https://gcc.gnu.org/g:7b4849ec79873fa6de98436deda47e19cbac32ef
commit r16-23-g7b4849ec79873fa6de98436deda47e19cbac32ef
Author: Andrew Pinski <quic_apin...@quicinc.com>
Date: Mon Feb 24 12:33:32 2025 -0800
gimple-fold: Improve optimize_memcpy_to_memset by walking back until
aliasing says the ref is a may clobber. [PR118947]
The case here is we have:
```
char buf[32] = {};
void* ret = aaa();
__builtin_memcpy(ret, buf, 32);
```
And buf does not escape. But we don't prop the zeroing from buf to the
memcpy statement
because optimize_memcpy_to_memset only looks back one statement. This can
be fixed to look back
until we get an statement that may clobber the reference. If we get a phi
node, then we don't do
anything.
Bootstrapped and tested on x86_64-linux-gnu.
PR tree-optimization/118947
gcc/ChangeLog:
* gimple-fold.cc (optimize_memcpy_to_memset): Walk back until we
get a
statement that may clobber the read.
gcc/testsuite/ChangeLog:
* gcc.dg/pr118947-1.c: New test.
Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
Diff:
---
gcc/gimple-fold.cc | 39 ++++++++++++++++++++++++++++-----------
gcc/testsuite/gcc.dg/pr118947-1.c | 15 +++++++++++++++
2 files changed, 43 insertions(+), 11 deletions(-)
diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index 3e6b53d6a0f1..94d5a1ebbd75 100644
--- a/gcc/gimple-fold.cc
+++ b/gcc/gimple-fold.cc
@@ -906,18 +906,41 @@ size_must_be_zero_p (tree size)
static bool
optimize_memcpy_to_memset (gimple_stmt_iterator *gsip, tree dest, tree src,
tree len)
{
+ ao_ref read;
gimple *stmt = gsi_stmt (*gsip);
if (gimple_has_volatile_ops (stmt))
return false;
- tree vuse = gimple_vuse (stmt);
- if (vuse == NULL || TREE_CODE (vuse) != SSA_NAME)
- return false;
- gimple *defstmt = SSA_NAME_DEF_STMT (vuse);
tree src2 = NULL_TREE, len2 = NULL_TREE;
poly_int64 offset, offset2;
tree val = integer_zero_node;
+ bool len_was_null = len == NULL_TREE;
+ if (len == NULL_TREE)
+ len = (TREE_CODE (src) == COMPONENT_REF
+ ? DECL_SIZE_UNIT (TREE_OPERAND (src, 1))
+ : TYPE_SIZE_UNIT (TREE_TYPE (src)));
+ if (len == NULL_TREE
+ || !poly_int_tree_p (len))
+ return false;
+
+ ao_ref_init (&read, src);
+ tree vuse = gimple_vuse (stmt);
+ gimple *defstmt;
+ do {
+ if (vuse == NULL || TREE_CODE (vuse) != SSA_NAME)
+ return false;
+ defstmt = SSA_NAME_DEF_STMT (vuse);
+ if (is_a <gphi*>(defstmt))
+ return false;
+
+ /* If the len was null, then we can use TBBA. */
+ if (stmt_may_clobber_ref_p_1 (defstmt, &read,
+ /* tbaa_p = */ len_was_null))
+ break;
+ vuse = gimple_vuse (defstmt);
+ } while (true);
+
if (gimple_store_p (defstmt)
&& gimple_assign_single_p (defstmt)
&& TREE_CODE (gimple_assign_rhs1 (defstmt)) == STRING_CST
@@ -956,17 +979,11 @@ optimize_memcpy_to_memset (gimple_stmt_iterator *gsip,
tree dest, tree src, tree
if (src2 == NULL_TREE)
return false;
- if (len == NULL_TREE)
- len = (TREE_CODE (src) == COMPONENT_REF
- ? DECL_SIZE_UNIT (TREE_OPERAND (src, 1))
- : TYPE_SIZE_UNIT (TREE_TYPE (src)));
if (len2 == NULL_TREE)
len2 = (TREE_CODE (src2) == COMPONENT_REF
? DECL_SIZE_UNIT (TREE_OPERAND (src2, 1))
: TYPE_SIZE_UNIT (TREE_TYPE (src2)));
- if (len == NULL_TREE
- || !poly_int_tree_p (len)
- || len2 == NULL_TREE
+ if (len2 == NULL_TREE
|| !poly_int_tree_p (len2))
return false;
diff --git a/gcc/testsuite/gcc.dg/pr118947-1.c
b/gcc/testsuite/gcc.dg/pr118947-1.c
new file mode 100644
index 000000000000..70b7f800065c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118947-1.c
@@ -0,0 +1,15 @@
+/* PR tree-optimization/118947 */
+/* { dg-do compile { target size32plus } } */
+/* { dg-options "-O2 -fdump-tree-forwprop1-details" } */
+/* { dg-final { scan-tree-dump-times "after previous" 1 "forwprop1" } } */
+
+void* aaa();
+void* bbb()
+{
+ char buf[32] = {};
+ /* Tha call to aaa should not matter and clobber buf. */
+ void* ret = aaa();
+ __builtin_memcpy(ret, buf, 32);
+ return ret;
+}
+
