[InstCombine] add assert in SimplifyDemandedVectorElts and improve readability; NFC

Author: rotateright

llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -1247,28 +1247,31 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
     break;
   }
   case Instruction::ShuffleVector: {
-    ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
-    unsigned LHSVWidth =
-      Shuffle->getOperand(0)->getType()->getVectorNumElements();
-    APInt LeftDemanded(LHSVWidth, 0), RightDemanded(LHSVWidth, 0);
+    auto *Shuffle = cast<ShuffleVectorInst>(I);
+    assert(Shuffle->getOperand(0)->getType() ==
+           Shuffle->getOperand(1)->getType() &&
+           "Expected shuffle operands to have same type");
+    unsigned OpWidth =
+        Shuffle->getOperand(0)->getType()->getVectorNumElements();
+    APInt LeftDemanded(OpWidth, 0), RightDemanded(OpWidth, 0);
     for (unsigned i = 0; i < VWidth; i++) {
       if (DemandedElts[i]) {
         unsigned MaskVal = Shuffle->getMaskValue(i);
         if (MaskVal != -1u) {
-          assert(MaskVal < LHSVWidth * 2 &&
+          assert(MaskVal < OpWidth * 2 &&
                  "shufflevector mask index out of range!");
-          if (MaskVal < LHSVWidth)
+          if (MaskVal < OpWidth)
             LeftDemanded.setBit(MaskVal);
           else
-            RightDemanded.setBit(MaskVal - LHSVWidth);
+            RightDemanded.setBit(MaskVal - OpWidth);
         }
       }
     }
 
-    APInt LHSUndefElts(LHSVWidth, 0);
+    APInt LHSUndefElts(OpWidth, 0);
     simplifyAndSetOp(I, 0, LeftDemanded, LHSUndefElts);
 
-    APInt RHSUndefElts(LHSVWidth, 0);
+    APInt RHSUndefElts(OpWidth, 0);
     simplifyAndSetOp(I, 1, RightDemanded, RHSUndefElts);
 
     bool NewUndefElts = false;
@@ -1283,23 +1286,23 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
       } else if (!DemandedElts[i]) {
         NewUndefElts = true;
         UndefElts.setBit(i);
-      } else if (MaskVal < LHSVWidth) {
+      } else if (MaskVal < OpWidth) {
         if (LHSUndefElts[MaskVal]) {
           NewUndefElts = true;
           UndefElts.setBit(i);
         } else {
-          LHSIdx = LHSIdx == -1u ? i : LHSVWidth;
-          LHSValIdx = LHSValIdx == -1u ? MaskVal : LHSVWidth;
+          LHSIdx = LHSIdx == -1u ? i : OpWidth;
+          LHSValIdx = LHSValIdx == -1u ? MaskVal : OpWidth;
           LHSUniform = LHSUniform && (MaskVal == i);
         }
       } else {
-        if (RHSUndefElts[MaskVal - LHSVWidth]) {
+        if (RHSUndefElts[MaskVal - OpWidth]) {
           NewUndefElts = true;
           UndefElts.setBit(i);
         } else {
-          RHSIdx = RHSIdx == -1u ? i : LHSVWidth;
-          RHSValIdx = RHSValIdx == -1u ? MaskVal - LHSVWidth : LHSVWidth;
-          RHSUniform = RHSUniform && (MaskVal - LHSVWidth == i);
+          RHSIdx = RHSIdx == -1u ? i : OpWidth;
+          RHSValIdx = RHSValIdx == -1u ? MaskVal - OpWidth : OpWidth;
+          RHSUniform = RHSUniform && (MaskVal - OpWidth == i);
         }
       }
     }
@@ -1308,20 +1311,20 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
     // this constant vector to single insertelement instruction.
     // shufflevector V, C, <v1, v2, .., ci, .., vm> ->
     // insertelement V, C[ci], ci-n
-    if (LHSVWidth == Shuffle->getType()->getNumElements()) {
+    if (OpWidth == Shuffle->getType()->getNumElements()) {
       Value *Op = nullptr;
       Constant *Value = nullptr;
       unsigned Idx = -1u;
 
       // Find constant vector with the single element in shuffle (LHS or RHS).
-      if (LHSIdx < LHSVWidth && RHSUniform) {
+      if (LHSIdx < OpWidth && RHSUniform) {
         if (auto *CV = dyn_cast<ConstantVector>(Shuffle->getOperand(0))) {
           Op = Shuffle->getOperand(1);
           Value = CV->getOperand(LHSValIdx);
           Idx = LHSIdx;
         }
       }
-      if (RHSIdx < LHSVWidth && LHSUniform) {
+      if (RHSIdx < OpWidth && LHSUniform) {
         if (auto *CV = dyn_cast<ConstantVector>(Shuffle->getOperand(1))) {
           Op = Shuffle->getOperand(0);
           Value = CV->getOperand(RHSValIdx);