[ctxprof] Use the flattened contextual profile pre-thinlink (#134723)

Flatten the profile pre-thinlink so that ThinLTO has something to work with for the parts of the binary that aren't covered by contextual profiles. Post-thinlink, the flattener is re-run and will actually change profile info, but just for the modules containing contextual trees ("specialized modules"). For the rest, the flattener just yanks out the instrumentation.

Author: mtrofin

llvm/include/llvm/Analysis/CtxProfAnalysis.h

@@ -61,7 +61,7 @@ class PGOContextualProfile {
 
   const PGOCtxProfile &profiles() const { return Profiles; }
 
-  bool isInSpecializedModule() const { return IsInSpecializedModule; }
+  bool isInSpecializedModule() const;
 
   bool isFunctionKnown(const Function &F) const {
     return getDefinedFunctionGUID(F) != 0;

llvm/include/llvm/Analysis/ProfileSummaryInfo.h

@@ -63,8 +63,9 @@ class ProfileSummaryInfo {
   ProfileSummaryInfo(const Module &M) : M(&M) { refresh(); }
   ProfileSummaryInfo(ProfileSummaryInfo &&Arg) = default;
 
-  /// If no summary is present, attempt to refresh.
-  void refresh();
+  /// If a summary is provided as argument, use that. Otherwise,
+  /// if the `Summary` member is null, attempt to refresh.
+  void refresh(std::unique_ptr<ProfileSummary> &&Other = nullptr);
 
   /// Returns true if profile summary is available.
   bool hasProfileSummary() const { return Summary != nullptr; }

llvm/include/llvm/Transforms/Instrumentation/PGOCtxProfFlattening.h

@@ -17,8 +17,11 @@ namespace llvm {
 
 class PGOCtxProfFlatteningPass
     : public PassInfoMixin<PGOCtxProfFlatteningPass> {
+  const bool IsPreThinlink;
+
 public:
-  explicit PGOCtxProfFlatteningPass() = default;
+  explicit PGOCtxProfFlatteningPass(bool IsPreThinlink)
+      : IsPreThinlink(IsPreThinlink) {}
   PreservedAnalyses run(Module &M, ModuleAnalysisManager &MAM);
 };
 } // namespace llvm

llvm/lib/Analysis/CtxProfAnalysis.cpp

@@ -39,6 +39,11 @@ static cl::opt<CtxProfAnalysisPrinterPass::PrintMode> PrintLevel(
                           "just the yaml representation of the profile")),
     cl::desc("Verbosity level of the contextual profile printer pass."));
 
+static cl::opt<bool> ForceIsInSpecializedModule(
+    "ctx-profile-force-is-specialized", cl::init(false),
+    cl::desc("Treat the given module as-if it were containing the "
+             "post-thinlink module containing the root"));
+
 const char *AssignGUIDPass::GUIDMetadataName = "guid";
 
 PreservedAnalyses AssignGUIDPass::run(Module &M, ModuleAnalysisManager &MAM) {
@@ -278,6 +283,12 @@ void PGOContextualProfile::initIndex() {
       });
 }
 
+bool PGOContextualProfile::isInSpecializedModule() const {
+  return ForceIsInSpecializedModule.getNumOccurrences() > 0
+             ? ForceIsInSpecializedModule
+             : IsInSpecializedModule;
+}
+
 void PGOContextualProfile::update(Visitor V, const Function &F) {
   assert(isFunctionKnown(F));
   GlobalValue::GUID G = getDefinedFunctionGUID(F);
@@ -299,20 +310,27 @@ void PGOContextualProfile::visit(ConstVisitor V, const Function *F) const {
 
 const CtxProfFlatProfile PGOContextualProfile::flatten() const {
   CtxProfFlatProfile Flat;
+  auto Accummulate = [](SmallVectorImpl<uint64_t> &Into,
+                        const SmallVectorImpl<uint64_t> &From) {
+    if (Into.empty())
+      Into.resize(From.size());
+    assert(Into.size() == From.size() &&
+           "All contexts corresponding to a function should have the exact "
+           "same number of counters.");
+    for (size_t I = 0, E = Into.size(); I < E; ++I)
+      Into[I] += From[I];
+  };
+
   preorderVisit<const PGOCtxProfContext::CallTargetMapTy,
                 const PGOCtxProfContext>(
       Profiles.Contexts, [&](const PGOCtxProfContext &Ctx) {
-        auto [It, Ins] = Flat.insert({Ctx.guid(), {}});
-        if (Ins) {
-          llvm::append_range(It->second, Ctx.counters());
-          return;
-        }
-        assert(It->second.size() == Ctx.counters().size() &&
-               "All contexts corresponding to a function should have the exact "
-               "same number of counters.");
-        for (size_t I = 0, E = It->second.size(); I < E; ++I)
-          It->second[I] += Ctx.counters()[I];
+        Accummulate(Flat[Ctx.guid()], Ctx.counters());
       });
+  for (const auto &[_, RC] : Profiles.Contexts)
+    for (const auto &[G, Unh] : RC.getUnhandled())
+      Accummulate(Flat[G], Unh);
+  for (const auto &[G, FC] : Profiles.FlatProfiles)
+    Accummulate(Flat[G], FC);
   return Flat;
 }
 

llvm/lib/Analysis/ProfileSummaryInfo.cpp

@@ -47,7 +47,11 @@ static cl::opt<double> PartialSampleProfileWorkingSetSizeScaleFactor(
 // any backend passes (IR level instrumentation, for example). This method
 // checks if the Summary is null and if so checks if the summary metadata is now
 // available in the module and parses it to get the Summary object.
-void ProfileSummaryInfo::refresh() {
+void ProfileSummaryInfo::refresh(std::unique_ptr<ProfileSummary> &&Other) {
+  if (Other) {
+    Summary.swap(Other);
+    return;
+  }
   if (hasProfileSummary())
     return;
   // First try to get context sensitive ProfileSummary.

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -1048,7 +1048,7 @@ PassBuilder::buildModuleInlinerPipeline(OptimizationLevel Level,
   if (!UseCtxProfile.empty() && Phase == ThinOrFullLTOPhase::ThinLTOPostLink) {
     MPM.addPass(GlobalOptPass());
     MPM.addPass(GlobalDCEPass());
-    MPM.addPass(PGOCtxProfFlatteningPass());
+    MPM.addPass(PGOCtxProfFlatteningPass(/*IsPreThinlink=*/false));
   }
 
   MPM.addPass(createModuleToFunctionPassAdaptor(
@@ -1242,8 +1242,10 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
     // FIXME(mtrofin): move AssignGUIDPass if there is agreement to use this
     // mechanism for GUIDs.
     MPM.addPass(AssignGUIDPass());
-    if (IsCtxProfUse)
+    if (IsCtxProfUse) {
+      MPM.addPass(PGOCtxProfFlatteningPass(/*IsPreThinlink=*/true));
       return MPM;
+    }
     // Block further inlining in the instrumented ctxprof case. This avoids
     // confusingly collecting profiles for the same GUID corresponding to
     // different variants of the function. We could do like PGO and identify

llvm/lib/Passes/PassRegistry.def

@@ -61,7 +61,9 @@ MODULE_PASS("coro-early", CoroEarlyPass())
 MODULE_PASS("cross-dso-cfi", CrossDSOCFIPass())
 MODULE_PASS("ctx-instr-gen",
             PGOInstrumentationGen(PGOInstrumentationType::CTXPROF))
-MODULE_PASS("ctx-prof-flatten", PGOCtxProfFlatteningPass())
+MODULE_PASS("ctx-prof-flatten", PGOCtxProfFlatteningPass(/*IsPreThinlink=*/false))
+MODULE_PASS("ctx-prof-flatten-prethinlink",
+            PGOCtxProfFlatteningPass(/*IsPreThinlink=*/true))
 MODULE_PASS("noinline-nonprevailing", NoinlineNonPrevailing())
 MODULE_PASS("deadargelim", DeadArgumentEliminationPass())
 MODULE_PASS("debugify", NewPMDebugifyPass())

llvm/lib/Transforms/Instrumentation/PGOCtxProfFlattening.cpp

@@ -185,7 +185,6 @@ class ProfileAnnotator final {
   // To be accessed through getBBInfo() after construction.
   std::map<const BasicBlock *, BBInfo> BBInfos;
   std::vector<EdgeInfo> EdgeInfos;
-  InstrProfSummaryBuilder &PB;
 
   // This is an adaptation of PGOUseFunc::populateCounters.
   // FIXME(mtrofin): look into factoring the code to share one implementation.
@@ -284,9 +283,8 @@ class ProfileAnnotator final {
   }
 
 public:
-  ProfileAnnotator(Function &F, const SmallVectorImpl<uint64_t> &Counters,
-                   InstrProfSummaryBuilder &PB)
-      : F(F), Counters(Counters), PB(PB) {
+  ProfileAnnotator(Function &F, const SmallVectorImpl<uint64_t> &Counters)
+      : F(F), Counters(Counters) {
     assert(!F.isDeclaration());
     assert(!Counters.empty());
     size_t NrEdges = 0;
@@ -351,8 +349,6 @@ class ProfileAnnotator final {
               (TotalCount > TrueCount ? TotalCount - TrueCount : 0U);
           setProfMetadata(F.getParent(), SI, {TrueCount, FalseCount},
                           std::max(TrueCount, FalseCount));
-          PB.addInternalCount(TrueCount);
-          PB.addInternalCount(FalseCount);
         }
       }
     }
@@ -364,7 +360,6 @@ class ProfileAnnotator final {
     assert(!Counters.empty());
     propagateCounterValues(Counters);
     F.setEntryCount(Counters[0]);
-    PB.addEntryCount(Counters[0]);
 
     for (auto &BB : F) {
       const auto &BBInfo = getBBInfo(BB);
@@ -381,7 +376,6 @@ class ProfileAnnotator final {
         if (EdgeCount > MaxCount)
           MaxCount = EdgeCount;
         EdgeCounts[SuccIdx] = EdgeCount;
-        PB.addInternalCount(EdgeCount);
       }
 
       if (MaxCount != 0)
@@ -431,16 +425,20 @@ PreservedAnalyses PGOCtxProfFlatteningPass::run(Module &M,
   // e.g. synthetic weights, etc) because it wouldn't interfere with the
   // contextual - based one (which would be in other modules)
   auto OnExit = llvm::make_scope_exit([&]() {
+    if (IsPreThinlink)
+      return;
     for (auto &F : M)
       removeInstrumentation(F);
   });
   auto &CtxProf = MAM.getResult<CtxProfAnalysis>(M);
-  if (CtxProf.contexts().empty())
+  // post-thinlink, we only reprocess for the module(s) containing the
+  // contextual tree. For everything else, OnExit will just clean the
+  // instrumentation.
+  if (!IsPreThinlink && !CtxProf.isInSpecializedModule())
     return PreservedAnalyses::none();
 
   const auto FlattenedProfile = CtxProf.flatten();
 
-  InstrProfSummaryBuilder PB(ProfileSummaryBuilder::DefaultCutoffs);
   for (auto &F : M) {
     if (F.isDeclaration())
       continue;
@@ -456,15 +454,26 @@ PreservedAnalyses PGOCtxProfFlatteningPass::run(Module &M,
     if (It == FlattenedProfile.end())
       clearColdFunctionProfile(F);
     else {
-      ProfileAnnotator S(F, It->second, PB);
+      ProfileAnnotator S(F, It->second);
       S.assignProfileData();
     }
   }
-
-  auto &PSI = MAM.getResult<ProfileSummaryAnalysis>(M);
+  InstrProfSummaryBuilder PB(ProfileSummaryBuilder::DefaultCutoffs);
+  // use here the flat profiles just so the importer doesn't complain about
+  // how different the PSIs are between the module with the roots and the
+  // various modules it imports.
+  for (auto &C : FlattenedProfile) {
+    PB.addEntryCount(C.second[0]);
+    for (auto V : llvm::drop_begin(C.second))
+      PB.addInternalCount(V);
+  }
 
   M.setProfileSummary(PB.getSummary()->getMD(M.getContext()),
                       ProfileSummary::Kind::PSK_Instr);
-  PSI.refresh();
+  PreservedAnalyses PA;
+  PA.abandon<ProfileSummaryAnalysis>();
+  MAM.invalidate(M, PA);
+  auto &PSI = MAM.getResult<ProfileSummaryAnalysis>(M);
+  PSI.refresh(PB.getSummary());
   return PreservedAnalyses::none();
 }

llvm/test/Analysis/CtxProfAnalysis/flatten-and-annotate.ll

@@ -4,9 +4,10 @@
 ; RUN: split-file %s %t
 ; RUN: llvm-ctxprof-util fromYAML --input=%t/profile.yaml --output=%t/profile.ctxprofdata
 ; RUN: opt -module-summary -passes='thinlto-pre-link<O2>' -use-ctx-profile=%t/profile.ctxprofdata \
-; RUN:   %t/example.ll -S -o %t/prelink.ll
-; RUN: FileCheck --input-file %t/prelink.ll %s --check-prefix=PRELINK
-; RUN: opt -passes='ctx-prof-flatten' -use-ctx-profile=%t/profile.ctxprofdata %t/prelink.ll -S  | FileCheck %s
+; RUN:   %t/example.ll -S -o %t/4909520559318251808.ll
+; RUN: FileCheck --input-file %t/4909520559318251808.ll %s --check-prefix=PRELINK
+
+; RUN: opt -passes='ctx-prof-flatten' -use-ctx-profile=%t/profile.ctxprofdata %t/4909520559318251808.ll -S  | FileCheck %s --check-prefix=POSTLINK
 ;
 ;
 ; Check that instrumentation occurs where expected: the "no" block for both foo and
@@ -18,57 +19,73 @@
 ; PRELINK-NEXT:     call void @llvm.instrprof.increment(ptr @foo, i64 [[#]], i32 2, i32 1)
 
 ; PRELINK-LABEL: @an_entrypoint
+; PRELINK:       br i1 %t, label %yes, label %common.ret, !prof ![[PREPROF:[0-9]+]]
 ; PRELINK-LABEL: yes:
 ; PRELINK-NEXT:    call void @llvm.instrprof.increment(ptr @an_entrypoint, i64 [[#]], i32 2, i32 1)
-; PRELINK-NOT: "ProfileSummary"
+; PRELINK:      ![[#]] = !{i32 1, !"ProfileSummary", !1}
+; PRELINK:      ![[#]] = !{!"TotalCount", i64 3595}
+; PRELINK:      ![[#]] = !{!"MaxCount", i64 3000}
+; PRELINK:      ![[#]] = !{!"MaxInternalCount", i64 3000}
+; PRELINK:      ![[#]] = !{!"MaxFunctionCount", i64 300}
+; PRELINK:      ![[#]] = !{!"NumCounts", i64 6}
+; PRELINK:      ![[#]] = !{!"NumFunctions", i64 3}
+; PRELINK:       ![[PREPROF]] = !{!"branch_weights", i32 40, i32 60}
 
 ; Check that the output has:
 ;  - no instrumentation
 ;  - the 2 functions have an entry count
 ;  - each conditional branch has profile annotation
 ;
-; CHECK-NOT:   call void @llvm.instrprof
+; POSTLINK-NOT:   call void @llvm.instrprof
 ;
 ; make sure we have function entry counts, branch weights, and a profile summary.
-; CHECK-LABEL: @foo
-; CHECK-SAME:    !prof ![[FOO_EP:[0-9]+]]
-; CHECK:          br i1 %t, label %yes, label %no, !prof ![[FOO_BW:[0-9]+]]
-; CHECK-LABEL: @an_entrypoint
-; CHECK-SAME:    !prof ![[AN_ENTRYPOINT_EP:[0-9]+]]
-; CHECK:          br i1 %t, label %yes, label %common.ret, !prof ![[AN_ENTRYPOINT_BW:[0-9]+]]
+; POSTLINK-LABEL: @foo
+; POSTLINK-SAME:    !prof ![[FOO_EP:[0-9]+]]
+; POSTLINK:          br i1 %t, label %yes, label %no, !prof ![[FOO_BW:[0-9]+]]
+; POSTLINK-LABEL: @an_entrypoint
+; POSTLINK-SAME:    !prof ![[AN_ENTRYPOINT_EP:[0-9]+]]
+; POSTLINK:          br i1 %t, label %yes, label %common.ret, !prof ![[AN_ENTRYPOINT_BW:[0-9]+]]
 
+; The postlink summary is restricted to the stuff under the root - including the
+; "unhandled" data.
+; POSTLINK:      ![[#]] = !{i32 1, !"ProfileSummary", !1}
+; POSTLINK:      ![[#]] = !{!"TotalCount", i64 1495}
+; POSTLINK:      ![[#]] = !{!"MaxCount", i64 1000}
+; POSTLINK:      ![[#]] = !{!"MaxInternalCount", i64 1000}
+; POSTLINK:      ![[#]] = !{!"MaxFunctionCount", i64 200}
+; POSTLINK:      ![[#]] = !{!"NumCounts", i64 6}
+; POSTLINK:      ![[#]] = !{!"NumFunctions", i64 3}
 
-; CHECK:      ![[#]] = !{i32 1, !"ProfileSummary", !1}
-; CHECK:      ![[#]] = !{!"TotalCount", i64 480}
-; CHECK:      ![[#]] = !{!"MaxCount", i64 140}
-; CHECK:      ![[#]] = !{!"MaxInternalCount", i64 125}
-; CHECK:      ![[#]] = !{!"MaxFunctionCount", i64 140}
-; CHECK:      ![[#]] = !{!"NumCounts", i64 6}
-; CHECK:      ![[#]] = !{!"NumFunctions", i64 2}
 ;
 ; @foo will be called both unconditionally and conditionally, on the "yes" branch
 ; which has a count of 40. So 140 times.
 
-; CHECK:       ![[FOO_EP]] = !{!"function_entry_count", i64 140} 
+; POSTLINK:       ![[FOO_EP]] = !{!"function_entry_count", i64 140} 
 
 ; foo's "no" branch is taken 10+5 times (from the 2 contexts belonging to foo).
 ; Which means its "yes" branch is taken 140 - 15 times.
 
-; CHECK:       ![[FOO_BW]] = !{!"branch_weights", i32 125, i32 15} 
-; CHECK:       ![[AN_ENTRYPOINT_EP]] = !{!"function_entry_count", i64 100}
-; CHECK:       ![[AN_ENTRYPOINT_BW]] = !{!"branch_weights", i32 40, i32 60} 
+; POSTLINK:       ![[FOO_BW]] = !{!"branch_weights", i32 125, i32 15} 
+; POSTLINK:       ![[AN_ENTRYPOINT_EP]] = !{!"function_entry_count", i64 100}
+; POSTLINK:       ![[AN_ENTRYPOINT_BW]] = !{!"branch_weights", i32 40, i32 60} 
 
 ;--- profile.yaml
 Contexts:
   - Guid: 4909520559318251808
     TotalRootEntryCount: 100
+    Unhandled:
+      - Guid: 1234
+        Counters: [200, 1000]
     Counters: [100, 40]
     Callsites: -
                 - Guid: 11872291593386833696
                   Counters: [ 100, 5 ]
                -
                 - Guid: 11872291593386833696
                   Counters: [ 40, 10 ]
+FlatProfiles:
+  - Guid: 1234
+    Counters: [ 100, 2000 ]
 ;--- example.ll
 declare void @bar()
 

llvm/test/Analysis/CtxProfAnalysis/flatten-check-path.ll

@@ -7,9 +7,9 @@
 ; RUN: llvm-ctxprof-util fromYAML --input=%t/profile_pump.yaml --output=%t/profile_pump.ctxprofdata
 ; RUN: llvm-ctxprof-util fromYAML --input=%t/profile_unreachable.yaml --output=%t/profile_unreachable.ctxprofdata
 ;
-; RUN: opt -passes=ctx-prof-flatten %t/example_ok.ll -use-ctx-profile=%t/profile_ok.ctxprofdata -S -o - | FileCheck %s
-; RUN: not --crash opt -passes=ctx-prof-flatten %t/message_pump.ll -use-ctx-profile=%t/profile_pump.ctxprofdata -S 2>&1 | FileCheck %s --check-prefix=ASSERTION
-; RUN: not --crash opt -passes=ctx-prof-flatten %t/unreachable.ll -use-ctx-profile=%t/profile_unreachable.ctxprofdata -S 2>&1 | FileCheck %s --check-prefix=ASSERTION
+; RUN: opt -passes=ctx-prof-flatten %t/example_ok.ll -ctx-profile-force-is-specialized -use-ctx-profile=%t/profile_ok.ctxprofdata -S -o - | FileCheck %s
+; RUN: not --crash opt -passes=ctx-prof-flatten %t/message_pump.ll -ctx-profile-force-is-specialized -use-ctx-profile=%t/profile_pump.ctxprofdata -S 2>&1 | FileCheck %s --check-prefix=ASSERTION
+; RUN: not --crash opt -passes=ctx-prof-flatten %t/unreachable.ll -ctx-profile-force-is-specialized -use-ctx-profile=%t/profile_unreachable.ctxprofdata -S 2>&1 | FileCheck %s --check-prefix=ASSERTION
 
 ; CHECK: br i1 %x, label %b1, label %exit, !prof ![[PROF1:[0-9]+]]
 ; CHECK: br i1 %y, label %blk, label %exit, !prof ![[PROF2:[0-9]+]]