[gcc r12-2830] Evaluate arguments of sizeof that are structs of variable size.

[Martin Uecker <uecker@gcc.gnu.org>]

https://gcc.gnu.org/g:0631faf87a197145acd833249bf8f20a1c4aaabf

commit r12-2830-g0631faf87a197145acd833249bf8f20a1c4aaabf
Author: Martin Uecker <muecker@gwdg.de>
Date:   Tue Aug 10 07:42:51 2021 +0200

    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:
---
 gcc/c/c-typeck.c                   |  2 +-
 gcc/testsuite/gcc.dg/vla-stexp-1.c | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 5d6565bdaa9..c5bf3372321 100644
--- 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
index 00000000000..97d66937e9a
--- /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;
+}