Index: include/llvm/Passes/PassBuilder.h
===================================================================
--- include/llvm/Passes/PassBuilder.h
+++ include/llvm/Passes/PassBuilder.h
@@ -71,6 +71,18 @@
     std::vector<PipelineElement> InnerPipeline;
   };
 
+  /// \brief ThinLTO optimization phase.
+  ///
+  /// This enumerates the LLVM ThinLTO optimization phases.
+  enum class ThinLTOPhase {
+    /// No ThinLTO behavior needed.
+    None,
+    // ThinLTO prelink (summary) phase.
+    PreLink,
+    // ThinLTO postlink (backend compile) phase.
+    PostLink
+  };
+
   /// \brief LLVM-provided high-level optimization levels.
   ///
   /// This enumerates the LLVM-provided high-level optimization levels. Each
@@ -214,13 +226,11 @@
   /// require some transformations for semantic reasons, they should explicitly
   /// build them.
   ///
-  /// \p PrepareForThinLTO indicates whether this is invoked in
-  /// PrepareForThinLTO phase. Special handling is needed for sample PGO to
-  /// ensure profile accurate in the backend profile annotation phase.
+  /// \p Phase indicates the current optimization phase.
   FunctionPassManager
   buildFunctionSimplificationPipeline(OptimizationLevel Level,
-                                      bool DebugLogging = false,
-                                      bool PrepareForThinLTO = false);
+                                      ThinLTOPhase Phase,
+                                      bool DebugLogging = false);
 
   /// Construct the core LLVM module canonicalization and simplification
   /// pipeline.
@@ -236,13 +246,11 @@
   /// require some transformations for semantic reasons, they should explicitly
   /// build them.
   ///
-  /// \p PrepareForThinLTO indicates whether this is invoked in
-  /// PrepareForThinLTO phase. Special handling is needed for sample PGO to
-  /// ensure profile accurate in the backend profile annotation phase.
+  /// \p Phase indicates the current optimization phase.
   ModulePassManager
   buildModuleSimplificationPipeline(OptimizationLevel Level,
-                                    bool DebugLogging = false,
-                                    bool PrepareForThinLTO = false);
+                                    ThinLTOPhase Phase,
+                                    bool DebugLogging = false);
 
   /// Construct the core LLVM module optimization pipeline.
   ///
Index: lib/Passes/PassBuilder.cpp
===================================================================
--- lib/Passes/PassBuilder.cpp
+++ lib/Passes/PassBuilder.cpp
@@ -325,8 +325,8 @@
 
 FunctionPassManager
 PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
-                                                 bool DebugLogging,
-                                                 bool PrepareForThinLTO) {
+                                                 ThinLTOPhase Phase,
+                                                 bool DebugLogging) {
   assert(Level != O0 && "Must request optimizations!");
   FunctionPassManager FPM(DebugLogging);
 
@@ -389,10 +389,11 @@
     C(LPM2, Level);
 
   LPM2.addPass(LoopDeletionPass());
-  // Do not enable unrolling in PrepareForThinLTO phase during sample PGO
+  // Do not enable unrolling in PreLinkThinLTO phase during sample PGO
   // because it changes IR to makes profile annotation in back compile
   // inaccurate.
-  if (!PrepareForThinLTO || !PGOOpt || PGOOpt->SampleProfileFile.empty())
+  if (Phase != ThinLTOPhase::PreLink ||
+      !PGOOpt || PGOOpt->SampleProfileFile.empty())
     LPM2.addPass(LoopUnrollPass::createFull(Level));
 
   for (auto &C : LoopOptimizerEndEPCallbacks)
@@ -524,8 +525,8 @@
 
 ModulePassManager
 PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
-                                               bool DebugLogging,
-                                               bool PrepareForThinLTO) {
+                                               ThinLTOPhase Phase,
+                                               bool DebugLogging) {
   ModulePassManager MPM(DebugLogging);
 
   // Do basic inference of function attributes from known properties of system
@@ -581,9 +582,9 @@
       MPM.addPass(SampleProfileLoaderPass(PGOOpt->SampleProfileFile));
 
     // Indirect call promotion that promotes intra-module targes only.
-    // Do not enable it in PrepareForThinLTO phase during sample PGO because
+    // Do not enable it in PreLinkThinLTO phase during sample PGO because
     // it changes IR to makes profile annotation in back compile inaccurate.
-    if ((!PrepareForThinLTO && !PGOOpt->SampleProfileFile.empty())
+    if ((Phase != ThinLTOPhase::PreLink && !PGOOpt->SampleProfileFile.empty())
         || !PGOOpt->ProfileUseFile.empty())
       MPM.addPass(PGOIndirectCallPromotion(
           false, PGOOpt && !PGOOpt->SampleProfileFile.empty()));
@@ -611,10 +612,11 @@
   // Run the inliner first. The theory is that we are walking bottom-up and so
   // the callees have already been fully optimized, and we want to inline them
   // into the callers so that our optimizations can reflect that.
-  // For PrepareForThinLTO pass, we disable hot-caller heuristic for sample PGO
+  // For PreLinkThinLTO pass, we disable hot-caller heuristic for sample PGO
   // because it makes profile annotation in the backend inaccurate.
   InlineParams IP = getInlineParamsFromOptLevel(Level);
-  if (PrepareForThinLTO && PGOOpt && !PGOOpt->SampleProfileFile.empty())
+  if (Phase == ThinLTOPhase::PreLink &&
+      PGOOpt && !PGOOpt->SampleProfileFile.empty())
     IP.HotCallSiteThreshold = 0;
   MainCGPipeline.addPass(InlinerPass(IP));
 
@@ -629,8 +631,7 @@
   // Lastly, add the core function simplification pipeline nested inside the
   // CGSCC walk.
   MainCGPipeline.addPass(createCGSCCToFunctionPassAdaptor(
-      buildFunctionSimplificationPipeline(Level, DebugLogging,
-                                          PrepareForThinLTO)));
+      buildFunctionSimplificationPipeline(Level, Phase, DebugLogging)));
 
   for (auto &C : CGSCCOptimizerLateEPCallbacks)
     C(MainCGPipeline, Level);
@@ -782,8 +783,8 @@
     MPM.addPass(createModuleToFunctionPassAdaptor(AddDiscriminatorsPass()));
 
   // Add the core simplification pipeline.
-  MPM.addPass(buildModuleSimplificationPipeline(Level, DebugLogging,
-                                                /*PrepareForThinLTO=*/false));
+  MPM.addPass(buildModuleSimplificationPipeline(Level, ThinLTOPhase::None,
+                                                DebugLogging));
 
   // Now add the optimization pipeline.
   MPM.addPass(buildModuleOptimizationPipeline(Level, DebugLogging));
@@ -807,8 +808,8 @@
   // If we are planning to perform ThinLTO later, we don't bloat the code with
   // unrolling/vectorization/... now. Just simplify the module as much as we
   // can.
-  MPM.addPass(buildModuleSimplificationPipeline(Level, DebugLogging,
-                                                /*PrepareForThinLTO=*/true));
+  MPM.addPass(buildModuleSimplificationPipeline(Level, ThinLTOPhase::PreLink,
+                                                DebugLogging));
 
   // Run partial inlining pass to partially inline functions that have
   // large bodies.
@@ -846,8 +847,8 @@
                             !PGOOpt->ProfileUseFile.empty()));
 
   // Add the core simplification pipeline.
-  MPM.addPass(buildModuleSimplificationPipeline(Level, DebugLogging,
-                                                /*PrepareForThinLTO=*/false));
+  MPM.addPass(buildModuleSimplificationPipeline(Level, ThinLTOPhase::PostLink,
+                                                DebugLogging));
 
   // Now add the optimization pipeline.
   MPM.addPass(buildModuleOptimizationPipeline(Level, DebugLogging));