[pushed] c++: lvalue_kind tweak

[Jason Merrill <jason@redhat.com>]

Tested x86_64-pc-linux-gnu, applying to trunk.

-- >8 --

I was wondering how lvalue_kind handles VIEW_CONVERT_EXPR; in cases where
the type actually changes, it should have the same prvalue->xvalue effect as
ARRAY_REF, since we need to materialize a temporary to get an object we can
reinterpret as another type.

Currently this only fires on builtin-shufflevector-3.c, where we use
VIEW_CONVERT_EXPR to reinterpret a vector as an array.

REALPART_EXPR and IMAGPART_EXPR should also be treated like COMPONENT_REF.
PREINCREMENT_EXPR and PREDECREMENT_EXPR should only be applied to glvalues,
but if for some reason they were applied to a prvalue this would be correct.
TRY_CATCH_EXPR around a prvalue is also questionable, but this is the right
handling.

gcc/cp/ChangeLog:

	* tree.cc (lvalue_kind) [VIEW_CONVERT_EXPR]: Change prvalue to
	xvalue.
---
 gcc/cp/tree.cc | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index aa9c1b7d8f9..6d968a2af11 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -104,7 +104,17 @@ lvalue_kind (const_tree ref)
     case REALPART_EXPR:
     case IMAGPART_EXPR:
     case VIEW_CONVERT_EXPR:
-      return lvalue_kind (TREE_OPERAND (ref, 0));
+      op1_lvalue_kind = lvalue_kind (TREE_OPERAND (ref, 0));
+      /* As for ARRAY_REF and COMPONENT_REF, these codes turn a class prvalue
+	 into an xvalue: we need to materialize the temporary before we mess
+	 with it.  Except VIEW_CONVERT_EXPR that doesn't actually change the
+	 type, as in location wrapper and REF_PARENTHESIZED_P.	*/
+      if (op1_lvalue_kind == clk_class
+	  && !(TREE_CODE (ref) == VIEW_CONVERT_EXPR
+	       && (same_type_ignoring_top_level_qualifiers_p
+		   (TREE_TYPE (ref), TREE_TYPE (TREE_OPERAND (ref, 0))))))
+	return clk_rvalueref;
+      return op1_lvalue_kind;
 
     case ARRAY_REF:
       {

base-commit: 7d935cdd1a6772699ec0ab4f93711928ca4d30a1
-- 
2.31.1