Store GUIDs in metadatausers/orodley/guid-2

See https://discourse.llvm.org/t/rfc-keep-globalvalue-guids-stable/84801
for context.

This takes the existing AssignGUID pass from CtxProfAnalysis, and runs
it by default, at the appropriate stages of the LTO pipeline. It also
changes GlobalValue::getGUID() to retrieve the GUID from the metadata
instead of computing it.

We don't yet have the supporting downstream changes to make a dedicated
GUID table in bitcode, nor do we use the metadata as part of ThinLTO --
it retains its existing mechanisms of recomputing GUIDs from separately
saved data. That will be changed later.

1 files changed, 28 insertions, 0 deletions

diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index 7b799c7..4a4b5bb 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/llvm/lib/IR/Globals.cpp
@@ -78,6 +78,34 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
   return MD5Hash(GlobalIdentifier);
 }
 
+void GlobalValue::assignGUID() {
+  if (getMetadata(LLVMContext::MD_unique_id) != 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 {
+  if (isDeclaration()) {
+    return GlobalValue::getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+  }
+  if (isa<GlobalAlias>(this)) {
+    return GlobalValue::getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+  }
+
+  auto *MD = getMetadata(LLVMContext::MD_unique_id);
+  assert(MD != nullptr && "GUID was not assigned before calling GetGUID()");
+  return cast<ConstantInt>(cast<ConstantAsMetadata>(MD->getOperand(0))
+                               ->getValue()
+                               ->stripPointerCasts())
+      ->getZExtValue();
+}
+
 void GlobalValue::removeFromParent() {
   switch (getValueID()) {
 #define HANDLE_GLOBAL_VALUE(NAME)                                              \