Turn off copy optimization when returning a composite by reference.

The copy optimization is not correct in case of overlap between destination
and source.  We would need to use an hypothetical __builtin_memmove_aligned
that can cope with overlap to implement the copy at return of callee.

1 files changed, 39 insertions, 0 deletions

diff --git a/test/regression/struct12.c b/test/regression/struct12.c
new file mode 100644
index 00000000..39e62b28
--- /dev/null
+++ b/test/regression/struct12.c
@@ -0,0 +1,39 @@
+/*  This is was originally a regression test for bug 43784 of gcc.
+    See ISO/IEC 9899:TC3 §6.8.6.4p4 and footnote 139. */
+
+#include <stdio.h>
+
+struct s {
+  unsigned char a[256];
+};
+union u {
+  struct { struct s b; int c; } d;
+  struct { int c; struct s b; } e;
+};
+
+static union u v;
+static struct s *p = &v.d.b;
+static struct s *q = &v.e.b;
+
+static struct s __attribute__((noinline)) rp(void)
+{
+  return *p;
+}
+
+static void qp(void)
+{
+  *q = rp();
+}
+
+int main()
+{
+  int i;
+  for (i = 0; i < 256; i++)
+    p->a[i] = i;
+  qp();
+  for (i = 0; i < 256; i++)
+    if (q->a[i] != i)
+      printf("ERROR at %d: %d\n", i, q->a[i]);
+  return 0;
+}
+