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

Jakub Jelinek jakub@redhat.com
Sat Apr 10 06:02:29 GMT 2021


Hi!

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.

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

2021-04-10  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.

--- gcc/combine.c.jj	2021-04-08 17:01:37.315168182 +0200
+++ gcc/combine.c	2021-04-09 22:33:56.961264092 +0200
@@ -10153,7 +10153,7 @@ simplify_and_const_int_1 (scalar_int_mod
   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
--- gcc/testsuite/gcc.dg/pr99830.c.jj	2021-04-08 16:39:44.243774333 +0200
+++ gcc/testsuite/gcc.dg/pr99830.c	2021-04-08 16:28:40.463175738 +0200
@@ -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;
+}


	Jakub



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