[SLP] Rework `findBuildAggregate()` from ercursive form to iterative, NFC.

[mkuper]

LGTM with minor comments.

lib/Transforms/Vectorize/SLPVectorizer.cpp

4617 ↗

(On Diff #88915)

Any reason this isn't nullptr? It looks like you never use the initial value.

4628 ↗

(On Diff #88915)

Does the order really matter?
Anyway, if you think it does, I'm fine with this to keep it NFC.

llvm/trunk/lib/Transforms/Vectorize/SLPVectorizer.cpp

 }
 
 /// \brief Like findBuildVector, but looks backwards for construction of aggregate.
 ///
 /// \return true if it matches.
 static bool findBuildAggregate(InsertValueInst *IV,
                                SmallVectorImpl<Value *> &BuildVector,
                                SmallVectorImpl<Value *> &BuildVectorOpds) {
-  if (!IV->hasOneUse())
-    return false;
-  Value *V = IV->getAggregateOperand();
-  if (!isa<UndefValue>(V)) {
-    InsertValueInst *I = dyn_cast<InsertValueInst>(V);
-    if (!I || !findBuildAggregate(I, BuildVector, BuildVectorOpds))
-      return false;
-  }
+  Value *V = IV;
+  do {
     BuildVector.push_back(IV);
     BuildVectorOpds.push_back(IV->getInsertedValueOperand());
+    V = IV->getAggregateOperand();
+    if (isa<UndefValue>(V))
+      break;
+    IV = dyn_cast<InsertValueInst>(V);
+    if (!IV || !IV->hasOneUse())
+      return false;
+  } while (true);
+  std::reverse(BuildVector.begin(), BuildVector.end());
+  std::reverse(BuildVectorOpds.begin(), BuildVectorOpds.end());
   return true;
 }
 
 static bool PhiTypeSorterFunc(Value *V, Value *V2) {
   return V->getType() < V2->getType();
 }
 
 /// \brief Try and get a reduction value from a phi node.