Hi!
For flexible array members we need to incrementally clear just from
ptr + total_bytes up to new ptr + total_bytes, but memset has been called
with the length from ptr, so was missing - total_bytes. Additionally,
in this code off is guaranteed to be -1 and thus o 0, so don't bother pretending
we could handle anything else, it would be more complicated than that.
Sorry for this brown paper bug, tested on x86_64-linux, committed to trunk
as obvious.
2020-12-21 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/98407
* fold-const.c (native_encode_initializer): When handling flexible
array members, fix up computation of length for memset. Also remove
" - o" as o is always guaranteed to be 0 in this code path.
* gcc.c-torture/compile/pr98407.c: New test.
--- gcc/fold-const.c.jj 2020-12-19 22:24:03.945714395 +0100
+++ gcc/fold-const.c 2020-12-21 09:59:59.715313469 +0100
@@ -8280,9 +8280,9 @@ native_encode_initializer (tree init, un
return 0;
if (pos + fieldsize > total_bytes)
{
- if (ptr != NULL && total_bytes - o < len)
- memset (ptr + (total_bytes - o),
- '\0', MIN (pos + fieldsize - o, len));
+ if (ptr != NULL && total_bytes < len)
+ memset (ptr + total_bytes, '\0',
+ MIN (pos + fieldsize, len) - total_bytes);
total_bytes = pos + fieldsize;
}
}
--- gcc/testsuite/gcc.c-torture/compile/pr98407.c.jj 2020-12-21
10:05:11.824717082 +0100
+++ gcc/testsuite/gcc.c-torture/compile/pr98407.c 2020-12-21
10:04:54.267919387 +0100
@@ -0,0 +1,10 @@
+/* PR tree-optimization/98407 */
+
+struct S { int a; int b[]; };
+const struct S c = { 0, { 0 } }, d = { 0, { 0 } };
+
+int
+foo (void)
+{
+ return __builtin_memcmp (&c, &d, sizeof d);
+}
Jakub
