diff mbox series

i386: Fix up the vzeroupper REG_DEAD/REG_UNUSED note workaround [PR114190]

Message ID Zegk0SwZ8KtO1E8V@tucnak
State New
Headers show
Series i386: Fix up the vzeroupper REG_DEAD/REG_UNUSED note workaround [PR114190] | expand

Commit Message

Jakub Jelinek March 6, 2024, 8:09 a.m. UTC 
Hi!

When writing the rest_of_handle_insert_vzeroupper workaround to manually
remove all the REG_DEAD/REG_UNUSED notes from the IL, I've missed that
there is a df_analyze () call right after it and that the problems added
earlier in the pass, like df_note_add_problem () done during mode switching,
doesn't affect just the next df_analyze () call right after it, but all
other df_analyze () calls until the end of the current pass where
df_finish_pass removes the optional problems.

So, as can be seen on the following patch, the workaround doesn't actually
work there, because while rest_of_handle_insert_vzeroupper carefully removes
all REG_DEAD/REG_UNUSED notes, the df_analyze () call at the end of the
function immediately adds them in again (so, I must say I have no idea
why the workaround worked on the earlier testcases).

Now, I could move the df_analyze () call just before the REG_DEAD/REG_UNUSED
note removal loop, but I think the following patch is better, because
the df_analyze () call doesn't have to recompute the problem when we don't
care about it and will actively strip all traces of it away.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2024-03-06  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/114190
	* config/i386/i386-features.cc (rest_of_handle_insert_vzeroupper):
	Call df_remove_problem for df_note before calling df_analyze.

	* gcc.target/i386/avx-pr114190.c: New test.


	Jakub

Comments

Uros Bizjak March 6, 2024, 8:32 a.m. UTC | #1 
On Wed, Mar 6, 2024 at 9:10 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> Hi!
>
> When writing the rest_of_handle_insert_vzeroupper workaround to manually
> remove all the REG_DEAD/REG_UNUSED notes from the IL, I've missed that
> there is a df_analyze () call right after it and that the problems added
> earlier in the pass, like df_note_add_problem () done during mode switching,
> doesn't affect just the next df_analyze () call right after it, but all
> other df_analyze () calls until the end of the current pass where
> df_finish_pass removes the optional problems.
>
> So, as can be seen on the following patch, the workaround doesn't actually
> work there, because while rest_of_handle_insert_vzeroupper carefully removes
> all REG_DEAD/REG_UNUSED notes, the df_analyze () call at the end of the
> function immediately adds them in again (so, I must say I have no idea
> why the workaround worked on the earlier testcases).
>
> Now, I could move the df_analyze () call just before the REG_DEAD/REG_UNUSED
> note removal loop, but I think the following patch is better, because
> the df_analyze () call doesn't have to recompute the problem when we don't
> care about it and will actively strip all traces of it away.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2024-03-06  Jakub Jelinek  <jakub@redhat.com>
>
>         PR rtl-optimization/114190
>         * config/i386/i386-features.cc (rest_of_handle_insert_vzeroupper):
>         Call df_remove_problem for df_note before calling df_analyze.
>
>         * gcc.target/i386/avx-pr114190.c: New test.

OK.

Thanks,
Uros.

>
> --- gcc/config/i386/i386-features.cc.jj 2024-02-22 10:10:18.658032517 +0100
> +++ gcc/config/i386/i386-features.cc    2024-03-05 09:23:54.496112264 +0100
> @@ -2690,6 +2690,7 @@ rest_of_handle_insert_vzeroupper (void)
>             }
>         }
>
> +  df_remove_problem (df_note);
>    df_analyze ();
>    return 0;
>  }
> --- gcc/testsuite/gcc.target/i386/avx-pr114190.c.jj     2024-03-05 10:07:24.869454305 +0100
> +++ gcc/testsuite/gcc.target/i386/avx-pr114190.c        2024-03-05 10:06:52.870889687 +0100
> @@ -0,0 +1,27 @@
> +/* PR rtl-optimization/114190 */
> +/* { dg-do run { target avx } } */
> +/* { dg-options "-O2 -fno-dce -fharden-compares -mavx --param=max-rtl-if-conversion-unpredictable-cost=136 -mno-avx512f -Wno-psabi" } */
> +
> +#include "avx-check.h"
> +
> +typedef unsigned char U __attribute__((vector_size (64)));
> +typedef unsigned int V __attribute__((vector_size (64)));
> +U u;
> +
> +V
> +foo (V a, V b)
> +{
> +  u[0] = __builtin_sub_overflow (0, (int) a[0], &a[b[7] & 5]) ? -u[1] : -b[3];
> +  b ^= 0 != b;
> +  return (V) u + (V) a + (V) b;
> +}
> +
> +static void
> +avx_test (void)
> +{
> +  V x = foo ((V) { 1 }, (V) { 0, 0, 0, 1 });
> +  if (x[0] != -1U)
> +    __builtin_abort ();
> +  if (x[3] != -2U)
> +    __builtin_abort ();
> +}
>
>         Jakub
>
diff mbox series

Patch

--- gcc/config/i386/i386-features.cc.jj	2024-02-22 10:10:18.658032517 +0100
+++ gcc/config/i386/i386-features.cc	2024-03-05 09:23:54.496112264 +0100
@@ -2690,6 +2690,7 @@  rest_of_handle_insert_vzeroupper (void)
 	    }
 	}
 
+  df_remove_problem (df_note);
   df_analyze ();
   return 0;
 }
--- gcc/testsuite/gcc.target/i386/avx-pr114190.c.jj	2024-03-05 10:07:24.869454305 +0100
+++ gcc/testsuite/gcc.target/i386/avx-pr114190.c	2024-03-05 10:06:52.870889687 +0100
@@ -0,0 +1,27 @@ 
+/* PR rtl-optimization/114190 */
+/* { dg-do run { target avx } } */
+/* { dg-options "-O2 -fno-dce -fharden-compares -mavx --param=max-rtl-if-conversion-unpredictable-cost=136 -mno-avx512f -Wno-psabi" } */
+
+#include "avx-check.h"
+
+typedef unsigned char U __attribute__((vector_size (64)));
+typedef unsigned int V __attribute__((vector_size (64)));
+U u;
+
+V
+foo (V a, V b)
+{
+  u[0] = __builtin_sub_overflow (0, (int) a[0], &a[b[7] & 5]) ? -u[1] : -b[3];
+  b ^= 0 != b;
+  return (V) u + (V) a + (V) b;
+}
+
+static void
+avx_test (void)
+{
+  V x = foo ((V) { 1 }, (V) { 0, 0, 0, 1 });
+  if (x[0] != -1U)
+    __builtin_abort ();
+  if (x[3] != -2U)
+    __builtin_abort ();
+}