[llvm] Attributor: Add noalias.addrspace attribute for store and load (PR #136553)

[via llvm-commits]

================
@@ -12784,6 +12785,172 @@ struct AAAddressSpaceCallSiteArgument final : AAAddressSpaceImpl {
 };
 } // namespace
 
+/// ------------------------ No Alias 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");
+
+    if (!A.getInfoCache().getFlatAddressSpace().has_value()) {
+      indicatePessimisticFixpoint();
+      return;
+    }
+
+    unsigned FlatAS = A.getInfoCache().getFlatAddressSpace().value();
+    unsigned AS = getAssociatedType()->getPointerAddressSpace();
+    if (AS != FlatAS) {
+      removeAssumedBits(1 << AS);
+      indicateOptimisticFixpoint();
+    }
+  }
+
+  ChangeStatus updateImpl(Attributor &A) override {
+    unsigned FlatAS = A.getInfoCache().getFlatAddressSpace().value();
+    uint32_t OrigAssumed = getAssumed();
+
+    auto CheckAddressSpace = [&](Value &Obj) {
+      if (isa<UndefValue>(&Obj))
+        return true;
+      // Handle argument in flat address space only has addrspace cast uses
+      if (auto *Arg = dyn_cast<Argument>(&Obj)) {
+        if (Arg->getType()->getPointerAddressSpace() == FlatAS) {
+          for (auto *U : Arg->users()) {
+            auto *ASCI = dyn_cast<AddrSpaceCastInst>(U);
+            if (!ASCI)
+              return false;
+            if (ASCI->getDestAddressSpace() == FlatAS)
+              return false;
+            removeAssumedBits(1 << ASCI->getDestAddressSpace());
+          }
+        }
+      }
+      removeAssumedBits(1 << Obj.getType()->getPointerAddressSpace());
+      return true;
+    };
+
+    auto *AUO = A.getOrCreateAAFor<AAUnderlyingObjects>(getIRPosition(), this,
+                                                        DepClassTy::REQUIRED);
+    if (!AUO->forallUnderlyingObjects(CheckAddressSpace))
+      return indicatePessimisticFixpoint();
+
+    return OrigAssumed == getAssumed() ? ChangeStatus::UNCHANGED
+                                       : ChangeStatus::CHANGED;
+  }
+
+  /// See AbstractAttribute::manifest(...).
+  ChangeStatus manifest(Attributor &A) override {
+    if (!A.getInfoCache().getFlatAddressSpace().has_value())
+      return ChangeStatus::UNCHANGED;
+
+    unsigned FlatAS = A.getInfoCache().getFlatAddressSpace().value();
+    unsigned AS = getAssociatedType()->getPointerAddressSpace();
+    if (AS != FlatAS)
+      return ChangeStatus::UNCHANGED;
----------------
Shoreshen wrote:

Hi @arsenm @shiltian , my understanding is if the associated value it self has a address space that is not flat, then we don't need the attribute since it will not access other address space, like the following example:
```ll
%ptr = addrspacecast ptr %gptr to ptr addrspace(3)
store i32 %val, ptr addrspace(3) %ptr
```

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