The following fixes phiopt to not introduce undefined behavior
in its abs replacement code in case we negate only positive values
in the original code.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2016-11-07 Richard Biener <rguent...@suse.de>
PR tree-optimization/78228
* tree-ssa-phiopt.c (abs_replacement): Avoid introducing
undefined behavior.
* gcc.dg/tree-ssa/phi-opt-15.c: New testcase.
Index: gcc/tree-ssa-phiopt.c
===================================================================
--- gcc/tree-ssa-phiopt.c (revision 241891)
+++ gcc/tree-ssa-phiopt.c (working copy)
@@ -1453,6 +1453,14 @@ abs_replacement (basic_block cond_bb, ba
else
negate = false;
+ /* If the code negates only iff positive then make sure to not
+ introduce undefined behavior when negating or computing the absolute.
+ ??? We could use range info if present to check for arg1 == INT_MIN. */
+ if (negate
+ && (ANY_INTEGRAL_TYPE_P (TREE_TYPE (arg1))
+ && ! TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg1))))
+ return false;
+
result = duplicate_ssa_name (result, NULL);
if (negate)
Index: gcc/testsuite/gcc.dg/tree-ssa/phi-opt-15.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/phi-opt-15.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/phi-opt-15.c (working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int
+foo (int i)
+{
+ if (i > 0)
+ i = -i;
+ return i;
+}
+
+/* { dg-final { scan-tree-dump-not "ABS" "optimized" } } */
