[PATCH PR66638]Fix assertion failure by skip the case.

[Bin Cheng]

Hi,
This patch fixes GCC's profiled bootstrap failure.  As comment added by in
patch, it may still be possible to prove no overflow information for some
scev, unfortunately it's a rare case observed during GCC profiled bootstrap.
So for now I just skip it.

Is this OK?

Thanks,
bin

2015-06-26  Bin Cheng  <bin.ch...@arm.com>

        PR bootstrap/66638
        * tree-ssa-loop-niter.c (loop_exits_before_overflow): Skip if
        assertion failed.  Remove assertion itself.


Index: gcc/tree-ssa-loop-niter.c
===================================================================
--- gcc/tree-ssa-loop-niter.c   (revision 224827)
+++ gcc/tree-ssa-loop-niter.c   (working copy)
@@ -3955,7 +3955,21 @@ loop_exits_before_overflow (tree base, tree step,
        if (!CONVERT_EXPR_P (e) || !operand_equal_p (e, unsigned_base, 0))
          continue;
        e = TREE_OPERAND (e, 0);
-       gcc_assert (operand_equal_p (e, base, 0));
+       /* It may still be possible to prove no overflow even if condition
+          "operand_equal_p (e, base, 0)" isn't satisfied here, like below
+          example:
+
+            e             : ssa_var                 ; unsigned long type
+            base          : (int) ssa_var
+            unsigned_base : (unsigned int) ssa_var
+
+          Unfortunately this is a rare case observed during GCC profiled
+          bootstrap.  See PR66638 for more information.
+
+          For now, we just skip the possibility.  */
+       if (!operand_equal_p (e, base, 0))
+         continue;
+
        if (tree_int_cst_sign_bit (step))
          {
            code = LT_EXPR;