[llvm] [VectorCombine] Try to scalarize vector loads feeding bitcast instructions. (PR #164682)

[Florian Hahn via llvm-commits]

================
@@ -1845,49 +1847,42 @@ bool VectorCombine::foldSingleElementStore(Instruction &I) {
   return false;
 }
 
-/// Try to scalarize vector loads feeding extractelement instructions.
-bool VectorCombine::scalarizeLoadExtract(Instruction &I) {
-  if (!TTI.allowVectorElementIndexingUsingGEP())
-    return false;
-
+/// Try to scalarize vector loads feeding extractelement or bitcast
+/// instructions.
+bool VectorCombine::scalarizeLoad(Instruction &I) {
   Value *Ptr;
   if (!match(&I, m_Load(m_Value(Ptr))))
     return false;
 
   auto *LI = cast<LoadInst>(&I);
   auto *VecTy = cast<VectorType>(LI->getType());
-  if (LI->isVolatile() || !DL->typeSizeEqualsStoreSize(VecTy->getScalarType()))
+  if (!VecTy || LI->isVolatile() ||
+      !DL->typeSizeEqualsStoreSize(VecTy->getScalarType()))
     return false;
 
-  InstructionCost OriginalCost =
-      TTI.getMemoryOpCost(Instruction::Load, VecTy, LI->getAlign(),
-                          LI->getPointerAddressSpace(), CostKind);
-  InstructionCost ScalarizedCost = 0;
-
+  // Check what type of users we have and ensure no memory modifications betwwen
+  // the load and its users.
+  bool AllExtracts = true;
+  bool AllBitcasts = true;
   Instruction *LastCheckedInst = LI;
   unsigned NumInstChecked = 0;
-  DenseMap<ExtractElementInst *, ScalarizationResult> NeedFreeze;
-  auto FailureGuard = make_scope_exit([&]() {
-    // If the transform is aborted, discard the ScalarizationResults.
-    for (auto &Pair : NeedFreeze)
-      Pair.second.discard();
-  });
 
-  // Check if all users of the load are extracts with no memory modifications
-  // between the load and the extract. Compute the cost of both the original
-  // code and the scalarized version.
   for (User *U : LI->users()) {
-    auto *UI = dyn_cast<ExtractElementInst>(U);
-    if (!UI || UI->getParent() != LI->getParent())
+    auto *UI = dyn_cast<Instruction>(U);
+    if (!UI || UI->getParent() != LI->getParent() || UI->use_empty())
       return false;
----------------
fhahn wrote:

```suggestion
    if (!UI || UI->getParent() != LI->getParent())
      return false;
```

also checked below, with explanation in comment?

https://github.com/llvm/llvm-project/pull/164682