fold-const: Optimize &"foo"[0] == "foo" [PR89074]
Commit Message
Hi!
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.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2022-01-18 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.
Jakub
Comments
> Am 19.01.2022 um 00:50 schrieb Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org>:
>
> Hi!
>
> 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.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok.
Thanks,
Richard
> 2022-01-18 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.
>
> --- gcc/fold-const.cc.jj 2022-01-18 13:25:08.057491249 +0100
> +++ gcc/fold-const.cc 2022-01-18 13:53:26.106261913 +0100
> @@ -16587,6 +16587,15 @@ address_compare (tree_code code, tree ty
> || 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
> --- gcc/testsuite/gcc.dg/tree-ssa/pr89074.c.jj 2022-01-18 18:42:05.125004996 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr89074.c 2022-01-18 18:43:39.249694890 +0100
> @@ -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;
> +}
>
> Jakub
>
@@ -16587,6 +16587,15 @@ address_compare (tree_code code, tree ty
|| 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
@@ -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;
+}