[llvm] Attributor: Infer noalias.addrspace metadata for memory instructions (PR #136553)

[Matt Arsenault via llvm-commits]

================
@@ -12778,6 +12779,191 @@ struct AAAddressSpaceCallSiteArgument final : AAAddressSpaceImpl {
 };
 } // namespace
 
+/// ------------------------ No Alias Address Space  ---------------------------
+// This attrubte assumes flat address space can alias all other address space
+namespace {
+struct AANoAliasAddrSpaceImpl : public AANoAliasAddrSpace {
+  AANoAliasAddrSpaceImpl(const IRPosition &IRP, Attributor &A)
+      : AANoAliasAddrSpace(IRP, A) {}
+
+  void initialize(Attributor &A) override {
+    assert(getAssociatedType()->isPtrOrPtrVectorTy() &&
+           "Associated value is not a pointer");
+
+    resetASRanges(A);
+
+    auto FlatAS = A.getInfoCache().getFlatAddressSpace();
+    if (!FlatAS.has_value()) {
+      indicatePessimisticFixpoint();
+      return;
+    }
+
+    removeAS(FlatAS.value());
----------------
arsenm wrote:

```suggestion
    removeAS(*FlatAS);
```

It's more canonical to use operator bool() and operator* on optional 

https://github.com/llvm/llvm-project/pull/136553