[ctx_prof] Add support for ICP (#105469)

An overload of `llvm::promoteCallWithIfThenElse` that updates the contextual profile.

High-level, this is very simple: after creating the `if... then (direct call) else (indirect call)` structure, we instrument the new callsites and BBs (the instrumentation will help with tracking for other IPO transformations, and, ultimately, to match counter values before flattening to `MD_prof`).

In more detail:

- move the callsite instrumentation of the indirect call to the `else` BB, before the indirect call
- create a new callsite instrumentation for the direct call
- create instrumentation for both the `then` and `else` BBs - we could instrument just one (MST-style) but we're not running the binary with this instrumentation, and at most this would save some space (less counters tracked). For simplicity instrumenting both at this point
- update each context belonging to the caller by updating the counters, and moving the indirect callee to the new, direct callsite ID

Issue #89287

Author: mtrofin

llvm/include/llvm/Analysis/CtxProfAnalysis.h

@@ -73,6 +73,12 @@ class PGOContextualProfile {
     return FuncInfo.find(getDefinedFunctionGUID(F))->second.NextCallsiteIndex++;
   }
 
+  using ConstVisitor = function_ref<void(const PGOCtxProfContext &)>;
+  using Visitor = function_ref<void(PGOCtxProfContext &)>;
+
+  void update(Visitor, const Function *F = nullptr);
+  void visit(ConstVisitor, const Function *F = nullptr) const;
+
   const CtxProfFlatProfile flatten() const;
 
   bool invalidate(Module &, const PreservedAnalyses &PA,
@@ -105,13 +111,18 @@ class CtxProfAnalysis : public AnalysisInfoMixin<CtxProfAnalysis> {
 
 class CtxProfAnalysisPrinterPass
     : public PassInfoMixin<CtxProfAnalysisPrinterPass> {
-  raw_ostream &OS;
-
 public:
-  explicit CtxProfAnalysisPrinterPass(raw_ostream &OS) : OS(OS) {}
+  enum class PrintMode { Everything, JSON };
+  explicit CtxProfAnalysisPrinterPass(raw_ostream &OS,
+                                      PrintMode Mode = PrintMode::Everything)
+      : OS(OS), Mode(Mode) {}
 
   PreservedAnalyses run(Module &M, ModuleAnalysisManager &MAM);
   static bool isRequired() { return true; }
+
+private:
+  raw_ostream &OS;
+  const PrintMode Mode;
 };
 
 /// Assign a GUID to functions as metadata. GUID calculation takes linkage into

llvm/include/llvm/IR/IntrinsicInst.h

@@ -1535,6 +1535,7 @@ class InstrProfCntrInstBase : public InstrProfInstBase {
   ConstantInt *getNumCounters() const;
   // The index of the counter that this instruction acts on.
   ConstantInt *getIndex() const;
+  void setIndex(uint32_t Idx);
 };
 
 /// This represents the llvm.instrprof.cover intrinsic.
@@ -1585,6 +1586,7 @@ class InstrProfCallsite : public InstrProfCntrInstBase {
     return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
   }
   Value *getCallee() const;
+  void setCallee(Value *Callee);
 };
 
 /// This represents the llvm.instrprof.timestamp intrinsic.

llvm/include/llvm/ProfileData/PGOCtxProfReader.h

@@ -57,9 +57,25 @@ class PGOCtxProfContext final {
 
   GlobalValue::GUID guid() const { return GUID; }
   const SmallVectorImpl<uint64_t> &counters() const { return Counters; }
+  SmallVectorImpl<uint64_t> &counters() { return Counters; }
+
+  uint64_t getEntrycount() const {
+    assert(!Counters.empty() &&
+           "Functions are expected to have at their entry BB instrumented, so "
+           "there should always be at least 1 counter.");
+    return Counters[0];
+  }
+
   const CallsiteMapTy &callsites() const { return Callsites; }
   CallsiteMapTy &callsites() { return Callsites; }
 
+  void ingestContext(uint32_t CSId, PGOCtxProfContext &&Other) {
+    auto [Iter, _] = callsites().try_emplace(CSId, CallTargetMapTy());
+    Iter->second.emplace(Other.guid(), std::move(Other));
+  }
+
+  void resizeCounters(uint32_t Size) { Counters.resize(Size); }
+
   bool hasCallsite(uint32_t I) const {
     return Callsites.find(I) != Callsites.end();
   }
@@ -68,6 +84,12 @@ class PGOCtxProfContext final {
     assert(hasCallsite(I) && "Callsite not found");
     return Callsites.find(I)->second;
   }
+
+  CallTargetMapTy &callsite(uint32_t I) {
+    assert(hasCallsite(I) && "Callsite not found");
+    return Callsites.find(I)->second;
+  }
+
   void getContainedGuids(DenseSet<GlobalValue::GUID> &Guids) const;
 };
 

llvm/include/llvm/Transforms/Utils/CallPromotionUtils.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_TRANSFORMS_UTILS_CALLPROMOTIONUTILS_H
 #define LLVM_TRANSFORMS_UTILS_CALLPROMOTIONUTILS_H
 
+#include "llvm/Analysis/CtxProfAnalysis.h"
 namespace llvm {
 template <typename T> class ArrayRef;
 class Constant;
@@ -56,6 +57,9 @@ CallBase &promoteCall(CallBase &CB, Function *Callee,
 CallBase &promoteCallWithIfThenElse(CallBase &CB, Function *Callee,
                                     MDNode *BranchWeights = nullptr);
 
+CallBase *promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
+                                    PGOContextualProfile &CtxProf);
+
 /// This is similar to `promoteCallWithIfThenElse` except that the condition to
 /// promote a virtual call is that \p VPtr is the same as any of \p
 /// AddressPoints.

llvm/lib/Analysis/CtxProfAnalysis.cpp

@@ -173,16 +173,22 @@ PreservedAnalyses CtxProfAnalysisPrinterPass::run(Module &M,
     return PreservedAnalyses::all();
   }
 
-  OS << "Function Info:\n";
-  for (const auto &[Guid, FuncInfo] : C.FuncInfo)
-    OS << Guid << " : " << FuncInfo.Name
-       << ". MaxCounterID: " << FuncInfo.NextCounterIndex
-       << ". MaxCallsiteID: " << FuncInfo.NextCallsiteIndex << "\n";
+  if (Mode == PrintMode::Everything) {
+    OS << "Function Info:\n";
+    for (const auto &[Guid, FuncInfo] : C.FuncInfo)
+      OS << Guid << " : " << FuncInfo.Name
+         << ". MaxCounterID: " << FuncInfo.NextCounterIndex
+         << ". MaxCallsiteID: " << FuncInfo.NextCallsiteIndex << "\n";
+  }
 
   const auto JSONed = ::llvm::json::toJSON(C.profiles());
 
-  OS << "\nCurrent Profile:\n";
+  if (Mode == PrintMode::Everything)
+    OS << "\nCurrent Profile:\n";
   OS << formatv("{0:2}", JSONed);
+  if (Mode == PrintMode::JSON)
+    return PreservedAnalyses::all();
+
   OS << "\n";
   OS << "\nFlat Profile:\n";
   auto Flat = C.flatten();
@@ -209,34 +215,49 @@ InstrProfIncrementInst *CtxProfAnalysis::getBBInstrumentation(BasicBlock &BB) {
   return nullptr;
 }
 
-static void
-preorderVisit(const PGOCtxProfContext::CallTargetMapTy &Profiles,
-              function_ref<void(const PGOCtxProfContext &)> Visitor) {
-  std::function<void(const PGOCtxProfContext &)> Traverser =
-      [&](const auto &Ctx) {
-        Visitor(Ctx);
-        for (const auto &[_, SubCtxSet] : Ctx.callsites())
-          for (const auto &[__, Subctx] : SubCtxSet)
-            Traverser(Subctx);
-      };
-  for (const auto &[_, P] : Profiles)
+template <class ProfilesTy, class ProfTy>
+static void preorderVisit(ProfilesTy &Profiles,
+                          function_ref<void(ProfTy &)> Visitor,
+                          GlobalValue::GUID Match = 0) {
+  std::function<void(ProfTy &)> Traverser = [&](auto &Ctx) {
+    if (!Match || Ctx.guid() == Match)
+      Visitor(Ctx);
+    for (auto &[_, SubCtxSet] : Ctx.callsites())
+      for (auto &[__, Subctx] : SubCtxSet)
+        Traverser(Subctx);
+  };
+  for (auto &[_, P] : Profiles)
     Traverser(P);
 }
 
+void PGOContextualProfile::update(Visitor V, const Function *F) {
+  GlobalValue::GUID G = F ? getDefinedFunctionGUID(*F) : 0U;
+  preorderVisit<PGOCtxProfContext::CallTargetMapTy, PGOCtxProfContext>(
+      *Profiles, V, G);
+}
+
+void PGOContextualProfile::visit(ConstVisitor V, const Function *F) const {
+  GlobalValue::GUID G = F ? getDefinedFunctionGUID(*F) : 0U;
+  preorderVisit<const PGOCtxProfContext::CallTargetMapTy,
+                const PGOCtxProfContext>(*Profiles, V, G);
+}
+
 const CtxProfFlatProfile PGOContextualProfile::flatten() const {
   assert(Profiles.has_value());
   CtxProfFlatProfile Flat;
-  preorderVisit(*Profiles, [&](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];
-  });
+  preorderVisit<const PGOCtxProfContext::CallTargetMapTy,
+                const PGOCtxProfContext>(
+      *Profiles, [&](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];
+      });
   return Flat;
 }

llvm/lib/IR/IntrinsicInst.cpp

@@ -285,6 +285,11 @@ ConstantInt *InstrProfCntrInstBase::getIndex() const {
   return cast<ConstantInt>(const_cast<Value *>(getArgOperand(3)));
 }
 
+void InstrProfCntrInstBase::setIndex(uint32_t Idx) {
+  assert(isa<InstrProfCntrInstBase>(this));
+  setArgOperand(3, ConstantInt::get(Type::getInt32Ty(getContext()), Idx));
+}
+
 Value *InstrProfIncrementInst::getStep() const {
   if (InstrProfIncrementInstStep::classof(this)) {
     return const_cast<Value *>(getArgOperand(4));
@@ -300,6 +305,11 @@ Value *InstrProfCallsite::getCallee() const {
   return nullptr;
 }
 
+void InstrProfCallsite::setCallee(Value *Callee) {
+  assert(isa<InstrProfCallsite>(this));
+  setArgOperand(4, Callee);
+}
+
 std::optional<RoundingMode> ConstrainedFPIntrinsic::getRoundingMode() const {
   unsigned NumOperands = arg_size();
   Metadata *MD = nullptr;

llvm/lib/Transforms/Utils/CallPromotionUtils.cpp

@@ -12,14 +12,16 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Utils/CallPromotionUtils.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/CtxProfAnalysis.h"
 #include "llvm/Analysis/Loads.h"
 #include "llvm/Analysis/TypeMetadataUtils.h"
 #include "llvm/IR/AttributeMask.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
+#include "llvm/ProfileData/PGOCtxProfReader.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 
 using namespace llvm;
@@ -572,6 +574,88 @@ CallBase &llvm::promoteCallWithIfThenElse(CallBase &CB, Function *Callee,
   return promoteCall(NewInst, Callee);
 }
 
+CallBase *llvm::promoteCallWithIfThenElse(CallBase &CB, Function &Callee,
+                                          PGOContextualProfile &CtxProf) {
+  assert(CB.isIndirectCall());
+  if (!CtxProf.isFunctionKnown(Callee))
+    return nullptr;
+  auto &Caller = *CB.getFunction();
+  auto *CSInstr = CtxProfAnalysis::getCallsiteInstrumentation(CB);
+  if (!CSInstr)
+    return nullptr;
+  const uint64_t CSIndex = CSInstr->getIndex()->getZExtValue();
+
+  CallBase &DirectCall = promoteCall(
+      versionCallSite(CB, &Callee, /*BranchWeights=*/nullptr), &Callee);
+  CSInstr->moveBefore(&CB);
+  const auto NewCSID = CtxProf.allocateNextCallsiteIndex(Caller);
+  auto *NewCSInstr = cast<InstrProfCallsite>(CSInstr->clone());
+  NewCSInstr->setIndex(NewCSID);
+  NewCSInstr->setCallee(&Callee);
+  NewCSInstr->insertBefore(&DirectCall);
+  auto &DirectBB = *DirectCall.getParent();
+  auto &IndirectBB = *CB.getParent();
+
+  assert((CtxProfAnalysis::getBBInstrumentation(IndirectBB) == nullptr) &&
+         "The ICP direct BB is new, it shouldn't have instrumentation");
+  assert((CtxProfAnalysis::getBBInstrumentation(DirectBB) == nullptr) &&
+         "The ICP indirect BB is new, it shouldn't have instrumentation");
+
+  // Allocate counters for the new basic blocks.
+  const uint32_t DirectID = CtxProf.allocateNextCounterIndex(Caller);
+  const uint32_t IndirectID = CtxProf.allocateNextCounterIndex(Caller);
+  auto *EntryBBIns =
+      CtxProfAnalysis::getBBInstrumentation(Caller.getEntryBlock());
+  auto *DirectBBIns = cast<InstrProfCntrInstBase>(EntryBBIns->clone());
+  DirectBBIns->setIndex(DirectID);
+  DirectBBIns->insertInto(&DirectBB, DirectBB.getFirstInsertionPt());
+
+  auto *IndirectBBIns = cast<InstrProfCntrInstBase>(EntryBBIns->clone());
+  IndirectBBIns->setIndex(IndirectID);
+  IndirectBBIns->insertInto(&IndirectBB, IndirectBB.getFirstInsertionPt());
+
+  const GlobalValue::GUID CalleeGUID = AssignGUIDPass::getGUID(Callee);
+  const uint32_t NewCountersSize = IndirectID + 1;
+
+  auto ProfileUpdater = [&](PGOCtxProfContext &Ctx) {
+    assert(Ctx.guid() == AssignGUIDPass::getGUID(Caller));
+    assert(NewCountersSize - 2 == Ctx.counters().size());
+    // All the ctx-es belonging to a function must have the same size counters.
+    Ctx.resizeCounters(NewCountersSize);
+
+    // Maybe in this context, the indirect callsite wasn't observed at all
+    if (!Ctx.hasCallsite(CSIndex))
+      return;
+    auto &CSData = Ctx.callsite(CSIndex);
+    auto It = CSData.find(CalleeGUID);
+
+    // Maybe we did notice the indirect callsite, but to other targets.
+    if (It == CSData.end())
+      return;
+
+    assert(CalleeGUID == It->second.guid());
+
+    uint32_t DirectCount = It->second.getEntrycount();
+    uint32_t TotalCount = 0;
+    for (const auto &[_, V] : CSData)
+      TotalCount += V.getEntrycount();
+    assert(TotalCount >= DirectCount);
+    uint32_t IndirectCount = TotalCount - DirectCount;
+    // The ICP's effect is as-if the direct BB would have been taken DirectCount
+    // times, and the indirect BB, IndirectCount times
+    Ctx.counters()[DirectID] = DirectCount;
+    Ctx.counters()[IndirectID] = IndirectCount;
+
+    // This particular indirect target needs to be moved to this caller under
+    // the newly-allocated callsite index.
+    assert(Ctx.callsites().count(NewCSID) == 0);
+    Ctx.ingestContext(NewCSID, std::move(It->second));
+    CSData.erase(CalleeGUID);
+  };
+  CtxProf.update(ProfileUpdater, &Caller);
+  return &DirectCall;
+}
+
 CallBase &llvm::promoteCallWithVTableCmp(CallBase &CB, Instruction *VPtr,
                                          Function *Callee,
                                          ArrayRef<Constant *> AddressPoints,