Set debug loc on the IRBuilder instead of instruction

Author: amykhuang

llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp

@@ -1764,6 +1764,7 @@ bool LoopIdiomRecognize::recognizeAndInsertStrLen() {
   }
 
   IRBuilder<> Builder(Preheader->getTerminator());
+  Builder.SetCurrentDebugLocation(CurLoop->getStartLoc());
   SCEVExpander Expander(*SE, Preheader->getModule()->getDataLayout(),
                         "strlen_idiom");
   Value *MaterialzedBase = Expander.expandCodeFor(
@@ -1778,9 +1779,6 @@ bool LoopIdiomRecognize::recognizeAndInsertStrLen() {
   }
   assert(StrLenFunc && "Failed to emit strlen function.");
 
-  // Set debug location to the start of the loop.
-  cast<Instruction>(StrLenFunc)->setDebugLoc(CurLoop->getStartLoc());
-
   const SCEV *StrlenEv = SE->getSCEV(StrLenFunc);
   SmallVector<PHINode *, 4> Cleanup;
   for (PHINode &PN : LoopExitBB->phis()) {