[Scalarizer] Ensure valid VectorSplits for each struct element in visitExtractValueInst (#128538)

Fixes #127739 

The `visitExtractValueInst` is missing a check that was present in
`splitCall` / `visitCallInst`.
This check ensures that each struct element has a VectorSplit, and that
each VectorSplit contains the same number of elements packed per
fragment.

---------

Co-authored-by: Jay Foad <[email protected]>

Author: Icohedron

llvm/lib/Transforms/Scalar/Scalarizer.cpp

@@ -719,13 +719,12 @@ bool ScalarizerVisitor::splitCall(CallInst &CI) {
     for (unsigned I = 1; I < CallType->getNumContainedTypes(); I++) {
       std::optional<VectorSplit> CurrVS =
           getVectorSplit(cast<FixedVectorType>(CallType->getContainedType(I)));
-      // This case does not seem to happen, but it is possible for
-      // VectorSplit.NumPacked >= NumElems. If that happens a VectorSplit
-      // is not returned and we will bailout of handling this call.
-      // The secondary bailout case is if NumPacked does not match.
-      // This can happen if ScalarizeMinBits is not set to the default.
-      // This means with certain ScalarizeMinBits intrinsics like frexp
-      // will only scalarize when the struct elements have the same bitness.
+      // It is possible for VectorSplit.NumPacked >= NumElems. If that happens a
+      // VectorSplit is not returned and we will bailout of handling this call.
+      // The secondary bailout case is if NumPacked does not match. This can
+      // happen if ScalarizeMinBits is not set to the default. This means with
+      // certain ScalarizeMinBits intrinsics like frexp will only scalarize when
+      // the struct elements have the same bitness.
       if (!CurrVS || CurrVS->NumPacked != VS->NumPacked)
         return false;
       if (isVectorIntrinsicWithStructReturnOverloadAtField(ID, I, TTI))
@@ -1083,6 +1082,18 @@ bool ScalarizerVisitor::visitExtractValueInst(ExtractValueInst &EVI) {
   std::optional<VectorSplit> VS = getVectorSplit(VecType);
   if (!VS)
     return false;
+  for (unsigned I = 1; I < OpTy->getNumContainedTypes(); I++) {
+    std::optional<VectorSplit> CurrVS =
+        getVectorSplit(cast<FixedVectorType>(OpTy->getContainedType(I)));
+    // It is possible for VectorSplit.NumPacked >= NumElems. If that happens a
+    // VectorSplit is not returned and we will bailout of handling this call.
+    // The secondary bailout case is if NumPacked does not match. This can
+    // happen if ScalarizeMinBits is not set to the default. This means with
+    // certain ScalarizeMinBits intrinsics like frexp will only scalarize when
+    // the struct elements have the same bitness.
+    if (!CurrVS || CurrVS->NumPacked != VS->NumPacked)
+      return false;
+  }
   IRBuilder<> Builder(&EVI);
   Scatterer Op0 = scatter(&EVI, Op, *VS);
   assert(!EVI.getIndices().empty() && "Make sure an index exists");