[C PATCH] Evaluate argument of sizeof that are structs of variable size.

[Martin Uecker]

Joseph,

here is the patch for c_expr_sizeof_type you had suggested.


Best,
Martin



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  <muec...@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 --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..4d4a15d34a6
--- /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;
+}