This PR isn't really a C++ issue; it affects C as well, and presumably
all other languages. A comment a few lines down says
/* Avoid returning a negative bitpos as this may wreak havoc later. */
but we were failing to avoid that in this case.
Tested x86_64-pc-linux-gnu. OK for trunk/4.8?
commit 168f0f28cf3986d0e067b640031a8baaee2d09a4
Author: Jason Merrill <ja...@redhat.com>
Date: Tue Jul 9 00:06:51 2013 -0400
PR c++/57793
* expr.c (get_inner_reference): Avoid returning a negative bitpos.
diff --git a/gcc/expr.c b/gcc/expr.c
index 923f59b..bbec492 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -6733,7 +6733,7 @@ get_inner_reference (tree exp, HOST_WIDE_INT *pbitsize,
tem = tem.sext (TYPE_PRECISION (sizetype));
tem = tem.lshift (BITS_PER_UNIT == 8 ? 3 : exact_log2 (BITS_PER_UNIT));
tem += bit_offset;
- if (tem.fits_shwi ())
+ if (tem.fits_shwi () && !tem.is_negative())
{
*pbitpos = tem.to_shwi ();
*poffset = offset = NULL_TREE;
diff --git a/gcc/testsuite/c-c++-common/pr57793.c b/gcc/testsuite/c-c++-common/pr57793.c
new file mode 100644
index 0000000..7858a27
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr57793.c
@@ -0,0 +1,23 @@
+/* PR c++/57793 */
+
+struct A { unsigned a : 1; unsigned b : 1; };
+struct B
+{
+ unsigned char c[0x40000000];
+ unsigned char d[0x40000ff0];
+ struct A e;
+};
+
+void *foo (struct B *p)
+{
+ if (p->e.a)
+ return (void *) 0;
+ p->e.b = 1;
+ return p->c;
+}
+
+void
+bar (struct B *p)
+{
+ foo (p);
+}
