[gcc r12-2882] Evaluate type arguments of sizeof that are structs of variable size [PR101838]

[gcc r12-2882] Evaluate type arguments of sizeof that are structs of variable size [PR101838]

[Martin Uecker]

https://gcc.gnu.org/g:d2ba65ab6010f0d507bf5512a0223692e6653b23

commit r12-2882-gd2ba65ab6010f0d507bf5512a0223692e6653b23
Author: Martin Uecker <muecker@gwdg.de>
Date:   Thu Aug 12 20:32:16 2021 +0200

    Evaluate type arguments of sizeof that are structs of variable size [PR101838]
    
    Evaluate type arguments of sizeof for all types of variable size
    and not just for VLAs. This fixes PR101838 and some issues related
    to PR29970 where statement expressions need to be evaluated so that
    the size is well defined.
    
    2021-08-12  Martin Uecker  <muecker@gwdg.de>
    
    gcc/c/
            PR c/101838
            PR c/29970
            * c-typeck.c (c_expr_sizeof_type): Evaluate
            size expressions for structs of variable size.
    
    gcc/testsuite/
            PR c/101838
            * gcc.dg/vla-stexp-2.c: New test.

Diff:
---
 gcc/c/c-typeck.c                   |  8 +++++++-
 gcc/testsuite/gcc.dg/vla-stexp-2.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index c5bf3372321..eb5c87dc57a 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -3022,8 +3022,14 @@ c_expr_sizeof_type (location_t loc, struct c_type_name *t)
   c_last_sizeof_loc = loc;
   ret.original_code = SIZEOF_EXPR;
   ret.original_type = NULL;
+  if (type == error_mark_node)
+    {
+      ret.value = error_mark_node;
+      ret.original_code = ERROR_MARK;
+    }
+  else
   if ((type_expr || TREE_CODE (ret.value) == INTEGER_CST)
-      && c_vla_type_p (type))
+      && C_TYPE_VARIABLE_SIZE (type))
     {
       /* If the type is a [*] array, it is a VLA but is represented as
 	 having a size of zero.  In such a case we must ensure that
diff --git a/gcc/testsuite/gcc.dg/vla-stexp-2.c b/gcc/testsuite/gcc.dg/vla-stexp-2.c
new file mode 100644
index 00000000000..176f400ce37
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vla-stexp-2.c
@@ -0,0 +1,33 @@
+/* PR101838 */
+/* { dg-do run } */
+/* { dg-options "-Wpedantic -O0" } */
+
+
+int bar0(
+	int (*a)[*],
+	int (*b)[sizeof(*a)]
+);
+
+
+int bar(
+	struct f { 		/* { dg-warning "will not be visible outside of this definition" } */
+		int a[*]; } v,	/* { dg-warning "variably modified type" } */
+	int (*b)[sizeof(struct f)]	// should not warn about zero size
+);
+
+int foo(void)
+{
+	int n = 0;
+	return sizeof(typeof(*({ n = 10; struct foo { 	/* { dg-warning "braced-groups" } */
+					int x[n]; 	/* { dg-warning "variably modified type" } */
+	} x; &x; })));
+}
+
+
+int main()
+{
+	if (sizeof(struct foo { int x[10]; }) != foo())
+		__builtin_abort();
+
+	return 0;
+}