diff mbox series

i386: Avoid splitting 16/32-bit volatile mem test into 8-bit test [PR125180]

Message ID afmiG6Zusdk-59II@tucnak
State New
Headers
Series i386: Avoid splitting 16/32-bit volatile mem test into 8-bit test [PR125180] |

Commit Message

Jakub Jelinek May 5, 2026, 7:54 a.m. UTC 
  Hi!

With -ffuse-ops-with-volatile-access which is now even on by default
thie splitter can split a 16 or 32-bit volatile memory test into
an 8-bit volatile memory test, which is undesirable and e.g. when
it refers to some memory mapped hw registers it could misbehave.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
ok for trunk/16.2?

2026-05-05  Jakub Jelinek  <jakub@redhat.com>

	PR target/125180
	* config/i386/i386.md (HI/SI test -> QI test splitter): Punt if
	operands[2] is a volatile MEM.

	* gcc.target/i386/pr125180.c: New test.


	Jakub

Comments

Uros Bizjak May 5, 2026, 8:10 a.m. UTC | #1 
On Tue, May 5, 2026 at 9:54 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> Hi!
>
> With -ffuse-ops-with-volatile-access which is now even on by default
> thie splitter can split a 16 or 32-bit volatile memory test into
> an 8-bit volatile memory test, which is undesirable and e.g. when
> it refers to some memory mapped hw registers it could misbehave.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
> ok for trunk/16.2?
>
> 2026-05-05  Jakub Jelinek  <jakub@redhat.com>
>
>         PR target/125180
>         * config/i386/i386.md (HI/SI test -> QI test splitter): Punt if
>         operands[2] is a volatile MEM.
>
>         * gcc.target/i386/pr125180.c: New test.

OK for mainline and backports.

Thanks,
Uros.

>
> --- gcc/config/i386/i386.md.jj  2026-04-30 10:18:13.812688945 +0200
> +++ gcc/config/i386/i386.md     2026-05-04 17:40:00.188612108 +0200
> @@ -12772,6 +12772,7 @@ (define_split
>     "reload_completed
>      && GET_MODE (operands[2]) != QImode
>      && (!REG_P (operands[2]) || ANY_QI_REG_P (operands[2]))
> +    && !(MEM_P (operands[2]) && MEM_VOLATILE_P (operands[2]))
>      && ((ix86_match_ccmode (insn, CCZmode)
>          && !(INTVAL (operands[3]) & ~255))
>         || (ix86_match_ccmode (insn, CCNOmode)
> --- gcc/testsuite/gcc.target/i386/pr125180.c.jj 2026-05-04 17:47:37.651134771 +0200
> +++ gcc/testsuite/gcc.target/i386/pr125180.c    2026-05-04 17:47:19.826426119 +0200
> @@ -0,0 +1,14 @@
> +/* PR target/125180 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -masm=att" } */
> +/* { dg-final { scan-assembler "\ttestl\t\\\$1, \\\(" } } */
> +/* { dg-final { scan-assembler-not "\ttestb\t\\\$1, \\\(" } } */
> +
> +void foo (void);
> +
> +void
> +bar (unsigned volatile *x)
> +{
> +  if (*x & 1)
> +    foo ();
> +}
>
>         Jakub
>
diff mbox series

Patch

--- gcc/config/i386/i386.md.jj	2026-04-30 10:18:13.812688945 +0200
+++ gcc/config/i386/i386.md	2026-05-04 17:40:00.188612108 +0200
@@ -12772,6 +12772,7 @@  (define_split
    "reload_completed
     && GET_MODE (operands[2]) != QImode
     && (!REG_P (operands[2]) || ANY_QI_REG_P (operands[2]))
+    && !(MEM_P (operands[2]) && MEM_VOLATILE_P (operands[2]))
     && ((ix86_match_ccmode (insn, CCZmode)
 	 && !(INTVAL (operands[3]) & ~255))
 	|| (ix86_match_ccmode (insn, CCNOmode)
--- gcc/testsuite/gcc.target/i386/pr125180.c.jj	2026-05-04 17:47:37.651134771 +0200
+++ gcc/testsuite/gcc.target/i386/pr125180.c	2026-05-04 17:47:19.826426119 +0200
@@ -0,0 +1,14 @@ 
+/* PR target/125180 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -masm=att" } */
+/* { dg-final { scan-assembler "\ttestl\t\\\$1, \\\(" } } */
+/* { dg-final { scan-assembler-not "\ttestb\t\\\$1, \\\(" } } */
+
+void foo (void);
+
+void
+bar (unsigned volatile *x)
+{
+  if (*x & 1)
+    foo ();
+}