[llvm] [MemCpyOpt] Merge memset and skip unrelated clobber in one scan (PR #90350)

[Nikita Popov via llvm-commits]

================
@@ -350,157 +434,148 @@ static void combineAAMetadata(Instruction *ReplInst, Instruction *I) {
   combineMetadata(ReplInst, I, KnownIDs, true);
 }
 
+// Return the byte value of instruction.
+static Value * isCandidateToMergeIntoMemset(Instruction *I, const DataLayout &DL) {
+  if (auto *SI = dyn_cast<StoreInst>(I)) {
+    Value *StoredVal = SI->getValueOperand();
+
+    // Avoid merging nontemporal stores since the resulting
+    // memcpy/memset would not be able to preserve the nontemporal hint.
+    if (SI->getMetadata(LLVMContext::MD_nontemporal))
+      return nullptr;
+    // Don't convert stores of non-integral pointer types to memsets (which
+    // stores integers).
+    if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
+      return nullptr;
+
+    // We can't track ranges involving scalable types.
+    if (DL.getTypeStoreSize(StoredVal->getType()).isScalable())
+      return nullptr;
+
+    return isBytewiseValue(StoredVal, DL);
+  }
+
+  if (auto *MSI = dyn_cast<MemSetInst>(I)) {
+    if (!isa<ConstantInt>(MSI->getLength()))
+      return nullptr;
+
+    return MSI->getValue();
+  }
+
+  return nullptr;
+}
+
+static Value *getWrittenPtr(Instruction *I) {
+  if (auto *SI = dyn_cast<StoreInst>(I))
+    return SI->getPointerOperand();
+  if (auto *MSI = dyn_cast<MemSetInst>(I))
+    return MSI->getDest();
+  static_assert("Only support store and memset");
----------------
nikic wrote:

```suggestion
  llvm_unreachable("Only support store and memset");
```

https://github.com/llvm/llvm-project/pull/90350