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@orodley orodley commented Mar 31, 2025 •
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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.

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orodley commented Mar 31, 2025 •
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✅ With the latest revision this PR passed the C/C++ code formatter.

@orodley orodley force-pushed the users/orodley/guid-2 branch from 1379952 to dd07516 Compare March 31, 2025 06:47
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Base automatically changed from users/orodley/guid-1 to main April 28, 2025 01:09
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@llvm/pr-subscribers-llvm-ir

@llvm/pr-subscribers-pgo

Author: Owen Rodley (orodley)

Changes

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.

Full diff: https://github.com/llvm/llvm-project/pull/133682.diff

14 Files Affected:

  • (modified) llvm/include/llvm/Analysis/CtxProfAnalysis.h (+5-31)
  • (modified) llvm/include/llvm/IR/FixedMetadataKinds.def (+1)
  • (modified) llvm/include/llvm/IR/GlobalValue.h (+12-3)
  • (added) llvm/include/llvm/Transforms/Utils/AssignGUID.h (+34)
  • (modified) llvm/lib/Analysis/CtxProfAnalysis.cpp (+3-12)
  • (modified) llvm/lib/IR/Globals.cpp (+40)
  • (modified) llvm/lib/Passes/PassBuilder.cpp (+1)
  • (modified) llvm/lib/Passes/PassBuilderPipelines.cpp (+7-2)
  • (modified) llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp (+1-1)
  • (modified) llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp (+1-2)
  • (added) llvm/lib/Transforms/Utils/AssignGUID.cpp (+34)
  • (modified) llvm/lib/Transforms/Utils/CMakeLists.txt (+1)
  • (modified) llvm/lib/Transforms/Utils/CallPromotionUtils.cpp (+2-3)
  • (modified) llvm/lib/Transforms/Utils/InlineFunction.cpp (+2-2)
diff --git a/llvm/include/llvm/Analysis/CtxProfAnalysis.h b/llvm/include/llvm/Analysis/CtxProfAnalysis.h
index aa582cfef1ad1..17ead3b6b978a 100644
--- a/llvm/include/llvm/Analysis/CtxProfAnalysis.h
+++ b/llvm/include/llvm/Analysis/CtxProfAnalysis.h
@@ -46,9 +46,6 @@ class PGOContextualProfile {
   // we'll need when we maintain the profiles during IPO transformations.
   std::map<GlobalValue::GUID, FunctionInfo> FuncInfo;
 
-  /// Get the GUID of this Function if it's defined in this module.
-  GlobalValue::GUID getDefinedFunctionGUID(const Function &F) const;
-
   // This is meant to be constructed from CtxProfAnalysis, which will also set
   // its state piecemeal.
   PGOContextualProfile() = default;
@@ -67,9 +64,7 @@ class PGOContextualProfile {
 
   bool isInSpecializedModule() const;
 
-  bool isFunctionKnown(const Function &F) const {
-    return getDefinedFunctionGUID(F) != 0;
-  }
+  bool isFunctionKnown(const Function &F) const { return F.getGUID() != 0; }
 
   StringRef getFunctionName(GlobalValue::GUID GUID) const {
     auto It = FuncInfo.find(GUID);
@@ -80,22 +75,22 @@ class PGOContextualProfile {
 
   uint32_t getNumCounters(const Function &F) const {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCounterIndex;
+    return FuncInfo.find(F.getGUID())->second.NextCounterIndex;
   }
 
   uint32_t getNumCallsites(const Function &F) const {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCallsiteIndex;
+    return FuncInfo.find(F.getGUID())->second.NextCallsiteIndex;
   }
 
   uint32_t allocateNextCounterIndex(const Function &F) {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCounterIndex++;
+    return FuncInfo.find(F.getGUID())->second.NextCounterIndex++;
   }
 
   uint32_t allocateNextCallsiteIndex(const Function &F) {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCallsiteIndex++;
+    return FuncInfo.find(F.getGUID())->second.NextCallsiteIndex++;
   }
 
   using ConstVisitor = function_ref<void(const PGOCtxProfContext &)>;
@@ -185,26 +180,5 @@ class ProfileAnnotator {
   ~ProfileAnnotator();
 };
 
-/// Assign a GUID to functions as metadata. GUID calculation takes linkage into
-/// account, which may change especially through and after thinlto. By
-/// pre-computing and assigning as metadata, this mechanism is resilient to such
-/// changes (as well as name changes e.g. suffix ".llvm." additions).
-
-// FIXME(mtrofin): we can generalize this mechanism to calculate a GUID early in
-// the pass pipeline, associate it with any Global Value, and then use it for
-// PGO and ThinLTO.
-// At that point, this should be moved elsewhere.
-class AssignGUIDPass : public PassInfoMixin<AssignGUIDPass> {
-public:
-  explicit AssignGUIDPass() = default;
-
-  /// Assign a GUID *if* one is not already assign, as a function metadata named
-  /// `GUIDMetadataName`.
-  PreservedAnalyses run(Module &M, ModuleAnalysisManager &MAM);
-  static const char *GUIDMetadataName;
-  // This should become GlobalValue::getGUID
-  static uint64_t getGUID(const Function &F);
-};
-
 } // namespace llvm
 #endif // LLVM_ANALYSIS_CTXPROFANALYSIS_H
diff --git a/llvm/include/llvm/IR/FixedMetadataKinds.def b/llvm/include/llvm/IR/FixedMetadataKinds.def
index df572e8791e13..e7e3081271093 100644
--- a/llvm/include/llvm/IR/FixedMetadataKinds.def
+++ b/llvm/include/llvm/IR/FixedMetadataKinds.def
@@ -53,3 +53,4 @@ LLVM_FIXED_MD_KIND(MD_DIAssignID, "DIAssignID", 38)
 LLVM_FIXED_MD_KIND(MD_coro_outside_frame, "coro.outside.frame", 39)
 LLVM_FIXED_MD_KIND(MD_mmra, "mmra", 40)
 LLVM_FIXED_MD_KIND(MD_noalias_addrspace, "noalias.addrspace", 41)
+LLVM_FIXED_MD_KIND(MD_unique_id, "unique_id", 42)
diff --git a/llvm/include/llvm/IR/GlobalValue.h b/llvm/include/llvm/IR/GlobalValue.h
index d9ecbb9f8f936..616e3a08a291d 100644
--- a/llvm/include/llvm/IR/GlobalValue.h
+++ b/llvm/include/llvm/IR/GlobalValue.h
@@ -594,11 +594,20 @@ class GlobalValue : public Constant {
   /// the GUID computation will assume that the global has external linkage.
   static GUID getGUIDAssumingExternalLinkage(StringRef GlobalName);
 
+  /// Assign a GUID to this value based on its current name and linkage.
+  /// This GUID will remain the same even if those change. This method is
+  /// idempotent -- if a GUID has already been assigned, calling it again
+  /// will do nothing.
+  ///
+  /// Users don't need to call this method. They are assigned in batch by a
+  /// dedicated pass. The pass pipeline should be set up such that GUIDs are
+  /// always available when needed. If not, the GUID assignment pass should
+  /// be moved such that they are.
+  void assignGUID();
+
   /// Return a 64-bit global unique ID constructed from global value name
   /// (i.e. returned by getGlobalIdentifier()).
-  GUID getGUID() const {
-    return getGUIDAssumingExternalLinkage(getGlobalIdentifier());
-  }
+  GUID getGUID() const;
 
   /// @name Materialization
   /// Materialization is used to construct functions only as they're needed.
diff --git a/llvm/include/llvm/Transforms/Utils/AssignGUID.h b/llvm/include/llvm/Transforms/Utils/AssignGUID.h
new file mode 100644
index 0000000000000..923a1f92cbb7c
--- /dev/null
+++ b/llvm/include/llvm/Transforms/Utils/AssignGUID.h
@@ -0,0 +1,34 @@
+//===-- AssignGUID.h - Unique identifier assignment pass --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a pass which assigns a a GUID (globally unique identifier)
+// to every GlobalValue in the module, according to its current name, linkage,
+// and originating file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
+#define LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
+
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+class AssignGUIDPass : public PassInfoMixin<AssignGUIDPass> {
+public:
+  AssignGUIDPass() = default;
+
+  PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
+
+  static bool isRequired() { return true; }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
\ No newline at end of file
diff --git a/llvm/lib/Analysis/CtxProfAnalysis.cpp b/llvm/lib/Analysis/CtxProfAnalysis.cpp
index a363bce0570e7..d1e0571545cb3 100644
--- a/llvm/lib/Analysis/CtxProfAnalysis.cpp
+++ b/llvm/lib/Analysis/CtxProfAnalysis.cpp
@@ -48,8 +48,6 @@ static cl::opt<bool> ForceIsInSpecializedModule(
     cl::desc("Treat the given module as-if it were containing the "
              "post-thinlink module containing the root"));
 
-const char *AssignGUIDPass::GUIDMetadataName = "guid";
-
 namespace llvm {
 class ProfileAnnotatorImpl final {
   friend class ProfileAnnotator;
@@ -513,7 +511,7 @@ PGOContextualProfile CtxProfAnalysis::run(Module &M,
   for (const auto &F : M) {
     if (F.isDeclaration())
       continue;
-    auto GUID = AssignGUIDPass::getGUID(F);
+    auto GUID = F.getGUID();
     assert(GUID && "guid not found for defined function");
     const auto &Entry = F.begin();
     uint32_t MaxCounters = 0; // we expect at least a counter.
@@ -547,13 +545,6 @@ PGOContextualProfile CtxProfAnalysis::run(Module &M,
   return Result;
 }
 
-GlobalValue::GUID
-PGOContextualProfile::getDefinedFunctionGUID(const Function &F) const {
-  if (auto It = FuncInfo.find(AssignGUIDPass::getGUID(F)); It != FuncInfo.end())
-    return It->first;
-  return 0;
-}
-
 CtxProfAnalysisPrinterPass::CtxProfAnalysisPrinterPass(raw_ostream &OS)
     : OS(OS), Mode(PrintLevel) {}
 
@@ -669,7 +660,7 @@ bool PGOContextualProfile::isInSpecializedModule() const {
 
 void PGOContextualProfile::update(Visitor V, const Function &F) {
   assert(isFunctionKnown(F));
-  GlobalValue::GUID G = getDefinedFunctionGUID(F);
+  GlobalValue::GUID G = F.getGUID();
   for (auto *Node = FuncInfo.find(G)->second.Index.Next; Node;
        Node = Node->Next)
     V(*reinterpret_cast<PGOCtxProfContext *>(Node));
@@ -680,7 +671,7 @@ void PGOContextualProfile::visit(ConstVisitor V, const Function *F) const {
     return preorderVisit<const PGOCtxProfContext::CallTargetMapTy,
                          const PGOCtxProfContext>(Profiles.Contexts, V);
   assert(isFunctionKnown(*F));
-  GlobalValue::GUID G = getDefinedFunctionGUID(*F);
+  GlobalValue::GUID G = F->getGUID();
   for (const auto *Node = FuncInfo.find(G)->second.Index.Next; Node;
        Node = Node->Next)
     V(*reinterpret_cast<const PGOCtxProfContext *>(Node));
diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index 7b799c70a3318..af52c5304d6c6 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/llvm/lib/IR/Globals.cpp
@@ -78,6 +78,46 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
   return MD5Hash(GlobalIdentifier);
 }
 
+void GlobalValue::assignGUID() {
+  if (isDeclaration()) {
+    // Declarations don't get an assigned GUID. Their definition is in another
+    // module, and it may have been promoted from local to external linkage
+    // during LTO. Because of this, we can only determine their GUID once the
+    // definition is available.
+    return;
+  }
+  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 (isa<GlobalAlias>(this)) {
+    return GlobalValue::getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+  }
+
+  if (isDeclaration()) {
+    // Declarations don't get an assigned GUID. Their definition is in another
+    // module, and it may have been promoted from local to external linkage
+    // during LTO. Because of this, we can only determine their GUID once the
+    // definition is available.
+    return 0;
+  }
+
+  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)                                              \
diff --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
index e7057d9a6b625..50651b9f8bf18 100644
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -334,6 +334,7 @@
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
+#include "llvm/Transforms/Utils/AssignGUID.h"
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/BreakCriticalEdges.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index f172271be09ab..35e2bd5d76f26 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -130,6 +130,7 @@
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
+#include "llvm/Transforms/Utils/AssignGUID.h"
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
 #include "llvm/Transforms/Utils/CountVisits.h"
@@ -791,6 +792,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
 void PassBuilder::addRequiredLTOPreLinkPasses(ModulePassManager &MPM) {
   MPM.addPass(CanonicalizeAliasesPass());
   MPM.addPass(NameAnonGlobalPass());
+  MPM.addPass(AssignGUIDPass());
 }
 
 void PassBuilder::addPreInlinerPasses(ModulePassManager &MPM,
@@ -1076,6 +1078,11 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
 
   ModulePassManager MPM;
 
+  if (Phase != ThinOrFullLTOPhase::ThinLTOPostLink) {
+    MPM.addPass(NameAnonGlobalPass());
+    MPM.addPass(AssignGUIDPass());
+  }
+
   // Place pseudo probe instrumentation as the first pass of the pipeline to
   // minimize the impact of optimization changes.
   if (PGOOpt && PGOOpt->PseudoProbeForProfiling &&
@@ -1239,8 +1246,6 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
     // In pre-link, we just want the instrumented IR. We use the contextual
     // profile in the post-thinlink phase.
     // The instrumentation will be removed in post-thinlink after IPO.
-    // FIXME(mtrofin): move AssignGUIDPass if there is agreement to use this
-    // mechanism for GUIDs.
     MPM.addPass(AssignGUIDPass());
     if (IsCtxProfUse) {
       MPM.addPass(PGOCtxProfFlatteningPass(/*IsPreThinlink=*/true));
diff --git a/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp b/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
index e47c9ab75ffe1..757e65d4382fd 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
@@ -181,7 +181,7 @@ PreservedAnalyses PGOCtxProfFlatteningPass::run(Module &M,
            "Function has unreacheable basic blocks. The expectation was that "
            "DCE was run before.");
 
-    auto It = FlattenedProfile.find(AssignGUIDPass::getGUID(F));
+    auto It = FlattenedProfile.find(F.getGUID());
     // If this function didn't appear in the contextual profile, it's cold.
     if (It == FlattenedProfile.end())
       clearColdFunctionProfile(F);
diff --git a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
index d741695d4e53c..142db9179a46e 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
@@ -280,8 +280,7 @@ bool CtxInstrumentationLowerer::lowerFunction(Function &F) {
       assert(Mark->getIndex()->isZero());
 
       IRBuilder<> Builder(Mark);
-      Guid = Builder.getInt64(
-          AssignGUIDPass::getGUID(cast<Function>(*Mark->getNameValue())));
+      Guid = Builder.getInt64(cast<Function>(*Mark->getNameValue()).getGUID());
       // The type of the context of this function is now knowable since we have
       // NumCallsites and NumCounters. We delcare it here because it's more
       // convenient - we have the Builder.
diff --git a/llvm/lib/Transforms/Utils/AssignGUID.cpp b/llvm/lib/Transforms/Utils/AssignGUID.cpp
new file mode 100644
index 0000000000000..8c33ff4b63e91
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/AssignGUID.cpp
@@ -0,0 +1,34 @@
+//===-- AssignGUID.cpp - Unique identifier assignment pass ------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a pass which assigns a a GUID (globally unique identifier)
+// to every GlobalValue in the module, according to its current name, linkage,
+// and originating file.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/AssignGUID.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+PreservedAnalyses AssignGUIDPass::run(Module &M, ModuleAnalysisManager &AM) {
+  for (auto &GV : M.globals()) {
+    if (GV.isDeclaration())
+      continue;
+    GV.assignGUID();
+    dbgs() << "[Added GUID to GV:] " << GV.getName() << "\n";
+  }
+  for (auto &F : M.functions()) {
+    if (F.isDeclaration())
+      continue;
+    F.assignGUID();
+    dbgs() << "[Added GUID to F:] " << F.getName() << "\n";
+  }
+  return PreservedAnalyses::none();
+}
\ No newline at end of file
diff --git a/llvm/lib/Transforms/Utils/CMakeLists.txt b/llvm/lib/Transforms/Utils/CMakeLists.txt
index 78cad0d253be8..9de8ce03ad31f 100644
--- a/llvm/lib/Transforms/Utils/CMakeLists.txt
+++ b/llvm/lib/Transforms/Utils/CMakeLists.txt
@@ -2,6 +2,7 @@ add_llvm_component_library(LLVMTransformUtils
   AddDiscriminators.cpp
   AMDGPUEmitPrintf.cpp
   ASanStackFrameLayout.cpp
+  AssignGUID.cpp
   AssumeBundleBuilder.cpp
   BasicBlockUtils.cpp
   BreakCriticalEdges.cpp
diff --git a/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp b/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
index f0f9add09bf82..6912338ce5ffd 100644
--- a/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
+++ b/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
@@ -616,11 +616,11 @@ CallBase *llvm::promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
   IndirectBBIns->setIndex(IndirectID);
   IndirectBBIns->insertInto(&IndirectBB, IndirectBB.getFirstInsertionPt());
 
-  const GlobalValue::GUID CalleeGUID = AssignGUIDPass::getGUID(Callee);
+  const GlobalValue::GUID CalleeGUID = Callee.getGUID();
   const uint32_t NewCountersSize = IndirectID + 1;
 
   auto ProfileUpdater = [&](PGOCtxProfContext &Ctx) {
-    assert(Ctx.guid() == AssignGUIDPass::getGUID(Caller));
+    assert(Ctx.guid() == Caller.getGUID());
     assert(NewCountersSize - 2 == Ctx.counters().size());
     // All the ctx-es belonging to a function must have the same size counters.
     Ctx.resizeCounters(NewCountersSize);
@@ -655,7 +655,6 @@ CallBase *llvm::promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
     // times, and the indirect BB, IndirectCount times
     Ctx.counters()[DirectID] = DirectCount;
     Ctx.counters()[IndirectID] = IndirectCount;
-
   };
   CtxProf.update(ProfileUpdater, Caller);
   return &DirectCall;
diff --git a/llvm/lib/Transforms/Utils/InlineFunction.cpp b/llvm/lib/Transforms/Utils/InlineFunction.cpp
index 7a91620af8272..1c68cded7896b 100644
--- a/llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ b/llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -2373,7 +2373,7 @@ llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
   // Get some preliminary data about the callsite before it might get inlined.
   // Inlining shouldn't delete the callee, but it's cleaner (and low-cost) to
   // get this data upfront and rely less on InlineFunction's behavior.
-  const auto CalleeGUID = AssignGUIDPass::getGUID(Callee);
+  const auto CalleeGUID = Callee.getGUID();
   auto *CallsiteIDIns = CtxProfAnalysis::getCallsiteInstrumentation(CB);
   const auto CallsiteID =
       static_cast<uint32_t>(CallsiteIDIns->getIndex()->getZExtValue());
@@ -2398,7 +2398,7 @@ llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
   const uint32_t NewCountersSize = CtxProf.getNumCounters(Caller);
 
   auto Updater = [&](PGOCtxProfContext &Ctx) {
-    assert(Ctx.guid() == AssignGUIDPass::getGUID(Caller));
+    assert(Ctx.guid() == Caller.getGUID());
     const auto &[CalleeCounterMap, CalleeCallsiteMap] = IndicesMaps;
     assert(
         (Ctx.counters().size() +

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llvmbot commented Apr 28, 2025

@llvm/pr-subscribers-llvm-analysis

Author: Owen Rodley (orodley)

Changes

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.

Full diff: https://github.com/llvm/llvm-project/pull/133682.diff

14 Files Affected:

  • (modified) llvm/include/llvm/Analysis/CtxProfAnalysis.h (+5-31)
  • (modified) llvm/include/llvm/IR/FixedMetadataKinds.def (+1)
  • (modified) llvm/include/llvm/IR/GlobalValue.h (+12-3)
  • (added) llvm/include/llvm/Transforms/Utils/AssignGUID.h (+34)
  • (modified) llvm/lib/Analysis/CtxProfAnalysis.cpp (+3-12)
  • (modified) llvm/lib/IR/Globals.cpp (+40)
  • (modified) llvm/lib/Passes/PassBuilder.cpp (+1)
  • (modified) llvm/lib/Passes/PassBuilderPipelines.cpp (+7-2)
  • (modified) llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp (+1-1)
  • (modified) llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp (+1-2)
  • (added) llvm/lib/Transforms/Utils/AssignGUID.cpp (+34)
  • (modified) llvm/lib/Transforms/Utils/CMakeLists.txt (+1)
  • (modified) llvm/lib/Transforms/Utils/CallPromotionUtils.cpp (+2-3)
  • (modified) llvm/lib/Transforms/Utils/InlineFunction.cpp (+2-2)
diff --git a/llvm/include/llvm/Analysis/CtxProfAnalysis.h b/llvm/include/llvm/Analysis/CtxProfAnalysis.h
index aa582cfef1ad1..17ead3b6b978a 100644
--- a/llvm/include/llvm/Analysis/CtxProfAnalysis.h
+++ b/llvm/include/llvm/Analysis/CtxProfAnalysis.h
@@ -46,9 +46,6 @@ class PGOContextualProfile {
   // we'll need when we maintain the profiles during IPO transformations.
   std::map<GlobalValue::GUID, FunctionInfo> FuncInfo;
 
-  /// Get the GUID of this Function if it's defined in this module.
-  GlobalValue::GUID getDefinedFunctionGUID(const Function &F) const;
-
   // This is meant to be constructed from CtxProfAnalysis, which will also set
   // its state piecemeal.
   PGOContextualProfile() = default;
@@ -67,9 +64,7 @@ class PGOContextualProfile {
 
   bool isInSpecializedModule() const;
 
-  bool isFunctionKnown(const Function &F) const {
-    return getDefinedFunctionGUID(F) != 0;
-  }
+  bool isFunctionKnown(const Function &F) const { return F.getGUID() != 0; }
 
   StringRef getFunctionName(GlobalValue::GUID GUID) const {
     auto It = FuncInfo.find(GUID);
@@ -80,22 +75,22 @@ class PGOContextualProfile {
 
   uint32_t getNumCounters(const Function &F) const {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCounterIndex;
+    return FuncInfo.find(F.getGUID())->second.NextCounterIndex;
   }
 
   uint32_t getNumCallsites(const Function &F) const {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCallsiteIndex;
+    return FuncInfo.find(F.getGUID())->second.NextCallsiteIndex;
   }
 
   uint32_t allocateNextCounterIndex(const Function &F) {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCounterIndex++;
+    return FuncInfo.find(F.getGUID())->second.NextCounterIndex++;
   }
 
   uint32_t allocateNextCallsiteIndex(const Function &F) {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCallsiteIndex++;
+    return FuncInfo.find(F.getGUID())->second.NextCallsiteIndex++;
   }
 
   using ConstVisitor = function_ref<void(const PGOCtxProfContext &)>;
@@ -185,26 +180,5 @@ class ProfileAnnotator {
   ~ProfileAnnotator();
 };
 
-/// Assign a GUID to functions as metadata. GUID calculation takes linkage into
-/// account, which may change especially through and after thinlto. By
-/// pre-computing and assigning as metadata, this mechanism is resilient to such
-/// changes (as well as name changes e.g. suffix ".llvm." additions).
-
-// FIXME(mtrofin): we can generalize this mechanism to calculate a GUID early in
-// the pass pipeline, associate it with any Global Value, and then use it for
-// PGO and ThinLTO.
-// At that point, this should be moved elsewhere.
-class AssignGUIDPass : public PassInfoMixin<AssignGUIDPass> {
-public:
-  explicit AssignGUIDPass() = default;
-
-  /// Assign a GUID *if* one is not already assign, as a function metadata named
-  /// `GUIDMetadataName`.
-  PreservedAnalyses run(Module &M, ModuleAnalysisManager &MAM);
-  static const char *GUIDMetadataName;
-  // This should become GlobalValue::getGUID
-  static uint64_t getGUID(const Function &F);
-};
-
 } // namespace llvm
 #endif // LLVM_ANALYSIS_CTXPROFANALYSIS_H
diff --git a/llvm/include/llvm/IR/FixedMetadataKinds.def b/llvm/include/llvm/IR/FixedMetadataKinds.def
index df572e8791e13..e7e3081271093 100644
--- a/llvm/include/llvm/IR/FixedMetadataKinds.def
+++ b/llvm/include/llvm/IR/FixedMetadataKinds.def
@@ -53,3 +53,4 @@ LLVM_FIXED_MD_KIND(MD_DIAssignID, "DIAssignID", 38)
 LLVM_FIXED_MD_KIND(MD_coro_outside_frame, "coro.outside.frame", 39)
 LLVM_FIXED_MD_KIND(MD_mmra, "mmra", 40)
 LLVM_FIXED_MD_KIND(MD_noalias_addrspace, "noalias.addrspace", 41)
+LLVM_FIXED_MD_KIND(MD_unique_id, "unique_id", 42)
diff --git a/llvm/include/llvm/IR/GlobalValue.h b/llvm/include/llvm/IR/GlobalValue.h
index d9ecbb9f8f936..616e3a08a291d 100644
--- a/llvm/include/llvm/IR/GlobalValue.h
+++ b/llvm/include/llvm/IR/GlobalValue.h
@@ -594,11 +594,20 @@ class GlobalValue : public Constant {
   /// the GUID computation will assume that the global has external linkage.
   static GUID getGUIDAssumingExternalLinkage(StringRef GlobalName);
 
+  /// Assign a GUID to this value based on its current name and linkage.
+  /// This GUID will remain the same even if those change. This method is
+  /// idempotent -- if a GUID has already been assigned, calling it again
+  /// will do nothing.
+  ///
+  /// Users don't need to call this method. They are assigned in batch by a
+  /// dedicated pass. The pass pipeline should be set up such that GUIDs are
+  /// always available when needed. If not, the GUID assignment pass should
+  /// be moved such that they are.
+  void assignGUID();
+
   /// Return a 64-bit global unique ID constructed from global value name
   /// (i.e. returned by getGlobalIdentifier()).
-  GUID getGUID() const {
-    return getGUIDAssumingExternalLinkage(getGlobalIdentifier());
-  }
+  GUID getGUID() const;
 
   /// @name Materialization
   /// Materialization is used to construct functions only as they're needed.
diff --git a/llvm/include/llvm/Transforms/Utils/AssignGUID.h b/llvm/include/llvm/Transforms/Utils/AssignGUID.h
new file mode 100644
index 0000000000000..923a1f92cbb7c
--- /dev/null
+++ b/llvm/include/llvm/Transforms/Utils/AssignGUID.h
@@ -0,0 +1,34 @@
+//===-- AssignGUID.h - Unique identifier assignment pass --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a pass which assigns a a GUID (globally unique identifier)
+// to every GlobalValue in the module, according to its current name, linkage,
+// and originating file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
+#define LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
+
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+class AssignGUIDPass : public PassInfoMixin<AssignGUIDPass> {
+public:
+  AssignGUIDPass() = default;
+
+  PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
+
+  static bool isRequired() { return true; }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
\ No newline at end of file
diff --git a/llvm/lib/Analysis/CtxProfAnalysis.cpp b/llvm/lib/Analysis/CtxProfAnalysis.cpp
index a363bce0570e7..d1e0571545cb3 100644
--- a/llvm/lib/Analysis/CtxProfAnalysis.cpp
+++ b/llvm/lib/Analysis/CtxProfAnalysis.cpp
@@ -48,8 +48,6 @@ static cl::opt<bool> ForceIsInSpecializedModule(
     cl::desc("Treat the given module as-if it were containing the "
              "post-thinlink module containing the root"));
 
-const char *AssignGUIDPass::GUIDMetadataName = "guid";
-
 namespace llvm {
 class ProfileAnnotatorImpl final {
   friend class ProfileAnnotator;
@@ -513,7 +511,7 @@ PGOContextualProfile CtxProfAnalysis::run(Module &M,
   for (const auto &F : M) {
     if (F.isDeclaration())
       continue;
-    auto GUID = AssignGUIDPass::getGUID(F);
+    auto GUID = F.getGUID();
     assert(GUID && "guid not found for defined function");
     const auto &Entry = F.begin();
     uint32_t MaxCounters = 0; // we expect at least a counter.
@@ -547,13 +545,6 @@ PGOContextualProfile CtxProfAnalysis::run(Module &M,
   return Result;
 }
 
-GlobalValue::GUID
-PGOContextualProfile::getDefinedFunctionGUID(const Function &F) const {
-  if (auto It = FuncInfo.find(AssignGUIDPass::getGUID(F)); It != FuncInfo.end())
-    return It->first;
-  return 0;
-}
-
 CtxProfAnalysisPrinterPass::CtxProfAnalysisPrinterPass(raw_ostream &OS)
     : OS(OS), Mode(PrintLevel) {}
 
@@ -669,7 +660,7 @@ bool PGOContextualProfile::isInSpecializedModule() const {
 
 void PGOContextualProfile::update(Visitor V, const Function &F) {
   assert(isFunctionKnown(F));
-  GlobalValue::GUID G = getDefinedFunctionGUID(F);
+  GlobalValue::GUID G = F.getGUID();
   for (auto *Node = FuncInfo.find(G)->second.Index.Next; Node;
        Node = Node->Next)
     V(*reinterpret_cast<PGOCtxProfContext *>(Node));
@@ -680,7 +671,7 @@ void PGOContextualProfile::visit(ConstVisitor V, const Function *F) const {
     return preorderVisit<const PGOCtxProfContext::CallTargetMapTy,
                          const PGOCtxProfContext>(Profiles.Contexts, V);
   assert(isFunctionKnown(*F));
-  GlobalValue::GUID G = getDefinedFunctionGUID(*F);
+  GlobalValue::GUID G = F->getGUID();
   for (const auto *Node = FuncInfo.find(G)->second.Index.Next; Node;
        Node = Node->Next)
     V(*reinterpret_cast<const PGOCtxProfContext *>(Node));
diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index 7b799c70a3318..af52c5304d6c6 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/llvm/lib/IR/Globals.cpp
@@ -78,6 +78,46 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
   return MD5Hash(GlobalIdentifier);
 }
 
+void GlobalValue::assignGUID() {
+  if (isDeclaration()) {
+    // Declarations don't get an assigned GUID. Their definition is in another
+    // module, and it may have been promoted from local to external linkage
+    // during LTO. Because of this, we can only determine their GUID once the
+    // definition is available.
+    return;
+  }
+  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 (isa<GlobalAlias>(this)) {
+    return GlobalValue::getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+  }
+
+  if (isDeclaration()) {
+    // Declarations don't get an assigned GUID. Their definition is in another
+    // module, and it may have been promoted from local to external linkage
+    // during LTO. Because of this, we can only determine their GUID once the
+    // definition is available.
+    return 0;
+  }
+
+  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)                                              \
diff --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
index e7057d9a6b625..50651b9f8bf18 100644
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -334,6 +334,7 @@
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
+#include "llvm/Transforms/Utils/AssignGUID.h"
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/BreakCriticalEdges.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index f172271be09ab..35e2bd5d76f26 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -130,6 +130,7 @@
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
+#include "llvm/Transforms/Utils/AssignGUID.h"
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
 #include "llvm/Transforms/Utils/CountVisits.h"
@@ -791,6 +792,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
 void PassBuilder::addRequiredLTOPreLinkPasses(ModulePassManager &MPM) {
   MPM.addPass(CanonicalizeAliasesPass());
   MPM.addPass(NameAnonGlobalPass());
+  MPM.addPass(AssignGUIDPass());
 }
 
 void PassBuilder::addPreInlinerPasses(ModulePassManager &MPM,
@@ -1076,6 +1078,11 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
 
   ModulePassManager MPM;
 
+  if (Phase != ThinOrFullLTOPhase::ThinLTOPostLink) {
+    MPM.addPass(NameAnonGlobalPass());
+    MPM.addPass(AssignGUIDPass());
+  }
+
   // Place pseudo probe instrumentation as the first pass of the pipeline to
   // minimize the impact of optimization changes.
   if (PGOOpt && PGOOpt->PseudoProbeForProfiling &&
@@ -1239,8 +1246,6 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
     // In pre-link, we just want the instrumented IR. We use the contextual
     // profile in the post-thinlink phase.
     // The instrumentation will be removed in post-thinlink after IPO.
-    // FIXME(mtrofin): move AssignGUIDPass if there is agreement to use this
-    // mechanism for GUIDs.
     MPM.addPass(AssignGUIDPass());
     if (IsCtxProfUse) {
       MPM.addPass(PGOCtxProfFlatteningPass(/*IsPreThinlink=*/true));
diff --git a/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp b/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
index e47c9ab75ffe1..757e65d4382fd 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
@@ -181,7 +181,7 @@ PreservedAnalyses PGOCtxProfFlatteningPass::run(Module &M,
            "Function has unreacheable basic blocks. The expectation was that "
            "DCE was run before.");
 
-    auto It = FlattenedProfile.find(AssignGUIDPass::getGUID(F));
+    auto It = FlattenedProfile.find(F.getGUID());
     // If this function didn't appear in the contextual profile, it's cold.
     if (It == FlattenedProfile.end())
       clearColdFunctionProfile(F);
diff --git a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
index d741695d4e53c..142db9179a46e 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
@@ -280,8 +280,7 @@ bool CtxInstrumentationLowerer::lowerFunction(Function &F) {
       assert(Mark->getIndex()->isZero());
 
       IRBuilder<> Builder(Mark);
-      Guid = Builder.getInt64(
-          AssignGUIDPass::getGUID(cast<Function>(*Mark->getNameValue())));
+      Guid = Builder.getInt64(cast<Function>(*Mark->getNameValue()).getGUID());
       // The type of the context of this function is now knowable since we have
       // NumCallsites and NumCounters. We delcare it here because it's more
       // convenient - we have the Builder.
diff --git a/llvm/lib/Transforms/Utils/AssignGUID.cpp b/llvm/lib/Transforms/Utils/AssignGUID.cpp
new file mode 100644
index 0000000000000..8c33ff4b63e91
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/AssignGUID.cpp
@@ -0,0 +1,34 @@
+//===-- AssignGUID.cpp - Unique identifier assignment pass ------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a pass which assigns a a GUID (globally unique identifier)
+// to every GlobalValue in the module, according to its current name, linkage,
+// and originating file.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/AssignGUID.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+PreservedAnalyses AssignGUIDPass::run(Module &M, ModuleAnalysisManager &AM) {
+  for (auto &GV : M.globals()) {
+    if (GV.isDeclaration())
+      continue;
+    GV.assignGUID();
+    dbgs() << "[Added GUID to GV:] " << GV.getName() << "\n";
+  }
+  for (auto &F : M.functions()) {
+    if (F.isDeclaration())
+      continue;
+    F.assignGUID();
+    dbgs() << "[Added GUID to F:] " << F.getName() << "\n";
+  }
+  return PreservedAnalyses::none();
+}
\ No newline at end of file
diff --git a/llvm/lib/Transforms/Utils/CMakeLists.txt b/llvm/lib/Transforms/Utils/CMakeLists.txt
index 78cad0d253be8..9de8ce03ad31f 100644
--- a/llvm/lib/Transforms/Utils/CMakeLists.txt
+++ b/llvm/lib/Transforms/Utils/CMakeLists.txt
@@ -2,6 +2,7 @@ add_llvm_component_library(LLVMTransformUtils
   AddDiscriminators.cpp
   AMDGPUEmitPrintf.cpp
   ASanStackFrameLayout.cpp
+  AssignGUID.cpp
   AssumeBundleBuilder.cpp
   BasicBlockUtils.cpp
   BreakCriticalEdges.cpp
diff --git a/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp b/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
index f0f9add09bf82..6912338ce5ffd 100644
--- a/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
+++ b/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
@@ -616,11 +616,11 @@ CallBase *llvm::promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
   IndirectBBIns->setIndex(IndirectID);
   IndirectBBIns->insertInto(&IndirectBB, IndirectBB.getFirstInsertionPt());
 
-  const GlobalValue::GUID CalleeGUID = AssignGUIDPass::getGUID(Callee);
+  const GlobalValue::GUID CalleeGUID = Callee.getGUID();
   const uint32_t NewCountersSize = IndirectID + 1;
 
   auto ProfileUpdater = [&](PGOCtxProfContext &Ctx) {
-    assert(Ctx.guid() == AssignGUIDPass::getGUID(Caller));
+    assert(Ctx.guid() == Caller.getGUID());
     assert(NewCountersSize - 2 == Ctx.counters().size());
     // All the ctx-es belonging to a function must have the same size counters.
     Ctx.resizeCounters(NewCountersSize);
@@ -655,7 +655,6 @@ CallBase *llvm::promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
     // times, and the indirect BB, IndirectCount times
     Ctx.counters()[DirectID] = DirectCount;
     Ctx.counters()[IndirectID] = IndirectCount;
-
   };
   CtxProf.update(ProfileUpdater, Caller);
   return &DirectCall;
diff --git a/llvm/lib/Transforms/Utils/InlineFunction.cpp b/llvm/lib/Transforms/Utils/InlineFunction.cpp
index 7a91620af8272..1c68cded7896b 100644
--- a/llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ b/llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -2373,7 +2373,7 @@ llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
   // Get some preliminary data about the callsite before it might get inlined.
   // Inlining shouldn't delete the callee, but it's cleaner (and low-cost) to
   // get this data upfront and rely less on InlineFunction's behavior.
-  const auto CalleeGUID = AssignGUIDPass::getGUID(Callee);
+  const auto CalleeGUID = Callee.getGUID();
   auto *CallsiteIDIns = CtxProfAnalysis::getCallsiteInstrumentation(CB);
   const auto CallsiteID =
       static_cast<uint32_t>(CallsiteIDIns->getIndex()->getZExtValue());
@@ -2398,7 +2398,7 @@ llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
   const uint32_t NewCountersSize = CtxProf.getNumCounters(Caller);
 
   auto Updater = [&](PGOCtxProfContext &Ctx) {
-    assert(Ctx.guid() == AssignGUIDPass::getGUID(Caller));
+    assert(Ctx.guid() == Caller.getGUID());
     const auto &[CalleeCounterMap, CalleeCallsiteMap] = IndicesMaps;
     assert(
         (Ctx.counters().size() +

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llvmbot commented Apr 28, 2025

@llvm/pr-subscribers-llvm-transforms

Author: Owen Rodley (orodley)

Changes

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.

Full diff: https://github.com/llvm/llvm-project/pull/133682.diff

14 Files Affected:

  • (modified) llvm/include/llvm/Analysis/CtxProfAnalysis.h (+5-31)
  • (modified) llvm/include/llvm/IR/FixedMetadataKinds.def (+1)
  • (modified) llvm/include/llvm/IR/GlobalValue.h (+12-3)
  • (added) llvm/include/llvm/Transforms/Utils/AssignGUID.h (+34)
  • (modified) llvm/lib/Analysis/CtxProfAnalysis.cpp (+3-12)
  • (modified) llvm/lib/IR/Globals.cpp (+40)
  • (modified) llvm/lib/Passes/PassBuilder.cpp (+1)
  • (modified) llvm/lib/Passes/PassBuilderPipelines.cpp (+7-2)
  • (modified) llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp (+1-1)
  • (modified) llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp (+1-2)
  • (added) llvm/lib/Transforms/Utils/AssignGUID.cpp (+34)
  • (modified) llvm/lib/Transforms/Utils/CMakeLists.txt (+1)
  • (modified) llvm/lib/Transforms/Utils/CallPromotionUtils.cpp (+2-3)
  • (modified) llvm/lib/Transforms/Utils/InlineFunction.cpp (+2-2)
diff --git a/llvm/include/llvm/Analysis/CtxProfAnalysis.h b/llvm/include/llvm/Analysis/CtxProfAnalysis.h
index aa582cfef1ad1..17ead3b6b978a 100644
--- a/llvm/include/llvm/Analysis/CtxProfAnalysis.h
+++ b/llvm/include/llvm/Analysis/CtxProfAnalysis.h
@@ -46,9 +46,6 @@ class PGOContextualProfile {
   // we'll need when we maintain the profiles during IPO transformations.
   std::map<GlobalValue::GUID, FunctionInfo> FuncInfo;
 
-  /// Get the GUID of this Function if it's defined in this module.
-  GlobalValue::GUID getDefinedFunctionGUID(const Function &F) const;
-
   // This is meant to be constructed from CtxProfAnalysis, which will also set
   // its state piecemeal.
   PGOContextualProfile() = default;
@@ -67,9 +64,7 @@ class PGOContextualProfile {
 
   bool isInSpecializedModule() const;
 
-  bool isFunctionKnown(const Function &F) const {
-    return getDefinedFunctionGUID(F) != 0;
-  }
+  bool isFunctionKnown(const Function &F) const { return F.getGUID() != 0; }
 
   StringRef getFunctionName(GlobalValue::GUID GUID) const {
     auto It = FuncInfo.find(GUID);
@@ -80,22 +75,22 @@ class PGOContextualProfile {
 
   uint32_t getNumCounters(const Function &F) const {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCounterIndex;
+    return FuncInfo.find(F.getGUID())->second.NextCounterIndex;
   }
 
   uint32_t getNumCallsites(const Function &F) const {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCallsiteIndex;
+    return FuncInfo.find(F.getGUID())->second.NextCallsiteIndex;
   }
 
   uint32_t allocateNextCounterIndex(const Function &F) {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCounterIndex++;
+    return FuncInfo.find(F.getGUID())->second.NextCounterIndex++;
   }
 
   uint32_t allocateNextCallsiteIndex(const Function &F) {
     assert(isFunctionKnown(F));
-    return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCallsiteIndex++;
+    return FuncInfo.find(F.getGUID())->second.NextCallsiteIndex++;
   }
 
   using ConstVisitor = function_ref<void(const PGOCtxProfContext &)>;
@@ -185,26 +180,5 @@ class ProfileAnnotator {
   ~ProfileAnnotator();
 };
 
-/// Assign a GUID to functions as metadata. GUID calculation takes linkage into
-/// account, which may change especially through and after thinlto. By
-/// pre-computing and assigning as metadata, this mechanism is resilient to such
-/// changes (as well as name changes e.g. suffix ".llvm." additions).
-
-// FIXME(mtrofin): we can generalize this mechanism to calculate a GUID early in
-// the pass pipeline, associate it with any Global Value, and then use it for
-// PGO and ThinLTO.
-// At that point, this should be moved elsewhere.
-class AssignGUIDPass : public PassInfoMixin<AssignGUIDPass> {
-public:
-  explicit AssignGUIDPass() = default;
-
-  /// Assign a GUID *if* one is not already assign, as a function metadata named
-  /// `GUIDMetadataName`.
-  PreservedAnalyses run(Module &M, ModuleAnalysisManager &MAM);
-  static const char *GUIDMetadataName;
-  // This should become GlobalValue::getGUID
-  static uint64_t getGUID(const Function &F);
-};
-
 } // namespace llvm
 #endif // LLVM_ANALYSIS_CTXPROFANALYSIS_H
diff --git a/llvm/include/llvm/IR/FixedMetadataKinds.def b/llvm/include/llvm/IR/FixedMetadataKinds.def
index df572e8791e13..e7e3081271093 100644
--- a/llvm/include/llvm/IR/FixedMetadataKinds.def
+++ b/llvm/include/llvm/IR/FixedMetadataKinds.def
@@ -53,3 +53,4 @@ LLVM_FIXED_MD_KIND(MD_DIAssignID, "DIAssignID", 38)
 LLVM_FIXED_MD_KIND(MD_coro_outside_frame, "coro.outside.frame", 39)
 LLVM_FIXED_MD_KIND(MD_mmra, "mmra", 40)
 LLVM_FIXED_MD_KIND(MD_noalias_addrspace, "noalias.addrspace", 41)
+LLVM_FIXED_MD_KIND(MD_unique_id, "unique_id", 42)
diff --git a/llvm/include/llvm/IR/GlobalValue.h b/llvm/include/llvm/IR/GlobalValue.h
index d9ecbb9f8f936..616e3a08a291d 100644
--- a/llvm/include/llvm/IR/GlobalValue.h
+++ b/llvm/include/llvm/IR/GlobalValue.h
@@ -594,11 +594,20 @@ class GlobalValue : public Constant {
   /// the GUID computation will assume that the global has external linkage.
   static GUID getGUIDAssumingExternalLinkage(StringRef GlobalName);
 
+  /// Assign a GUID to this value based on its current name and linkage.
+  /// This GUID will remain the same even if those change. This method is
+  /// idempotent -- if a GUID has already been assigned, calling it again
+  /// will do nothing.
+  ///
+  /// Users don't need to call this method. They are assigned in batch by a
+  /// dedicated pass. The pass pipeline should be set up such that GUIDs are
+  /// always available when needed. If not, the GUID assignment pass should
+  /// be moved such that they are.
+  void assignGUID();
+
   /// Return a 64-bit global unique ID constructed from global value name
   /// (i.e. returned by getGlobalIdentifier()).
-  GUID getGUID() const {
-    return getGUIDAssumingExternalLinkage(getGlobalIdentifier());
-  }
+  GUID getGUID() const;
 
   /// @name Materialization
   /// Materialization is used to construct functions only as they're needed.
diff --git a/llvm/include/llvm/Transforms/Utils/AssignGUID.h b/llvm/include/llvm/Transforms/Utils/AssignGUID.h
new file mode 100644
index 0000000000000..923a1f92cbb7c
--- /dev/null
+++ b/llvm/include/llvm/Transforms/Utils/AssignGUID.h
@@ -0,0 +1,34 @@
+//===-- AssignGUID.h - Unique identifier assignment pass --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a pass which assigns a a GUID (globally unique identifier)
+// to every GlobalValue in the module, according to its current name, linkage,
+// and originating file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
+#define LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
+
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+class AssignGUIDPass : public PassInfoMixin<AssignGUIDPass> {
+public:
+  AssignGUIDPass() = default;
+
+  PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
+
+  static bool isRequired() { return true; }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_ASSIGNGUID_H
\ No newline at end of file
diff --git a/llvm/lib/Analysis/CtxProfAnalysis.cpp b/llvm/lib/Analysis/CtxProfAnalysis.cpp
index a363bce0570e7..d1e0571545cb3 100644
--- a/llvm/lib/Analysis/CtxProfAnalysis.cpp
+++ b/llvm/lib/Analysis/CtxProfAnalysis.cpp
@@ -48,8 +48,6 @@ static cl::opt<bool> ForceIsInSpecializedModule(
     cl::desc("Treat the given module as-if it were containing the "
              "post-thinlink module containing the root"));
 
-const char *AssignGUIDPass::GUIDMetadataName = "guid";
-
 namespace llvm {
 class ProfileAnnotatorImpl final {
   friend class ProfileAnnotator;
@@ -513,7 +511,7 @@ PGOContextualProfile CtxProfAnalysis::run(Module &M,
   for (const auto &F : M) {
     if (F.isDeclaration())
       continue;
-    auto GUID = AssignGUIDPass::getGUID(F);
+    auto GUID = F.getGUID();
     assert(GUID && "guid not found for defined function");
     const auto &Entry = F.begin();
     uint32_t MaxCounters = 0; // we expect at least a counter.
@@ -547,13 +545,6 @@ PGOContextualProfile CtxProfAnalysis::run(Module &M,
   return Result;
 }
 
-GlobalValue::GUID
-PGOContextualProfile::getDefinedFunctionGUID(const Function &F) const {
-  if (auto It = FuncInfo.find(AssignGUIDPass::getGUID(F)); It != FuncInfo.end())
-    return It->first;
-  return 0;
-}
-
 CtxProfAnalysisPrinterPass::CtxProfAnalysisPrinterPass(raw_ostream &OS)
     : OS(OS), Mode(PrintLevel) {}
 
@@ -669,7 +660,7 @@ bool PGOContextualProfile::isInSpecializedModule() const {
 
 void PGOContextualProfile::update(Visitor V, const Function &F) {
   assert(isFunctionKnown(F));
-  GlobalValue::GUID G = getDefinedFunctionGUID(F);
+  GlobalValue::GUID G = F.getGUID();
   for (auto *Node = FuncInfo.find(G)->second.Index.Next; Node;
        Node = Node->Next)
     V(*reinterpret_cast<PGOCtxProfContext *>(Node));
@@ -680,7 +671,7 @@ void PGOContextualProfile::visit(ConstVisitor V, const Function *F) const {
     return preorderVisit<const PGOCtxProfContext::CallTargetMapTy,
                          const PGOCtxProfContext>(Profiles.Contexts, V);
   assert(isFunctionKnown(*F));
-  GlobalValue::GUID G = getDefinedFunctionGUID(*F);
+  GlobalValue::GUID G = F->getGUID();
   for (const auto *Node = FuncInfo.find(G)->second.Index.Next; Node;
        Node = Node->Next)
     V(*reinterpret_cast<const PGOCtxProfContext *>(Node));
diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index 7b799c70a3318..af52c5304d6c6 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/llvm/lib/IR/Globals.cpp
@@ -78,6 +78,46 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
   return MD5Hash(GlobalIdentifier);
 }
 
+void GlobalValue::assignGUID() {
+  if (isDeclaration()) {
+    // Declarations don't get an assigned GUID. Their definition is in another
+    // module, and it may have been promoted from local to external linkage
+    // during LTO. Because of this, we can only determine their GUID once the
+    // definition is available.
+    return;
+  }
+  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 (isa<GlobalAlias>(this)) {
+    return GlobalValue::getGUIDAssumingExternalLinkage(getGlobalIdentifier());
+  }
+
+  if (isDeclaration()) {
+    // Declarations don't get an assigned GUID. Their definition is in another
+    // module, and it may have been promoted from local to external linkage
+    // during LTO. Because of this, we can only determine their GUID once the
+    // definition is available.
+    return 0;
+  }
+
+  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)                                              \
diff --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
index e7057d9a6b625..50651b9f8bf18 100644
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -334,6 +334,7 @@
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
+#include "llvm/Transforms/Utils/AssignGUID.h"
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/BreakCriticalEdges.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index f172271be09ab..35e2bd5d76f26 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -130,6 +130,7 @@
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Scalar/WarnMissedTransforms.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
+#include "llvm/Transforms/Utils/AssignGUID.h"
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
 #include "llvm/Transforms/Utils/CountVisits.h"
@@ -791,6 +792,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
 void PassBuilder::addRequiredLTOPreLinkPasses(ModulePassManager &MPM) {
   MPM.addPass(CanonicalizeAliasesPass());
   MPM.addPass(NameAnonGlobalPass());
+  MPM.addPass(AssignGUIDPass());
 }
 
 void PassBuilder::addPreInlinerPasses(ModulePassManager &MPM,
@@ -1076,6 +1078,11 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
 
   ModulePassManager MPM;
 
+  if (Phase != ThinOrFullLTOPhase::ThinLTOPostLink) {
+    MPM.addPass(NameAnonGlobalPass());
+    MPM.addPass(AssignGUIDPass());
+  }
+
   // Place pseudo probe instrumentation as the first pass of the pipeline to
   // minimize the impact of optimization changes.
   if (PGOOpt && PGOOpt->PseudoProbeForProfiling &&
@@ -1239,8 +1246,6 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
     // In pre-link, we just want the instrumented IR. We use the contextual
     // profile in the post-thinlink phase.
     // The instrumentation will be removed in post-thinlink after IPO.
-    // FIXME(mtrofin): move AssignGUIDPass if there is agreement to use this
-    // mechanism for GUIDs.
     MPM.addPass(AssignGUIDPass());
     if (IsCtxProfUse) {
       MPM.addPass(PGOCtxProfFlatteningPass(/*IsPreThinlink=*/true));
diff --git a/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp b/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
index e47c9ab75ffe1..757e65d4382fd 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp
@@ -181,7 +181,7 @@ PreservedAnalyses PGOCtxProfFlatteningPass::run(Module &M,
            "Function has unreacheable basic blocks. The expectation was that "
            "DCE was run before.");
 
-    auto It = FlattenedProfile.find(AssignGUIDPass::getGUID(F));
+    auto It = FlattenedProfile.find(F.getGUID());
     // If this function didn't appear in the contextual profile, it's cold.
     if (It == FlattenedProfile.end())
       clearColdFunctionProfile(F);
diff --git a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
index d741695d4e53c..142db9179a46e 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
@@ -280,8 +280,7 @@ bool CtxInstrumentationLowerer::lowerFunction(Function &F) {
       assert(Mark->getIndex()->isZero());
 
       IRBuilder<> Builder(Mark);
-      Guid = Builder.getInt64(
-          AssignGUIDPass::getGUID(cast<Function>(*Mark->getNameValue())));
+      Guid = Builder.getInt64(cast<Function>(*Mark->getNameValue()).getGUID());
       // The type of the context of this function is now knowable since we have
       // NumCallsites and NumCounters. We delcare it here because it's more
       // convenient - we have the Builder.
diff --git a/llvm/lib/Transforms/Utils/AssignGUID.cpp b/llvm/lib/Transforms/Utils/AssignGUID.cpp
new file mode 100644
index 0000000000000..8c33ff4b63e91
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/AssignGUID.cpp
@@ -0,0 +1,34 @@
+//===-- AssignGUID.cpp - Unique identifier assignment pass ------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a pass which assigns a a GUID (globally unique identifier)
+// to every GlobalValue in the module, according to its current name, linkage,
+// and originating file.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/AssignGUID.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+PreservedAnalyses AssignGUIDPass::run(Module &M, ModuleAnalysisManager &AM) {
+  for (auto &GV : M.globals()) {
+    if (GV.isDeclaration())
+      continue;
+    GV.assignGUID();
+    dbgs() << "[Added GUID to GV:] " << GV.getName() << "\n";
+  }
+  for (auto &F : M.functions()) {
+    if (F.isDeclaration())
+      continue;
+    F.assignGUID();
+    dbgs() << "[Added GUID to F:] " << F.getName() << "\n";
+  }
+  return PreservedAnalyses::none();
+}
\ No newline at end of file
diff --git a/llvm/lib/Transforms/Utils/CMakeLists.txt b/llvm/lib/Transforms/Utils/CMakeLists.txt
index 78cad0d253be8..9de8ce03ad31f 100644
--- a/llvm/lib/Transforms/Utils/CMakeLists.txt
+++ b/llvm/lib/Transforms/Utils/CMakeLists.txt
@@ -2,6 +2,7 @@ add_llvm_component_library(LLVMTransformUtils
   AddDiscriminators.cpp
   AMDGPUEmitPrintf.cpp
   ASanStackFrameLayout.cpp
+  AssignGUID.cpp
   AssumeBundleBuilder.cpp
   BasicBlockUtils.cpp
   BreakCriticalEdges.cpp
diff --git a/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp b/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
index f0f9add09bf82..6912338ce5ffd 100644
--- a/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
+++ b/llvm/lib/Transforms/Utils/CallPromotionUtils.cpp
@@ -616,11 +616,11 @@ CallBase *llvm::promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
   IndirectBBIns->setIndex(IndirectID);
   IndirectBBIns->insertInto(&IndirectBB, IndirectBB.getFirstInsertionPt());
 
-  const GlobalValue::GUID CalleeGUID = AssignGUIDPass::getGUID(Callee);
+  const GlobalValue::GUID CalleeGUID = Callee.getGUID();
   const uint32_t NewCountersSize = IndirectID + 1;
 
   auto ProfileUpdater = [&](PGOCtxProfContext &Ctx) {
-    assert(Ctx.guid() == AssignGUIDPass::getGUID(Caller));
+    assert(Ctx.guid() == Caller.getGUID());
     assert(NewCountersSize - 2 == Ctx.counters().size());
     // All the ctx-es belonging to a function must have the same size counters.
     Ctx.resizeCounters(NewCountersSize);
@@ -655,7 +655,6 @@ CallBase *llvm::promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
     // times, and the indirect BB, IndirectCount times
     Ctx.counters()[DirectID] = DirectCount;
     Ctx.counters()[IndirectID] = IndirectCount;
-
   };
   CtxProf.update(ProfileUpdater, Caller);
   return &DirectCall;
diff --git a/llvm/lib/Transforms/Utils/InlineFunction.cpp b/llvm/lib/Transforms/Utils/InlineFunction.cpp
index 7a91620af8272..1c68cded7896b 100644
--- a/llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ b/llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -2373,7 +2373,7 @@ llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
   // Get some preliminary data about the callsite before it might get inlined.
   // Inlining shouldn't delete the callee, but it's cleaner (and low-cost) to
   // get this data upfront and rely less on InlineFunction's behavior.
-  const auto CalleeGUID = AssignGUIDPass::getGUID(Callee);
+  const auto CalleeGUID = Callee.getGUID();
   auto *CallsiteIDIns = CtxProfAnalysis::getCallsiteInstrumentation(CB);
   const auto CallsiteID =
       static_cast<uint32_t>(CallsiteIDIns->getIndex()->getZExtValue());
@@ -2398,7 +2398,7 @@ llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
   const uint32_t NewCountersSize = CtxProf.getNumCounters(Caller);
 
   auto Updater = [&](PGOCtxProfContext &Ctx) {
-    assert(Ctx.guid() == AssignGUIDPass::getGUID(Caller));
+    assert(Ctx.guid() == Caller.getGUID());
     const auto &[CalleeCounterMap, CalleeCallsiteMap] = IndicesMaps;
     assert(
         (Ctx.counters().size() +

mtrofin
mtrofin reviewed Apr 28, 2025
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llvm/lib/IR/Globals.cpp
@@ -78,6 +78,46 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
return MD5Hash(GlobalIdentifier);
}

void GlobalValue::assignGUID() {
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does this need to be on GlobalValue? It can just be a detail of the implementation of AssignGUIDPass, and then there's no confusion on the user side about whether it's something they should call or not.

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getMetadata is protected, so it does need to be on GlobalValue

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Looks like setMetadata is as well.

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I wonder if it would be better to make AssignGUIDPass::run a friend so that other users cannot access this functionality.

llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -791,6 +792,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
void PassBuilder::addRequiredLTOPreLinkPasses(ModulePassManager &MPM) {
MPM.addPass(CanonicalizeAliasesPass());
MPM.addPass(NameAnonGlobalPass());
MPM.addPass(AssignGUIDPass());
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this should be added as early as possible, so that (for example) PGO passes can use it. CtxProf definitely needs the GUID present.

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(after reading further below) it seems like the pass is used to ensure there are GUIDs. Should we call it "EnsureGUIDs" then?

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I think that just running it once as early as necessary is the way to go. I must admit I'm a bit lost amongst all the pass construction methods -- can you recommend the best place to put it?

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I believe buildPerModuleDefaultPipeline should be it.

@orodley
Store GUIDs in metadata
9559e0f 
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.
@orodley orodley force-pushed the users/orodley/guid-2 branch from d4948c1 to 9559e0f Compare May 12, 2025 03:56
@orodley orodley mentioned this pull request May 12, 2025
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teresajohnson
teresajohnson reviewed May 16, 2025
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Sorry for the delay. A few comments/questions below. Also needs tests.

llvm/lib/IR/Globals.cpp
@@ -78,6 +78,46 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
return MD5Hash(GlobalIdentifier);
}

void GlobalValue::assignGUID() {
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Looks like setMetadata is as well.

llvm/include/llvm/IR/GlobalValue.h
GUID getGUID() const {
return getGUIDAssumingExternalLinkage(getGlobalIdentifier());
}
GUID getGUID() const;
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Description needs to be updated

llvm/include/llvm/Analysis/CtxProfAnalysis.h
bool isFunctionKnown(const Function &F) const {
return getDefinedFunctionGUID(F) != 0;
}
bool isFunctionKnown(const Function &F) const { return F.getGUID() != 0; }
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Looks like getGUID will assert if there is no metadata, so will this function work as intended? Looks like most of the uses are themselves in asserts, but there is one non-assert call.

llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -1239,8 +1246,6 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
// In pre-link, we just want the instrumented IR. We use the contextual
// profile in the post-thinlink phase.
// The instrumentation will be removed in post-thinlink after IPO.
// FIXME(mtrofin): move AssignGUIDPass if there is agreement to use this
// mechanism for GUIDs.
MPM.addPass(AssignGUIDPass());
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Can / should it be removed from here?

llvm/lib/IR/Globals.cpp
@@ -78,6 +78,46 @@ GlobalValue::getGUIDAssumingExternalLinkage(StringRef GlobalIdentifier) {
return MD5Hash(GlobalIdentifier);
}

void GlobalValue::assignGUID() {
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I wonder if it would be better to make AssignGUIDPass::run a friend so that other users cannot access this functionality.

llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -1076,6 +1078,11 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,

ModulePassManager MPM;

if (Phase != ThinOrFullLTOPhase::ThinLTOPostLink) {
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You'll also want to do this at O0, where this function isn't called, for the supported case of ThinLTO + O0.

llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -1076,6 +1078,11 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,

ModulePassManager MPM;

if (Phase != ThinOrFullLTOPhase::ThinLTOPostLink) {
MPM.addPass(NameAnonGlobalPass());
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Currently this is invoked at the very end of the pre-LTO pipelines (just before we will build the module summary) via addRequiredLTOPreLinkPasses. If it is going to be done early then it can presumably be removed from there. Is it possible for an anon global to be introduced in between this point and the end of the pre-LTO pipeline where we build the summary?

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@orodley @llvmbot @mtrofin @teresajohnson