Evaluate arguments of sizeof that are structs of variable size.

Evaluate arguments of sizeof for all types of variable size
and not just for VLAs. This fixes some issues related to
[PR29970] where statement expressions need to be evaluated
so that the size is well defined.

2021-08-10  Martin Uecker  <muecker@gwdg.de>

gcc/c/
	PR c/29970
	* c-typeck.c (c_expr_sizeof_expr): Evaluate
	size expressions for structs of variable size.

gcc/testsuite/
	PR c/29970
	* gcc.dg/vla-stexp-1.c: New test.

diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 5d6565bdaa936b365730f6c7a99e2b30cc40266a..c5bf3372321f5a7de8871dadc87e44f6617dc9f1 100644 (file)
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -2992,7 +2992,7 @@ c_expr_sizeof_expr (location_t loc, struct c_expr expr)
       c_last_sizeof_loc = loc;
       ret.original_code = SIZEOF_EXPR;
       ret.original_type = NULL;
-      if (c_vla_type_p (TREE_TYPE (folded_expr)))
+      if (C_TYPE_VARIABLE_SIZE (TREE_TYPE (folded_expr)))
        {
          /* sizeof is evaluated when given a vla (C99 6.5.3.4p2).  */
          ret.value = build2 (C_MAYBE_CONST_EXPR, TREE_TYPE (ret.value),

diff --git a/gcc/testsuite/gcc.dg/vla-stexp-1.c b/gcc/testsuite/gcc.dg/vla-stexp-1.c
new file mode 100644 (file)
index 0000000..97d6693
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vla-stexp-1.c
@@ -0,0 +1,18 @@
+/* PR29970*/
+/* { dg-do run } */
+/* { dg-options "-Wall -O0" } */
+
+int foo(void)
+{
+       int n = 0;
+       return sizeof(*({ n = 10; struct foo { int x[n]; } x; &x; }));
+}
+
+
+int main()
+{
+       if (sizeof(struct foo { int x[10]; }) != foo())
+               __builtin_abort();
+
+       return 0;
+}