thread overview]
Message-ID: <ssr9r895-9599-1n6-o53o-1q1r82po32p@fhfr.qr> (raw)
This avoids the last_vuse optimization hindering redundant store
elimination by always also recording the original VUSE that was
in effect on the load.
Bootstrapped and tested on x86_64-unknown-linux-gnu.
I'm still pondering on how to avoid the wastage of adding the ref
twice and will at least record some statistics for this.
2021-09-27 Richard Biener <rguenther@suse.de>
PR tree-optimization/100112
* tree-ssa-sccvn.c (visit_reference_op_load): Record the
referece into the hashtable twice in case last_vuse is
different from the original vuse on the stmt.
* gcc.dg/tree-ssa/ssa-fre-95.c: New testcase.
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c | 25 ++++++++++++++++++++++
gcc/tree-ssa-sccvn.c | 17 +++++++++++----
2 files changed, 38 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c
new file mode 100644
index 00000000000..b0936be5e77
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-95.c
@@ -0,0 +1,25 @@
+/* PR100112 and dups. */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fre1-details -fdump-tree-optimized" } */
+
+int *c, *b;
+void foo()
+{
+ int *tem = b;
+ *tem = 0;
+ int *footem = c;
+ c = footem;
+}
+
+void bar()
+{
+ int *tem = b;
+ int *bartem = c;
+ *tem = 0;
+ c = bartem;
+}
+
+/* We should elide the redundant store in foo, in bar it is not redundant since
+ the *tem = 0 store might alias. */
+/* { dg-final { scan-tree-dump "Deleted redundant store c = footem" "fre1" } } */
+/* { dg-final { scan-tree-dump "c = bartem" "optimized" } } */
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index e8b1c39184d..416a5252144 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -5125,13 +5125,12 @@ static bool
visit_reference_op_load (tree lhs, tree op, gimple *stmt)
{
bool changed = false;
- tree last_vuse;
tree result;
vn_reference_t res;
- last_vuse = gimple_vuse (stmt);
- result = vn_reference_lookup (op, gimple_vuse (stmt),
- default_vn_walk_kind, &res, true, &last_vuse);
+ tree vuse = gimple_vuse (stmt);
+ tree last_vuse = vuse;
+ result = vn_reference_lookup (op, vuse, default_vn_walk_kind, &res, true, &last_vuse);
/* We handle type-punning through unions by value-numbering based
on offset and size of the access. Be prepared to handle a
@@ -5174,6 +5173,16 @@ visit_reference_op_load (tree lhs, tree op, gimple *stmt)
{
changed = set_ssa_val_to (lhs, lhs);
vn_reference_insert (op, lhs, last_vuse, NULL_TREE);
+ if (vuse && SSA_VAL (last_vuse) != SSA_VAL (vuse))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Using extra use virtual operand ");
+ print_generic_expr (dump_file, last_vuse);
+ fprintf (dump_file, "\n");
+ }
+ vn_reference_insert (op, lhs, vuse, NULL_TREE);
+ }
}
return changed;
--
2.31.1
next reply other threads:[~2021-09-27 13:07 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-27 13:07 Richard Biener [this message]
2021-09-27 14:11 ` Richard Biener
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