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

[Jakub Jelinek]

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  <ja...@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.

--- 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