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* [gcc r12-6726] fold-const: Optimize &"foo"[0] == "foo" [PR89074]
@ 2022-01-19 8:26 Jakub Jelinek
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From: Jakub Jelinek @ 2022-01-19 8:26 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:b834435c8fa4cb9424787fe3044a49fef7992de8
commit r12-6726-gb834435c8fa4cb9424787fe3044a49fef7992de8
Author: Jakub Jelinek <jakub@redhat.com>
Date: Wed Jan 19 09:26:13 2022 +0100
fold-const: Optimize &"foo"[0] == "foo" [PR89074]
This is a non-C++ related part from the PR89074 address_compare changes.
For "foo" == "foo" we already optimize this from the (cmp @0 @0)
simplification, because we use operand_equal_p in that case
and operand_equal_p also compares the STRING_CSTs bytes rather than
just addresses.
2022-01-19 Jakub Jelinek <jakub@redhat.com>
PR c++/89074
* fold-const.cc (address_compare): Consider different STRING_CSTs
with the same lengths that memcmp the same as equal, not different.
* gcc.dg/tree-ssa/pr89074.c: New test.
Diff:
---
gcc/fold-const.cc | 9 +++++++++
gcc/testsuite/gcc.dg/tree-ssa/pr89074.c | 12 ++++++++++++
2 files changed, 21 insertions(+)
diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index ff6a74928a8..8fe633c03f9 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -16587,6 +16587,15 @@ address_compare (tree_code code, tree type, tree op0, tree op1,
|| TREE_CODE (base1) == SSA_NAME
|| TREE_CODE (base1) == STRING_CST))
equal = (base0 == base1);
+ /* Assume different STRING_CSTs with the same content will be
+ merged. */
+ if (equal == 0
+ && TREE_CODE (base0) == STRING_CST
+ && TREE_CODE (base1) == STRING_CST
+ && TREE_STRING_LENGTH (base0) == TREE_STRING_LENGTH (base1)
+ && memcmp (TREE_STRING_POINTER (base0), TREE_STRING_POINTER (base1),
+ TREE_STRING_LENGTH (base0)) == 0)
+ equal = 1;
if (equal == 1)
{
if (code == EQ_EXPR
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr89074.c b/gcc/testsuite/gcc.dg/tree-ssa/pr89074.c
new file mode 100644
index 00000000000..666dfa7e105
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr89074.c
@@ -0,0 +1,12 @@
+/* PR c++/89074 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump "return 1;" "optimized" } } */
+
+int
+foo (void)
+{
+ const char *a = &"foo"[0];
+ const char *b = "foo";
+ return a == b;
+}
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