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

[Shilei Tian via llvm-commits]

================
@@ -12767,6 +12768,193 @@ struct AAAddressSpaceCallSiteArgument final : AAAddressSpaceImpl {
 };
 } // namespace
 
+/// ------------------------ No Alias Address Space  ---------------------------
+// This attribute 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());
+
+    unsigned AS = getAssociatedType()->getPointerAddressSpace();
+    if (AS != FlatAS.value()) {
+      removeAS(AS);
+      indicateOptimisticFixpoint();
+    }
+  }
+
+  ChangeStatus updateImpl(Attributor &A) override {
+    unsigned FlatAS = A.getInfoCache().getFlatAddressSpace().value();
+    uint32_t OrigAssumed = getAssumed();
----------------
shiltian wrote:

nit:
```suggestion
    uint32_t OldAssumed = getAssumed();
```

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