[SCEVExp] Remove special-case handling umul_with_overflow by 1 (NFCI).

b50ad94 added umul_with_overflow simplifications to
InstSimplifyFolder (used by SCEVExpander) and 9b1b937 added
dead instruction cleanup to SCEVExpander.

Remove special handling of umul by 1, handled automatically due to the
changes above.

Author: fhahn

llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp

@@ -2222,20 +2222,11 @@ Value *SCEVExpander::generateOverflowCheck(const SCEVAddRecExpr *AR,
     // Get the backedge taken count and truncate or extended to the AR type.
     Value *TruncTripCount = Builder.CreateZExtOrTrunc(TripCountVal, Ty);
 
-    Value *MulV, *OfMul;
-    if (Step->isOne()) {
-      // Special-case Step of one. Potentially-costly `umul_with_overflow` isn't
-      // needed, there is never an overflow, so to avoid artificially inflating
-      // the cost of the check, directly emit the optimized IR.
-      MulV = TruncTripCount;
-      OfMul = ConstantInt::getFalse(MulV->getContext());
-    } else {
-      CallInst *Mul = Builder.CreateIntrinsic(Intrinsic::umul_with_overflow, Ty,
-                                              {AbsStep, TruncTripCount},
-                                              /*FMFSource=*/nullptr, "mul");
-      MulV = Builder.CreateExtractValue(Mul, 0, "mul.result");
-      OfMul = Builder.CreateExtractValue(Mul, 1, "mul.overflow");
-    }
+    CallInst *Mul = Builder.CreateIntrinsic(Intrinsic::umul_with_overflow, Ty,
+                                            {AbsStep, TruncTripCount},
+                                            /*FMFSource=*/nullptr, "mul");
+    Value *MulV = Builder.CreateExtractValue(Mul, 0, "mul.result");
+    Value *OfMul = Builder.CreateExtractValue(Mul, 1, "mul.overflow");
 
     Value *Add = nullptr, *Sub = nullptr;
     bool NeedPosCheck = !SE.isKnownNegative(Step);