[clang] [llvm] Compute GUIDs once and store in metadata (PR #184065)

[Teresa Johnson via cfe-commits]

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@@ -81,6 +81,67 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
   return MD5Hash(GlobalIdentifier);
 }
 
+void GlobalValue::assignGUID() {
+  if (getGUIDMetadata() != nullptr)
+    return;
+
+  const GUID G =
+      GlobalValue::getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+  setMetadata(
+      LLVMContext::MD_unique_id,
+      MDNode::get(getContext(), {ConstantAsMetadata::get(ConstantInt::get(
+                                    Type::getInt64Ty(getContext()), G))}));
+}
+
+GlobalValue::GUID GlobalValue::getGUID() const {
+  auto MaybeGUID = getGUIDIfAssigned();
+  assert(MaybeGUID.has_value() &&
+         "GUID was not assigned before calling GetGUID()");
+  return *MaybeGUID;
+}
+
+GlobalValue::GUID GlobalValue::getGUIDOrFallback() const {
+  if (auto MaybeGUID = getGUIDIfAssigned(); MaybeGUID)
+    return *MaybeGUID;
+  return getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+}
+
+std::optional<GlobalValue::GUID> GlobalValue::getGUIDIfAssigned() const {
+  // First check the metadata.
+  auto *MD = getGUIDMetadata();
+  if (MD != nullptr)
+    return cast<ConstantInt>(cast<ConstantAsMetadata>(MD->getOperand(0))
+                                 ->getValue()
+                                 ->stripPointerCasts())
+        ->getZExtValue();
+
+  // Handle a few special cases where we just want to compute it based on the
+  // current properties.
+  // TODO: Maybe we should use a more robust check for intrinsics than just
+  // matching on the name?
+  if (isDeclaration() || isa<GlobalAlias>(this) ||
+      getName().starts_with("llvm.")) {
+    return GlobalValue::getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+  }
+
+  // Otherwise we try to look it up in the module, for cases where we've read
+  // the GUID table but not the metadata. This happens when lazy-loading a
+  // module.
+  if (getParent() == nullptr)
+    return {};
----------------
teresajohnson wrote:

when does this happen (the empty parent case)? If this is during lazy loading, will we have an issue later on once we do load the metadata, which could result in a different GUID in some cases (i.e. when invoking this through getGUIDOrFallback)?

https://github.com/llvm/llvm-project/pull/184065