[gcc r11-8139] combine: Don't fold away side-effects in simplify_and_const_int_1 [PR99830]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:9c1c8ad8339d551ac91a7af5614f29b9a687189a

commit r11-8139-g9c1c8ad8339d551ac91a7af5614f29b9a687189a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Apr 13 01:00:48 2021 +0200

    combine: Don't fold away side-effects in simplify_and_const_int_1 [PR99830]
    
    Here is an alternate patch for the PR99830 bug.
    As discussed on IRC and in the PR, the reason why a (clobber:TI (const_int 0))
    has been propagated into the debug insns is that it got optimized away
    during simplification from the i3 instruction pattern.
    
    And that happened because
    simplify_and_const_int_1 (SImode, varop, 255)
    with varop of
    (ashift:SI (subreg:SI (and:TI (clobber:TI (const_int 0 [0]))
                                  (const_int 255 [0xff])) 0)
               (const_int 16 [0x10]))
    was called and through nonzero_bits determined that (whatever << 16) & 255
    is const0_rtx.
    It is, but if there are side-effects in varop and such clobbers are
    considered as such, we shouldn't optimize those away.
    
    2021-04-13  Jakub Jelinek  <jakub@redhat.com>
    
            PR debug/99830
            * combine.c (simplify_and_const_int_1): Don't optimize varop
            away if it has side-effects.
    
            * gcc.dg/pr99830.c: New test.

Diff:
---
 gcc/combine.c                  |  2 +-
 gcc/testsuite/gcc.dg/pr99830.c | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/combine.c b/gcc/combine.c
index 3294575357b..dffa3b0390b 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -10153,7 +10153,7 @@ simplify_and_const_int_1 (scalar_int_mode mode, rtx varop,
   constop &= nonzero;
 
   /* If we don't have any bits left, return zero.  */
-  if (constop == 0)
+  if (constop == 0 && !side_effects_p (varop))
     return const0_rtx;
 
   /* If VAROP is a NEG of something known to be zero or 1 and CONSTOP is
diff --git a/gcc/testsuite/gcc.dg/pr99830.c b/gcc/testsuite/gcc.dg/pr99830.c
new file mode 100644
index 00000000000..75226f5c3a9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr99830.c
@@ -0,0 +1,10 @@
+/* PR debug/99830 */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -fno-expensive-optimizations -fno-split-wide-types -g" } */
+
+int foo (long a, __int128 b, short c, int d, unsigned e, __int128 f)
+{
+  __builtin_memmove (2 + (char *) &f, foo, 1);
+  c >>= (char) f;
+  return c;
+}