Fix POINTER_PLUS_EXPR oversight

[Bernd Schmidt]

In pointer_diff we still expect pointer addition to use PLUS_EXPR. I
discovered this while working on a new port with somewhat unusual
pointer types.

Interestingly, the C++ frontend also has a pointer_diff function, but
doesn't seem to attempt to optimize. Is there a reason for this?

Bootstrapped and tested on i686-linux. Ok for now or stage1?


Bernd

        * c-typeck.c (pointer_diff): Check for POINTER_PLUS_EXPR, not
        PLUS_EXPR.

Index: gcc/c-typeck.c
===================================================================
--- gcc/c-typeck.c      (revision 183969)
+++ gcc/c-typeck.c      (working copy)
@@ -3447,7 +3447,9 @@ pointer_diff (location_t loc, tree op0,
   else
     con1 = op1;
 
-  if (TREE_CODE (con0) == PLUS_EXPR)
+  gcc_assert (TREE_CODE (con0) != PLUS_EXPR
+             && TREE_CODE (con1) != PLUS_EXPR);
+  if (TREE_CODE (con0) == POINTER_PLUS_EXPR)
     {
       lit0 = TREE_OPERAND (con0, 1);
       con0 = TREE_OPERAND (con0, 0);
@@ -3455,7 +3457,7 @@ pointer_diff (location_t loc, tree op0,
   else
     lit0 = integer_zero_node;
 
-  if (TREE_CODE (con1) == PLUS_EXPR)
+  if (TREE_CODE (con1) == POINTER_PLUS_EXPR)
     {
       lit1 = TREE_OPERAND (con1, 1);
       con1 = TREE_OPERAND (con1, 0);