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 --git a/gcc/combine.c b/gcc/combine.c
index 3294575357bfcb19e589868da34364498a860dcf..dffa3b0390b582f805be7e014baad085eb89c32b 100644 (file)
--- 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 (file)
index 0000000..75226f5
--- /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;
+}