[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 {};
+  const Module &M = *getParent();
+
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teresajohnson wrote:

nit remove blank line between these

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