[PATCH][match-and-simplify] Fix some C++ testsuite FAILs

[Richard Biener <rguenther at suse dot de>]

The following fixes C++ testsuite FAILs.  First in fold_binary
we should delay the dispatch to generic_simplify until after
const OP const folding which generic_simplify isn't supposed
to do.  (I note that neither fold_unary nor fold_ternary has
such clear const operand path...)

Second, the C++ FE folds too early and some testcases expect
to detect sizeof (&a) + 0 in some way (didn't look).  Wrapping
the result in a NON_LVALUE_EXPR works around the issue
(though certainly sizeof (&a) shouldn't be considered an
lvalue by maybe_lvalue_p).

Full testing pending on x86_64-unknown-linux-gnu.

Richard.

2014-08-26  Richard Biener  <rguenther@suse.de>

	* fold-const.c (fold_binary_loc): Move dispatch to
	generic_simplfy after folding of operations on two constants.
	* match-constant-folding.pd (x + 0 -> x): Wrap result in
	a NON_LVALUE_EXPR to account for the C++ frontend folding
	too early, avoding some spurious testsuite FAILs.

Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c	(revision 214490)
+++ gcc/fold-const.c	(working copy)
@@ -10068,11 +10067,6 @@ fold_binary_loc (location_t loc,
 	      && op0 != NULL_TREE
 	      && op1 != NULL_TREE);
 
-  extern tree generic_simplify (enum tree_code, tree, tree, tree);
-  tem = generic_simplify (code, type, op0, op1);
-  if (tem)
-    return tem;
-
   arg0 = op0;
   arg1 = op1;
 
@@ -10130,6 +10124,11 @@ fold_binary_loc (location_t loc,
 	}
     }
 
+  extern tree generic_simplify (enum tree_code, tree, tree, tree);
+  tem = generic_simplify (code, type, op0, op1);
+  if (tem)
+    return tem;
+
   /* If this is a commutative operation, and ARG0 is a constant, move it
      to ARG1 to reduce the number of tests below.  */
   if (commutative_tree_code (code)
Index: gcc/match-constant-folding.pd
===================================================================
--- gcc/match-constant-folding.pd	(revision 214490)
+++ gcc/match-constant-folding.pd	(working copy)
@@ -20,7 +20,17 @@ along with GCC; see the file COPYING3.
 (for op in plus pointer_plus minus bit_ior bit_xor
   (simplify
     (op @0 integer_zerop)
-    @0))
+#if GENERIC
+    /* ???  fold_binary adds non_lvalue here and "fixes" the C++
+       run of Wsizeof-pointer-memaccess1.c, preserving enough of
+       sizeof (&a) + 0 because sizeof (&a) is maybe_lvalue_p ()
+       for no good reason.  The C frontend is fine as it doesn't
+       fold too early.  */
+    (non_lvalue @0)
+#else
+    @0
+#endif
+  ))
 
 (simplify
   (minus @0 @0)