replace AltIndex with AltOp

Author: HanKuanChen

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -926,9 +926,9 @@ static InstructionsState getSameOpcode(ArrayRef<Value *> VL,
   bool IsCmpOp = isa<CmpInst>(MainOp);
   CmpInst::Predicate BasePred = IsCmpOp ? cast<CmpInst>(MainOp)->getPredicate()
                                         : CmpInst::BAD_ICMP_PREDICATE;
+  Instruction *AltOp = MainOp;
   unsigned Opcode = MainOp->getOpcode();
   unsigned AltOpcode = Opcode;
-  unsigned AltIndex = std::distance(VL.begin(), It);
 
   bool SwappedPredsCompatible = IsCmpOp && [&]() {
     SetVector<unsigned> UniquePreds, UniqueNonSwappedPreds;
@@ -979,7 +979,7 @@ static InstructionsState getSameOpcode(ArrayRef<Value *> VL,
       if (Opcode == AltOpcode && isValidForAlternation(InstOpcode) &&
           isValidForAlternation(Opcode)) {
         AltOpcode = InstOpcode;
-        AltIndex = Cnt;
+        AltOp = I;
         continue;
       }
     } else if (IsCastOp && isa<CastInst>(I)) {
@@ -995,7 +995,7 @@ static InstructionsState getSameOpcode(ArrayRef<Value *> VL,
                  isValidForAlternation(InstOpcode) &&
                  "Cast isn't safe for alternation, logic needs to be updated!");
           AltOpcode = InstOpcode;
-          AltIndex = Cnt;
+          AltOp = I;
           continue;
         }
       }
@@ -1020,15 +1020,15 @@ static InstructionsState getSameOpcode(ArrayRef<Value *> VL,
 
         if (isCmpSameOrSwapped(BaseInst, Inst, TLI))
           continue;
-        auto *AltInst = cast<CmpInst>(VL[AltIndex]);
-        if (AltIndex) {
+        auto *AltInst = cast<CmpInst>(AltOp);
+        if (MainOp != AltOp) {
           if (isCmpSameOrSwapped(AltInst, Inst, TLI))
             continue;
         } else if (BasePred != CurrentPred) {
           assert(
               isValidForAlternation(InstOpcode) &&
               "CmpInst isn't safe for alternation, logic needs to be updated!");
-          AltIndex = Cnt;
+          AltOp = I;
           continue;
         }
         CmpInst::Predicate AltPred = AltInst->getPredicate();
@@ -1082,7 +1082,7 @@ static InstructionsState getSameOpcode(ArrayRef<Value *> VL,
     return InstructionsState::invalid();
   }
 
-  return InstructionsState(MainOp, cast<Instruction>(VL[AltIndex]));
+  return InstructionsState(MainOp, AltOp);
 }
 
 /// \returns true if all of the values in \p VL have the same type or false