[LoopIdiomRecognize] Replace more unchecked dyn_casts with cast.

Two of these are immediately dereferenced on the next line. The other two are passed immediately to the IRBuilder constructor which can't handle a nullptr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331500 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopIdiomRecognize.cpp

@@ -1539,7 +1539,7 @@ static CallInst *createCTLZIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
 void LoopIdiomRecognize::transformLoopToCountable(
     BasicBlock *Preheader, Instruction *CntInst, PHINode *CntPhi, Value *InitX,
     const DebugLoc DL, bool ZeroCheck, bool IsCntPhiUsedOutsideLoop) {
-  BranchInst *PreheaderBr = dyn_cast<BranchInst>(Preheader->getTerminator());
+  BranchInst *PreheaderBr = cast<BranchInst>(Preheader->getTerminator());
 
   // Step 1: Insert the CTLZ instruction at the end of the preheader block
   //   Count = BitWidth - CTLZ(InitX);
@@ -1587,7 +1587,7 @@ void LoopIdiomRecognize::transformLoopToCountable(
   //   ...
   //   Br: loop if (Dec != 0)
   BasicBlock *Body = *(CurLoop->block_begin());
-  auto *LbBr = dyn_cast<BranchInst>(Body->getTerminator());
+  auto *LbBr = cast<BranchInst>(Body->getTerminator());
   ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
   Type *Ty = Count->getType();
 
@@ -1624,7 +1624,7 @@ void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
                                                  Instruction *CntInst,
                                                  PHINode *CntPhi, Value *Var) {
   BasicBlock *PreHead = CurLoop->getLoopPreheader();
-  auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
+  auto *PreCondBr = cast<BranchInst>(PreCondBB->getTerminator());
   const DebugLoc DL = CntInst->getDebugLoc();
 
   // Assuming before transformation, the loop is following:
@@ -1695,7 +1695,7 @@ void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
   //     do { cnt++; x &= x-1; t--) } while (t > 0);
   BasicBlock *Body = *(CurLoop->block_begin());
   {
-    auto *LbBr = dyn_cast<BranchInst>(Body->getTerminator());
+    auto *LbBr = cast<BranchInst>(Body->getTerminator());
     ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
     Type *Ty = TripCnt->getType();