Change ConstantFoldInstOperands to take Instruction instead of opcode and type.  NFC.

Summary:
The previous form, taking opcode and type, is moved to an internal
helper and the new form, taking an instruction, is a wrapper around this
helper.

Although this is a slight cleanup on its own, the main motivation is to
refactor the constant folding API to ease migration to opaque pointers.
This will be follow-up work.

Reviewers: eddyb

Subscribers: dblaikie, llvm-commits

Differential Revision: http://reviews.llvm.org/D16383

llvm-svn: 258391
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 3125a2c..8cb1573 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3989,7 +3989,7 @@
                                            COps[1], DL);
   }
 
-  return ConstantFoldInstOperands(I->getOpcode(), I->getType(), COps, DL);
+  return ConstantFoldInstOperands(I, COps, DL);
 }
 
 /// Try to determine the resulting constant values in phi nodes