[InstCombine] Make foldOpWithConstantIntoOperand take a BinaryOperator instead of a generic Instruction.

It blindly assumes there are two operands so make it explicit.

llvm-svn: 299351
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 88e6542..ab15fd8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -571,7 +571,7 @@
   Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI);
 
   /// This is a convenience wrapper function for the above two functions.
-  Instruction *foldOpWithConstantIntoOperand(Instruction &I);
+  Instruction *foldOpWithConstantIntoOperand(BinaryOperator &I);
 
   /// \brief Try to rotate an operation below a PHI node, using PHI nodes for
   /// its operands.