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

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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.
This commit is contained in:
Jakub Jelinek 2021-04-13 01:00:48 +02:00
parent eb49f7de93
commit 9c1c8ad833
2 changed files with 11 additions and 1 deletions
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2
gcc/combine.c
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@ -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

10
gcc/testsuite/gcc.dg/pr99830.c Normal file
View file

@ -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;
}