[InstCombine] Minor optimization for bswap with binary ops

Added instcombine optimizations for BSWAP with AND/OR/XOR ops:

OP( BSWAP(x), BSWAP(y) ) -> BSWAP( OP(x, y) )
OP( BSWAP(x), CONSTANT ) -> BSWAP( OP(x, BSWAP(CONSTANT) ) )

Since its just a one liner, I've also added BSWAP to the DAGCombiner equivalent as well:

fold (OP (bswap x), (bswap y)) -> (bswap (OP x, y))

Refactored bswap-fold tests to use FileCheck instead of just checking that the bswaps had gone.

Differential Revision: http://reviews.llvm.org/D6407

llvm-svn: 223349
diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index 05ce02a92..4ccda4d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -402,6 +402,7 @@
                                     APInt &UndefElts, unsigned Depth = 0);
 
   Value *SimplifyVectorOp(BinaryOperator &Inst);
+  Value *SimplifyBSwap(BinaryOperator &Inst);
 
   // FoldOpIntoPhi - Given a binary operator, cast instruction, or select
   // which has a PHI node as operand #0, see if we can fold the instruction