[clang] [llvm] [mlir] [polly] [IR] Add alias scope domains with disjoint scopes (PR #218768)

[Bruno De Fraine via cfe-commits]

================
@@ -335,6 +335,67 @@ Metadata *BitcodeReaderMetadataList::resolveTypeArray(Metadata *MaybeTuple) {
   return MDTuple::get(Context, Ops);
 }
 
+/// Rebuild \p Old with \p Ops, keeping its identity: a self reference has to
+/// point at the replacement, and a distinct node must not be uniqued.
+static MDNode *rebuildAliasScopeNode(MDNode *Old,
+                                     SmallVectorImpl<Metadata *> &Ops) {
+  LLVMContext &Context = Old->getContext();
+  if (Ops[0] != Old)
+    return Old->isDistinct() ? MDNode::getDistinct(Context, Ops)
+                             : MDNode::get(Context, Ops);
+
+  Ops[0] = nullptr;
+  MDNode *New = MDNode::getDistinct(Context, Ops);
+  New->replaceOperandWith(0, New);
+  return New;
+}
+
+static MDNode *upgradeAliasScopeDomain(MDNode *Domain,
+                                       DenseMap<MDNode *, MDNode *> &Upgraded) {
+  unsigned NumOperands = Domain->getNumOperands();
+  bool HadDescription = NumOperands == 2;
+  // Already upgraded, or invalid and left to the verifier.
+  if (NumOperands == 0 || NumOperands > 2 ||
+      (HadDescription && mdconst::hasa<ConstantInt>(Domain->getOperand(1))))
+    return Domain;
+
+  if (MDNode *Upgrade = Upgraded.lookup(Domain))
+    return Upgrade;
----------------
brunodf-gf wrote:

Here, you can avoid looking up the same key in `Upgraded` twice, because `Upgraded` is not modified in between. For example (since the value cannot be a null pointer):
```suggestion
  MDNode *&Upgrade = Upgraded[Domain];
  if (Upgrade)
    return Upgrade;
```
Then just assign to `Upgrade` further in the function.

https://github.com/llvm/llvm-project/pull/218768