c-family: Fix ICE in get_atomic_generic_size [PR96545]

As the testcase shows, we would ICE if the type of the first argument of
various atomic builtins was pointer to (non-void) incomplete type, we would
assume that TYPE_SIZE_UNIT must be non-NULL.  This patch diagnoses it
instead.  And also changes the TREE_CODE != INTEGER_CST check to
!tree_fits_uhwi_p, as we use tree_to_uhwi after this and at least in theory
the int could be too large and not fit.

2020-08-11  Jakub Jelinek  <jakub@redhat.com>

	PR c/96545
	* c-common.c (get_atomic_generic_size): Require that first argument's
	type points to a complete type and use tree_fits_uhwi_p instead of
	just INTEGER_CST TREE_CODE check for the TYPE_SIZE_UNIT.

	* c-c++-common/pr96545.c: New test.

1 files changed, 31 insertions, 0 deletions

diff --git a/gcc/testsuite/c-c++-common/pr96545.c b/gcc/testsuite/c-c++-common/pr96545.c
new file mode 100644
index 00000000000..bc6b0cf345c
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr96545.c
@@ -0,0 +1,31 @@
+/* PR c/96545 */
+/* { dg-do compile } */
+
+extern char x[], y[], z[];
+struct S;
+extern struct S s, t, u;
+int v, w;
+
+void
+foo (void)
+{
+  __atomic_exchange (&x, &y, &z, 0);	/* { dg-error "must be a pointer to a complete type" } */
+}
+
+void
+bar (void)
+{
+  __atomic_exchange (&s, &t, &u, 0);	/* { dg-error "must be a pointer to a complete type" } */
+}
+
+void
+baz (void)
+{
+  __atomic_exchange (&v, &t, &w, 0);	/* { dg-error "size mismatch in argument 2 of" } */
+}
+
+void
+qux (void)
+{
+  __atomic_exchange (&v, &w, &t, 0);	/* { dg-error "size mismatch in argument 3 of" } */
+}