[SLP][NFC] Restructure areTwoInsertFromSameBuildVector

[skc7]

Summary

Fix areTwoInsertFromSameBuildVector to check for valid insert index of insertElement instructions.

[ABataev]

LG

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

static bool areTwoInsertFromSameBuildVector(
   // Checks if 2 insertelements are from the same buildvector.
   if (VU->getType() != V->getType())
     return false;
   // Multiple used inserts are separate nodes.
   if (!VU->hasOneUse() && !V->hasOneUse())
     return false;
   auto *IE1 = VU;
   auto *IE2 = V;
-  unsigned Idx1 = *getInsertIndex(IE1);
-  unsigned Idx2 = *getInsertIndex(IE2);
+  Optional<unsigned> Idx1 = getInsertIndex(IE1);
+  Optional<unsigned> Idx2 = getInsertIndex(IE2);
+  if (Idx1 == None || Idx2 == None)
+    return false;
   // Go through the vector operand of insertelement instructions trying to find
   // either VU as the original vector for IE2 or V as the original vector for
   // IE1.
   do {
     if (IE2 == VU)
       return VU->hasOneUse();
     if (IE1 == V)
       return V->hasOneUse();
     if (IE1) {
       if ((IE1 != VU && !IE1->hasOneUse()) ||
-          getInsertIndex(IE1).value_or(Idx2) == Idx2)
+          getInsertIndex(IE1).value_or(*Idx2) == *Idx2)
         IE1 = nullptr;
       else
         IE1 = dyn_cast_or_null<InsertElementInst>(GetBaseOperand(IE1));
     }
     if (IE2) {
       if ((IE2 != V && !IE2->hasOneUse()) ||
-          getInsertIndex(IE2).value_or(Idx1) == Idx1)
+          getInsertIndex(IE2).value_or(*Idx1) == *Idx1)
         IE2 = nullptr;
       else
         IE2 = dyn_cast_or_null<InsertElementInst>(GetBaseOperand(IE2));
     }
   } while (IE1 || IE2);
   return false;
 }