Hi!
The following testcase triggers UB in simplify_binary_operation_1,
in particular trueop1 is 2 and it is shifted up by 63. Later we want
to shift it down (arithmetically) again by 63 and compare against the
original value and only optimize if there is match, i.e. if trueop1
can be safely shifted up. In cases it can't we don't want to trigger
UB, so the following patch just uses unsigned shift that is well defined
and then implementation defined conversion to signed type we rely on
everywhere. We still want mask to be signed so that the right shift
is arithmetic.
Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk as
obvious.
2017-04-11 Jakub Jelinek <ja...@redhat.com>
PR middle-end/80100
* simplify-rtx.c (simplify_binary_operation_1) <case IOR>: Perform
left shift in unsigned HOST_WIDE_INT type.
* gcc.dg/pr80100.c: New test.
--- gcc/simplify-rtx.c.jj 2017-04-11 16:09:22.003071899 +0200
+++ gcc/simplify-rtx.c 2017-04-11 16:01:44.350830295 +0200
@@ -2741,8 +2741,8 @@ simplify_binary_operation_1 (enum rtx_co
&& CONST_INT_P (XEXP (op0, 1))
&& INTVAL (XEXP (op0, 1)) < HOST_BITS_PER_WIDE_INT)
{
- int count = INTVAL (XEXP (op0, 1));
- HOST_WIDE_INT mask = INTVAL (trueop1) << count;
+ int count = INTVAL (XEXP (op0, 1));
+ HOST_WIDE_INT mask = UINTVAL (trueop1) << count;
if (mask >> count == INTVAL (trueop1)
&& trunc_int_for_mode (mask, mode) == mask
--- gcc/testsuite/gcc.dg/pr80100.c.jj 2017-04-11 16:22:42.706047192 +0200
+++ gcc/testsuite/gcc.dg/pr80100.c 2017-04-11 16:22:29.000000000 +0200
@@ -0,0 +1,9 @@
+/* PR middle-end/80100 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+long int
+foo (long int x)
+{
+ return 2L | ((x - 1L) >> (__SIZEOF_LONG__ * __CHAR_BIT__ - 1));
+}
Jakub
