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[PATCH] Don't simplify_conversion_from_bitmask on x & 1 (PR tree-optimization/59014)
- From: Marek Polacek <polacek at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: Jeff Law <law at redhat dot com>
- Date: Thu, 7 Nov 2013 16:15:11 +0100
- Subject: [PATCH] Don't simplify_conversion_from_bitmask on x & 1 (PR tree-optimization/59014)
- Authentication-results: sourceware.org; auth=none
Here, forward propagation turned
_6 = a.1_5 & 1;
_7 = (_Bool) _6;
into
_7 = (_Bool) a.1_5;
but that's wrong: e.g. if a = 2 then (_Bool) _6 is 0, but (_Bool) a.1_5 is 1.
If a is an odd number, this is correct, but we don't know the value
of a, so I disabled this optimization for "x & 1" cases. For e.g. "x & 255",
this still works correctly.
In this PR, VRP created wrong ASSERT_EXPR because of this, thus we were
miscompiling the following testcase...
Regtested/bootstrapped on x86_64-linux, ok for trunk?
2013-11-07 Marek Polacek <polacek@redhat.com>
PR tree-optimization/59014
* tree-ssa-forwprop.c (simplify_conversion_from_bitmask): Don't
optimize x & 1 expressions here.
testsuite/
* gcc.dg/torture/pr59014.c: New test.
--- gcc/testsuite/gcc.dg/torture/pr59014.c.mp 2013-11-07 14:47:38.040941144 +0100
+++ gcc/testsuite/gcc.dg/torture/pr59014.c 2013-11-07 14:49:03.646271031 +0100
@@ -0,0 +1,26 @@
+/* PR tree-optimization/59014 */
+/* { dg-do run } */
+
+int a = 2, b, c, d;
+
+int
+foo ()
+{
+ for (;; c++)
+ if ((b > 0) | (a & 1))
+ ;
+ else
+ {
+ d = a;
+ return 0;
+ }
+}
+
+int
+main ()
+{
+ foo ();
+ if (d != 2)
+ __builtin_abort ();
+ return 0;
+}
--- gcc/tree-ssa-forwprop.c.mp 2013-11-07 14:30:43.785733810 +0100
+++ gcc/tree-ssa-forwprop.c 2013-11-07 14:42:31.836765375 +0100
@@ -1199,9 +1199,16 @@ simplify_conversion_from_bitmask (gimple
if (TREE_CODE (rhs_def_operand1) == SSA_NAME
&& ! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs_def_operand1)
&& TREE_CODE (rhs_def_operand2) == INTEGER_CST
+ /* We can't turn
+ _6 = a & 1;
+ _7 = (_Bool) _6;
+ into
+ _7 = (_Bool) a;
+ as that's wrong if A is an even number. */
+ && ! integer_onep (rhs_def_operand2)
&& operand_equal_p (rhs_def_operand2,
build_low_bits_mask (TREE_TYPE (rhs_def_operand2),
- TYPE_PRECISION (lhs_type)),
+ TYPE_PRECISION (lhs_type)),
0))
{
/* This is an optimizable case. Replace the source operand
Marek