From 0631faf87a197145acd833249bf8f20a1c4aaabf Mon Sep 17 00:00:00 2001
From: Martin Uecker <muecker@gwdg.de>
Date: Tue, 10 Aug 2021 07:42:51 +0200
Subject: [PATCH] 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.
---
 gcc/c/c-typeck.c                   |  2 +-
 gcc/testsuite/gcc.dg/vla-stexp-1.c | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/vla-stexp-1.c

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;
+}