Pass EphValues by const-ref as it is not modified in the callee

Patch by Aditya Kumar.

Differential Revision: https://reviews.llvm.org/D22967

llvm-svn: 277634
diff --git a/llvm/lib/Analysis/CodeMetrics.cpp b/llvm/lib/Analysis/CodeMetrics.cpp
index ed83704..576dca4 100644
--- a/llvm/lib/Analysis/CodeMetrics.cpp
+++ b/llvm/lib/Analysis/CodeMetrics.cpp
@@ -104,7 +104,7 @@
 /// block.
 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
                                     const TargetTransformInfo &TTI,
-                                    SmallPtrSetImpl<const Value*> &EphValues) {
+                                    const SmallPtrSetImpl<const Value*> &EphValues) {
   ++NumBlocks;
   unsigned NumInstsBeforeThisBB = NumInsts;
   for (const Instruction &I : *BB) {