[backport gcc-4.8/trunk r192759 <mikpe@it.uu.se>]

gcc/

2012-10-24  Jakub Jelinek  <jakub@redhat.com>

	PR debug/54828
	* gimple.h (is_gimple_sizepos): New inline function.
	* gimplify.c (gimplify_one_sizepos): Use it.  Remove useless
	final assignment to expr variable.
	* tree.c (RETURN_TRUE_IF_VAR): Return true also if
	!TYPE_SIZES_GIMPLIFIED (type) and _t is going to be gimplified
	into a local temporary.

gcc/testsuite/

2012-10-24  Jakub Jelinek  <jakub@redhat.com>

	PR debug/54828
	* g++.dg/debug/pr54828.C: New test.

--- gcc-4.6.3/gcc/gimple.h.~1~	2011-04-18 23:58:03.000000000 +0200
+++ gcc-4.6.3/gcc/gimple.h	2012-10-27 12:41:32.000000000 +0200
@@ -1031,6 +1031,24 @@ struct gimplify_ctx
   bool allow_rhs_cond_expr;
 };
 
+/* Return true if gimplify_one_sizepos doesn't need to gimplify
+   expr (when in TYPE_SIZE{,_UNIT} and similar type/decl size/bitsize
+   fields).  */
+static inline bool
+is_gimple_sizepos (tree expr)
+{
+  /* gimplify_one_sizepos doesn't need to do anything if the value isn't there,
+     is constant, or contains A PLACEHOLDER_EXPR.  We also don't want to do
+     anything if it's already a VAR_DECL.  If it's a VAR_DECL from another
+     function, the gimplifier will want to replace it with a new variable,
+     but that will cause problems if this type is from outside the function.
+     It's OK to have that here.  */
+  return (expr == NULL_TREE
+	  || TREE_CONSTANT (expr)
+	  || TREE_CODE (expr) == VAR_DECL
+	  || CONTAINS_PLACEHOLDER_P (expr));
+}                                        
+
 extern enum gimplify_status gimplify_expr (tree *, gimple_seq *, gimple_seq *,
 					   bool (*) (tree), fallback_t);
 extern void gimplify_type_sizes (tree, gimple_seq *);
--- gcc-4.6.3/gcc/gimplify.c.~1~	2011-07-07 14:50:03.000000000 +0200
+++ gcc-4.6.3/gcc/gimplify.c	2012-10-27 12:41:32.000000000 +0200
@@ -7658,9 +7658,7 @@ gimplify_one_sizepos (tree *expr_p, gimp
      a VAR_DECL.  If it's a VAR_DECL from another function, the gimplifier
      will want to replace it with a new variable, but that will cause problems
      if this type is from outside the function.  It's OK to have that here.  */
-  if (expr == NULL_TREE || TREE_CONSTANT (expr)
-      || TREE_CODE (expr) == VAR_DECL
-      || CONTAINS_PLACEHOLDER_P (expr))
+  if (is_gimple_sizepos (expr))
     return;
 
   type = TREE_TYPE (expr);
--- gcc-4.6.3/gcc/testsuite/g++.dg/debug/pr54828.C.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6.3/gcc/testsuite/g++.dg/debug/pr54828.C	2012-10-27 12:41:32.000000000 +0200
@@ -0,0 +1,14 @@
+// PR debug/54828
+// { dg-do compile }
+// { dg-options "-g" }
+
+struct T { T (); virtual ~T (); };
+struct S : public virtual T { S (); virtual ~S (); };
+int v;
+void foo (char *);
+
+S::S ()
+{
+  char s[v];
+  foo (s);
+}
--- gcc-4.6.3/gcc/tree.c.~1~	2011-07-18 21:45:21.000000000 +0200
+++ gcc-4.6.3/gcc/tree.c	2012-10-27 12:42:19.000000000 +0200
@@ -8257,11 +8257,18 @@ variably_modified_type_p (tree type, tre
   tree t;
 
 /* Test if T is either variable (if FN is zero) or an expression containing
-   a variable in FN.  */
+   a variable in FN.  If TYPE isn't gimplified, return true also if
+   gimplify_one_sizepos would gimplify the expression into a local
+   variable.  */
 #define RETURN_TRUE_IF_VAR(T)						\
   do { tree _t = (T);							\
-    if (_t && _t != error_mark_node && TREE_CODE (_t) != INTEGER_CST	\
-        && (!fn || walk_tree (&_t, find_var_from_fn, fn, NULL)))	\
+    if (_t != NULL_TREE							\
+	&& _t != error_mark_node					\
+	&& TREE_CODE (_t) != INTEGER_CST				\
+	&& (!fn								\
+	    || (!TYPE_SIZES_GIMPLIFIED (type)				\
+		&& !is_gimple_sizepos (_t))				\
+	    || walk_tree (&_t, find_var_from_fn, fn, NULL)))		\
       return true;  } while (0)
 
   if (type == error_mark_node)