Hi!
On a testcase like below which would trigger UB at runtime we trigger
UB in the compiler, by reading uninitialized bytes.
The VCE folding for which native_{encode,interpret}_expr has been originally
written passes the length from the first one to the second one, so that
the latter can return NULL_TREE (not fold) if not enough bytes in the buffer
were filled. I believe this is the shortest fix for this issue and makes
the code consistent with what is used in VCE folding.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2015-12-09 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/68785
* gimple-fold.c (fold_ctor_reference): Pass return value from
native_encode_expr to native_interpret_expr.
* tree-ssa-sccvn.c (fully_constant_vn_reference_p): Likewise.
* gcc.dg/pr68785.c: New test.
--- gcc/gimple-fold.c.jj 2015-11-24 11:43:35.000000000 +0100
+++ gcc/gimple-fold.c 2015-12-09 10:48:06.824975709 +0100
@@ -5495,9 +5495,10 @@ fold_ctor_reference (tree type, tree cto
&& size <= MAX_BITSIZE_MODE_ANY_MODE)
{
unsigned char buf[MAX_BITSIZE_MODE_ANY_MODE / BITS_PER_UNIT];
- if (native_encode_expr (ctor, buf, size / BITS_PER_UNIT,
- offset / BITS_PER_UNIT) > 0)
- return native_interpret_expr (type, buf, size / BITS_PER_UNIT);
+ int len = native_encode_expr (ctor, buf, size / BITS_PER_UNIT,
+ offset / BITS_PER_UNIT);
+ if (len > 0)
+ return native_interpret_expr (type, buf, len);
}
if (TREE_CODE (ctor) == CONSTRUCTOR)
{
--- gcc/tree-ssa-sccvn.c.jj 2015-12-04 17:19:12.000000000 +0100
+++ gcc/tree-ssa-sccvn.c 2015-12-09 10:50:30.329960789 +0100
@@ -1370,8 +1370,9 @@ fully_constant_vn_reference_p (vn_refere
else
{
unsigned char buf[MAX_BITSIZE_MODE_ANY_MODE / BITS_PER_UNIT];
- if (native_encode_expr (ctor, buf, size, off) > 0)
- return native_interpret_expr (ref->type, buf, size);
+ int len = native_encode_expr (ctor, buf, size, off);
+ if (len > 0)
+ return native_interpret_expr (ref->type, buf, len);
}
}
}
--- gcc/testsuite/gcc.dg/pr68785.c.jj 2015-12-09 10:52:00.232698487 +0100
+++ gcc/testsuite/gcc.dg/pr68785.c 2015-12-09 10:50:54.000000000 +0100
@@ -0,0 +1,9 @@
+/* PR tree-optimization/68785 */
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+int
+foo (void)
+{
+ return *(int *) "";
+}
Jakub
