Index: include/llvm/IR/ModuleSummaryIndex.h =================================================================== --- include/llvm/IR/ModuleSummaryIndex.h +++ include/llvm/IR/ModuleSummaryIndex.h @@ -501,8 +501,9 @@ FunctionSummary::GVFlags( GlobalValue::LinkageTypes::AvailableExternallyLinkage, /*NotEligibleToImport=*/true, /*Live=*/true, /*IsLocal=*/false), - 0, FunctionSummary::FFlags{}, std::vector(), - std::move(Edges), std::vector(), + /*InsCount=*/0, FunctionSummary::FFlags{}, /*EntryCount=*/0, + std::vector(), std::move(Edges), + std::vector(), std::vector(), std::vector(), std::vector(), @@ -520,6 +521,11 @@ /// Function summary specific flags. FFlags FunFlags; + /// The synthesized entry count of the function. + /// This is only populated during ThinLink phase and remains unused while + /// generating per-module summaries. + uint64_t EntryCount = 0; + /// List of call edge pairs from this function. std::vector CallGraphEdgeList; @@ -527,14 +533,15 @@ public: FunctionSummary(GVFlags Flags, unsigned NumInsts, FFlags FunFlags, - std::vector Refs, std::vector CGEdges, + uint64_t EntryCount, std::vector Refs, + std::vector CGEdges, std::vector TypeTests, std::vector TypeTestAssumeVCalls, std::vector TypeCheckedLoadVCalls, std::vector TypeTestAssumeConstVCalls, std::vector TypeCheckedLoadConstVCalls) : GlobalValueSummary(FunctionKind, Flags, std::move(Refs)), - InstCount(NumInsts), FunFlags(FunFlags), + InstCount(NumInsts), FunFlags(FunFlags), EntryCount(EntryCount), CallGraphEdgeList(std::move(CGEdges)) { if (!TypeTests.empty() || !TypeTestAssumeVCalls.empty() || !TypeCheckedLoadVCalls.empty() || !TypeTestAssumeConstVCalls.empty() || @@ -559,6 +566,12 @@ /// Get the instruction count recorded for this function. unsigned instCount() const { return InstCount; } + /// Get the synthetic entry count for this function. + uint64_t entryCount() const { return EntryCount; } + + /// Set the synthetic entry count for this function. + void setEntryCount(uint64_t EC) { EntryCount = EC; } + /// Return the list of pairs. ArrayRef calls() const { return CallGraphEdgeList; } @@ -1158,6 +1171,7 @@ /// GraphTraits definition to build SCC for the index template <> struct GraphTraits { typedef ValueInfo NodeRef; + using EdgeRef = FunctionSummary::EdgeTy &; static NodeRef valueInfoFromEdge(FunctionSummary::EdgeTy &P) { return P.first; @@ -1166,6 +1180,8 @@ mapped_iterator::iterator, decltype(&valueInfoFromEdge)>; + using ChildEdgeIteratorType = std::vector::iterator; + static NodeRef getEntryNode(ValueInfo V) { return V; } static ChildIteratorType child_begin(NodeRef N) { @@ -1187,6 +1203,26 @@ cast(N.getSummaryList().front()->getBaseObject()); return ChildIteratorType(F->CallGraphEdgeList.end(), &valueInfoFromEdge); } + + static ChildEdgeIteratorType child_edge_begin(NodeRef N) { + if (!N.getSummaryList().size()) // handle external function + return FunctionSummary::ExternalNode.CallGraphEdgeList.begin(); + + FunctionSummary *F = + cast(N.getSummaryList().front()->getBaseObject()); + return F->CallGraphEdgeList.begin(); + } + + static ChildEdgeIteratorType child_edge_end(NodeRef N) { + if (!N.getSummaryList().size()) // handle external function + return FunctionSummary::ExternalNode.CallGraphEdgeList.end(); + + FunctionSummary *F = + cast(N.getSummaryList().front()->getBaseObject()); + return F->CallGraphEdgeList.end(); + } + + static NodeRef edge_dest(EdgeRef E) { return E.first; } }; template <> Index: include/llvm/IR/ModuleSummaryIndexYAML.h =================================================================== --- include/llvm/IR/ModuleSummaryIndexYAML.h +++ include/llvm/IR/ModuleSummaryIndexYAML.h @@ -224,7 +224,7 @@ GlobalValueSummary::GVFlags( static_cast(FSum.Linkage), FSum.NotEligibleToImport, FSum.Live, FSum.IsLocal), - 0, FunctionSummary::FFlags{}, Refs, + /*NumInsts=*/0, FunctionSummary::FFlags{}, /*EntryCount=*/0, Refs, ArrayRef{}, std::move(FSum.TypeTests), std::move(FSum.TypeTestAssumeVCalls), std::move(FSum.TypeCheckedLoadVCalls), Index: include/llvm/Transforms/Utils/FunctionImportUtils.h =================================================================== --- include/llvm/Transforms/Utils/FunctionImportUtils.h +++ include/llvm/Transforms/Utils/FunctionImportUtils.h @@ -113,6 +113,10 @@ bool renameModuleForThinLTO( Module &M, const ModuleSummaryIndex &Index, SetVector *GlobalsToImport = nullptr); + +/// Compute synthetic function entry counts. +void computeSyntheticCounts(ModuleSummaryIndex &Index); + } // End llvm namespace #endif Index: lib/Analysis/ModuleSummaryAnalysis.cpp =================================================================== --- lib/Analysis/ModuleSummaryAnalysis.cpp +++ lib/Analysis/ModuleSummaryAnalysis.cpp @@ -396,9 +396,9 @@ // Don't try to import functions with noinline attribute. F.getAttributes().hasFnAttribute(Attribute::NoInline)}; auto FuncSummary = llvm::make_unique( - Flags, NumInsts, FunFlags, std::move(Refs), CallGraphEdges.takeVector(), - TypeTests.takeVector(), TypeTestAssumeVCalls.takeVector(), - TypeCheckedLoadVCalls.takeVector(), + Flags, NumInsts, FunFlags, /*EntryCount=*/0, std::move(Refs), + CallGraphEdges.takeVector(), TypeTests.takeVector(), + TypeTestAssumeVCalls.takeVector(), TypeCheckedLoadVCalls.takeVector(), TypeTestAssumeConstVCalls.takeVector(), TypeCheckedLoadConstVCalls.takeVector()); if (NonRenamableLocal) @@ -509,14 +509,15 @@ if (Function *F = dyn_cast(GV)) { std::unique_ptr Summary = llvm::make_unique( - GVFlags, 0, + GVFlags, /*InstCount=*/0, FunctionSummary::FFlags{ F->hasFnAttribute(Attribute::ReadNone), F->hasFnAttribute(Attribute::ReadOnly), F->hasFnAttribute(Attribute::NoRecurse), F->returnDoesNotAlias(), /* NoInline = */ false}, - ArrayRef{}, ArrayRef{}, + /*EntryCount=*/0, ArrayRef{}, + ArrayRef{}, ArrayRef{}, ArrayRef{}, ArrayRef{}, Index: lib/Analysis/SyntheticCountsUtils.cpp =================================================================== --- lib/Analysis/SyntheticCountsUtils.cpp +++ lib/Analysis/SyntheticCountsUtils.cpp @@ -14,12 +14,12 @@ #include "llvm/Analysis/SyntheticCountsUtils.h" #include "llvm/ADT/DenseSet.h" #include "llvm/ADT/SCCIterator.h" -#include "llvm/ADT/SmallPtrSet.h" #include "llvm/Analysis/CallGraph.h" #include "llvm/IR/CallSite.h" #include "llvm/IR/Function.h" #include "llvm/IR/InstIterator.h" #include "llvm/IR/Instructions.h" +#include "llvm/IR/ModuleSummaryIndex.h" using namespace llvm; @@ -29,7 +29,7 @@ const SccTy &SCC, GetRelBBFreqTy GetRelBBFreq, GetCountTy GetCount, AddCountTy AddCount) { - SmallPtrSet SCCNodes; + DenseSet SCCNodes; SmallVector, 8> SCCEdges, NonSCCEdges; for (auto &Node : SCC) @@ -111,3 +111,4 @@ } template class llvm::SyntheticCountsUtils; +template class llvm::SyntheticCountsUtils; Index: lib/AsmParser/LLParser.cpp =================================================================== --- lib/AsmParser/LLParser.cpp +++ lib/AsmParser/LLParser.cpp @@ -7727,8 +7727,8 @@ return true; auto FS = llvm::make_unique( - GVFlags, InstCount, FFlags, std::move(Refs), std::move(Calls), - std::move(TypeIdInfo.TypeTests), + GVFlags, InstCount, FFlags, /*EntryCount=*/0, std::move(Refs), + std::move(Calls), std::move(TypeIdInfo.TypeTests), std::move(TypeIdInfo.TypeTestAssumeVCalls), std::move(TypeIdInfo.TypeCheckedLoadVCalls), std::move(TypeIdInfo.TypeTestAssumeConstVCalls), Index: lib/Bitcode/Reader/BitcodeReader.cpp =================================================================== --- lib/Bitcode/Reader/BitcodeReader.cpp +++ lib/Bitcode/Reader/BitcodeReader.cpp @@ -5247,9 +5247,9 @@ } const uint64_t Version = Record[0]; const bool IsOldProfileFormat = Version == 1; - if (Version < 1 || Version > 5) + if (Version < 1 || Version > 6) return error("Invalid summary version " + Twine(Version) + - ", 1, 2, 3, 4 or 5 expected"); + ". Version should be in the range [1-6]."); Record.clear(); // Keep around the last seen summary to be used when we see an optional @@ -5358,8 +5358,8 @@ IsOldProfileFormat, HasProfile, HasRelBF); setImmutableRefs(Refs, NumImmutableRefs); auto FS = llvm::make_unique( - Flags, InstCount, getDecodedFFlags(RawFunFlags), std::move(Refs), - std::move(Calls), std::move(PendingTypeTests), + Flags, InstCount, getDecodedFFlags(RawFunFlags), /*EntryCount=*/0, + std::move(Refs), std::move(Calls), std::move(PendingTypeTests), std::move(PendingTypeTestAssumeVCalls), std::move(PendingTypeCheckedLoadVCalls), std::move(PendingTypeTestAssumeConstVCalls), @@ -5437,18 +5437,25 @@ uint64_t RawFlags = Record[2]; unsigned InstCount = Record[3]; uint64_t RawFunFlags = 0; + uint64_t EntryCount = 0; unsigned NumRefs = Record[4]; unsigned NumImmutableRefs = 0; int RefListStartIndex = 5; if (Version >= 4) { RawFunFlags = Record[4]; - NumRefs = Record[5]; RefListStartIndex = 6; + size_t NumRefsIndex = 5; if (Version >= 5) { - NumImmutableRefs = Record[6]; RefListStartIndex = 7; + if (Version >= 6) { + NumRefsIndex = 6; + EntryCount = Record[5]; + RefListStartIndex = 8; + } + NumImmutableRefs = Record[RefListStartIndex - 1]; } + NumRefs = Record[NumRefsIndex]; } auto Flags = getDecodedGVSummaryFlags(RawFlags, Version); @@ -5464,8 +5471,8 @@ ValueInfo VI = getValueInfoFromValueId(ValueID).first; setImmutableRefs(Refs, NumImmutableRefs); auto FS = llvm::make_unique( - Flags, InstCount, getDecodedFFlags(RawFunFlags), std::move(Refs), - std::move(Edges), std::move(PendingTypeTests), + Flags, InstCount, getDecodedFFlags(RawFunFlags), EntryCount, + std::move(Refs), std::move(Edges), std::move(PendingTypeTests), std::move(PendingTypeTestAssumeVCalls), std::move(PendingTypeCheckedLoadVCalls), std::move(PendingTypeTestAssumeConstVCalls), Index: lib/Bitcode/Writer/BitcodeWriter.cpp =================================================================== --- lib/Bitcode/Writer/BitcodeWriter.cpp +++ lib/Bitcode/Writer/BitcodeWriter.cpp @@ -3601,7 +3601,7 @@ // Current version for the summary. // This is bumped whenever we introduce changes in the way some record are // interpreted, like flags for instance. -static const uint64_t INDEX_VERSION = 5; +static const uint64_t INDEX_VERSION = 6; /// Emit the per-module summary section alongside the rest of /// the module's bitcode. @@ -3747,6 +3747,7 @@ Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // flags Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // instcount Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // fflags + Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // entrycount Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // numrefs Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // immutablerefcnt // numrefs x valueid, n x (valueid) @@ -3861,6 +3862,8 @@ NameVals.push_back(getEncodedGVSummaryFlags(FS->flags())); NameVals.push_back(FS->instCount()); NameVals.push_back(getEncodedFFlags(FS->fflags())); + NameVals.push_back(FS->entryCount()); + // Fill in below NameVals.push_back(0); // numrefs NameVals.push_back(0); // immutablerefcnt @@ -3875,8 +3878,8 @@ ImmutableRefCnt++; Count++; } - NameVals[5] = Count; - NameVals[6] = ImmutableRefCnt; + NameVals[6] = Count; + NameVals[7] = ImmutableRefCnt; bool HasProfileData = false; for (auto &EI : FS->calls()) { Index: lib/LTO/LTO.cpp =================================================================== --- lib/LTO/LTO.cpp +++ lib/LTO/LTO.cpp @@ -42,6 +42,7 @@ #include "llvm/Target/TargetOptions.h" #include "llvm/Transforms/IPO.h" #include "llvm/Transforms/IPO/PassManagerBuilder.h" +#include "llvm/Transforms/Utils/FunctionImportUtils.h" #include "llvm/Transforms/Utils/SplitModule.h" #include @@ -1170,6 +1171,9 @@ if (!ModuleToDefinedGVSummaries.count(Mod.first)) ModuleToDefinedGVSummaries.try_emplace(Mod.first); + // Synthesize entry counts for functions in the CombinedIndex. + computeSyntheticCounts(ThinLTO.CombinedIndex); + StringMap ImportLists( ThinLTO.ModuleMap.size()); StringMap ExportLists( Index: lib/LTO/ThinLTOCodeGenerator.cpp =================================================================== --- lib/LTO/ThinLTOCodeGenerator.cpp +++ lib/LTO/ThinLTOCodeGenerator.cpp @@ -883,6 +883,9 @@ // Compute "dead" symbols, we don't want to import/export these! computeDeadSymbolsInIndex(*Index, GUIDPreservedSymbols); + // Synthesize entry counts for functions in the combined index. + computeSyntheticCounts(*Index); + // Collect the import/export lists for all modules from the call-graph in the // combined index. StringMap ImportLists(ModuleCount); Index: lib/Transforms/IPO/SyntheticCountsPropagation.cpp =================================================================== --- lib/Transforms/IPO/SyntheticCountsPropagation.cpp +++ lib/Transforms/IPO/SyntheticCountsPropagation.cpp @@ -45,11 +45,7 @@ #define DEBUG_TYPE "synthetic-counts-propagation" -/// Initial synthetic count assigned to functions. -static cl::opt - InitialSyntheticCount("initial-synthetic-count", cl::Hidden, cl::init(10), - cl::ZeroOrMore, - cl::desc("Initial value of synthetic entry count.")); +extern cl::opt InitialSyntheticCount; /// Initial synthetic count assigned to inline functions. static cl::opt InlineSyntheticCount( Index: lib/Transforms/Utils/FunctionImportUtils.cpp =================================================================== --- lib/Transforms/Utils/FunctionImportUtils.cpp +++ lib/Transforms/Utils/FunctionImportUtils.cpp @@ -13,9 +13,24 @@ //===----------------------------------------------------------------------===// #include "llvm/Transforms/Utils/FunctionImportUtils.h" +#include "llvm/Analysis/SyntheticCountsUtils.h" #include "llvm/IR/InstIterator.h" using namespace llvm; +cl::opt EnableImportEntryCount( + "enable-import-entry-count", cl::init(false), cl::Hidden, + cl::desc("Attach 'synthetic_entry_count' metadata after importing")); + +// FIXME: This should probably be moved to a separate file in Transforms/Utils. +// This is currently used both here and in +// Transforms/IPO/SyntheticCountsPropagation.cpp and is defined here because +// Transforms/Utils should not depend on Transforms/IPO +/// Initial synthetic count assigned to functions. +cl::opt + InitialSyntheticCount("initial-synthetic-count", cl::Hidden, cl::init(10), + cl::ZeroOrMore, + cl::desc("Initial value of synthetic entry count.")); + /// Checks if we should import SGV as a definition, otherwise import as a /// declaration. bool FunctionImportGlobalProcessing::doImportAsDefinition( @@ -203,11 +218,26 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) { - // Check the summaries to see if the symbol gets resolved to a known local - // definition. ValueInfo VI; if (GV.hasName()) { VI = ImportIndex.getValueInfo(GV.getGUID()); + // Set synthetic function entry counts. + if (VI && EnableImportEntryCount) { + if (Function *F = dyn_cast(&GV)) { + if (!F->isDeclaration()) { + for (auto &S : VI.getSummaryList()) { + FunctionSummary *FS = dyn_cast(S->getBaseObject()); + if (FS->modulePath() == M.getModuleIdentifier()) { + F->setEntryCount(Function::ProfileCount(FS->entryCount(), + Function::PCT_Synthetic)); + break; + } + } + } + } + } + // Check the summaries to see if the symbol gets resolved to a known local + // definition. if (VI && VI.isDSOLocal()) { GV.setDSOLocal(true); if (GV.hasDLLImportStorageClass()) @@ -278,3 +308,57 @@ FunctionImportGlobalProcessing ThinLTOProcessing(M, Index, GlobalsToImport); return ThinLTOProcessing.run(); } + +static void initializeCounts(ModuleSummaryIndex &Index) { + auto Root = Index.calculateCallGraphRoot(); + // Root is a fake node. All its successors are the actual roots of the + // callgraph. + // FIXME: This initializes the entry counts of only the root nodes. This makes + // sense when compiling a binary with ThinLTO, but for libraries any of the + // non-root nodes could be called from outside. + for (auto &C : Root.calls()) { + auto &V = C.first; + for (auto &GVS : V.getSummaryList()) { + auto S = GVS.get()->getBaseObject(); + auto *F = cast(S); + F->setEntryCount(InitialSyntheticCount); + } + } +} + +void llvm::computeSyntheticCounts(ModuleSummaryIndex &Index) { + if (!EnableImportEntryCount) + return; + + using Scaled64 = ScaledNumber; + initializeCounts(Index); + auto GetCallSiteRelFreq = [](FunctionSummary::EdgeTy &Edge) { + // FIXME: Handle fake/invalid edges? + return Scaled64(Edge.second.RelBlockFreq, -CalleeInfo::ScaleShift); + }; + auto GetEntryCount = [](ValueInfo V) { + if (V.getSummaryList().size()) { + auto S = V.getSummaryList().front().get()->getBaseObject(); + auto *F = cast(S); + return F->entryCount(); + } else { + return UINT64_C(0); + } + }; + auto AddToEntryCount = [](ValueInfo V, uint64_t New) { + if (!V.getSummaryList().size()) + return; + for (auto &GVS : V.getSummaryList()) { + auto S = GVS.get()->getBaseObject(); + auto *F = cast(S); + F->setEntryCount(SaturatingAdd(F->entryCount(), New)); + } + }; + + // After initializing the counts in initializeCounts above, the counts have to + // be propagated across the combined callgraph. + // SyntheticCountsUtils::propagate takes care of this propagation on any + // callgraph that specialized GraphTraits. + SyntheticCountsUtils::propagate( + &Index, GetCallSiteRelFreq, GetEntryCount, AddToEntryCount); +} Index: test/Bitcode/summary_version.ll =================================================================== --- test/Bitcode/summary_version.ll +++ test/Bitcode/summary_version.ll @@ -2,7 +2,7 @@ ; RUN: opt -module-summary %s -o - | llvm-bcanalyzer -dump | FileCheck %s ; CHECK: +; CHECK: Index: test/Bitcode/thinlto-alias.ll =================================================================== --- test/Bitcode/thinlto-alias.ll +++ test/Bitcode/thinlto-alias.ll @@ -33,7 +33,7 @@ ; COMBINED-NEXT: ; COMBINED-NEXT: -; COMBINED-NEXT: +; COMBINED-NEXT: ; COMBINED-NEXT: +; COMBINED-NEXT: ; COMBINED-NEXT: ; ModuleID = 'thinlto-function-summary-callgraph.ll' Index: test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll =================================================================== --- test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll +++ test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll @@ -71,7 +71,7 @@ ; COMBINED-NEXT: +; COMBINED-NEXT: ; COMBINED_NEXT: Index: test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll =================================================================== --- test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll +++ test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll @@ -58,7 +58,7 @@ ; COMBINED-NEXT: +; COMBINED-NEXT: ; COMBINED_NEXT: Index: test/Bitcode/thinlto-function-summary-callgraph.ll =================================================================== --- test/Bitcode/thinlto-function-summary-callgraph.ll +++ test/Bitcode/thinlto-function-summary-callgraph.ll @@ -33,7 +33,7 @@ ; COMBINED-NEXT: +; COMBINED-NEXT: ; COMBINED-NEXT: ; ModuleID = 'thinlto-function-summary-callgraph.ll' Index: test/ThinLTO/X86/Inputs/function_entry_count.ll =================================================================== --- /dev/null +++ test/ThinLTO/X86/Inputs/function_entry_count.ll @@ -0,0 +1,9 @@ +target triple = "x86_64-unknown-linux-gnu" +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" + +declare void @h(); + +define void @g() { + call void @h(); + ret void +} Index: test/ThinLTO/X86/function_entry_count.ll =================================================================== --- /dev/null +++ test/ThinLTO/X86/function_entry_count.ll @@ -0,0 +1,44 @@ +; RUN: opt -thinlto-bc %s -write-relbf-to-summary -thin-link-bitcode-file=%t1.thinlink.bc -o %t1.bc +; RUN: opt -thinlto-bc %p/Inputs/function_entry_count.ll -write-relbf-to-summary -thin-link-bitcode-file=%t2.thinlink.bc -o %t2.bc + +; First perform the thin link on the normal bitcode file. +; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t.o -save-temps -enable-import-entry-count \ +; RUN: -r=%t1.bc,g, \ +; RUN: -r=%t1.bc,f,px \ +; RUN: -r=%t1.bc,h,px \ +; RUN: -r=%t2.bc,h, \ +; RUN: -r=%t2.bc,g,px +; RUN: llvm-dis -o - %t.o.1.3.import.bc | FileCheck %s + +; RUN: llvm-lto -thinlto-action=run -enable-import-entry-count -exported-symbol=f \ +; RUN: -exported-symbol=g -exported-symbol=h -thinlto-save-temps=%t3. %t1.bc %t2.bc +; RUN: llvm-dis %t3.0.3.imported.bc -o - | FileCheck %s + +; CHECK: define void @h() !prof ![[PROF2:[0-9]+]] +; CHECK: define void @f(i32 %n) !prof ![[PROF1:[0-9]+]] +; CHECK: define available_externally void @g() !prof ![[PROF2]] +; CHECK-DAG: ![[PROF1]] = !{!"synthetic_function_entry_count", i64 10} +; CHECK-DAG: ![[PROF2]] = !{!"synthetic_function_entry_count", i64 198} + +target triple = "x86_64-unknown-linux-gnu" +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" + +declare void @g(); + +define void @h() { + ret void +} + +define void @f(i32 %n) { +entry: + %cmp = icmp slt i32 %n, 1 + br i1 %cmp, label %exit, label %loop +loop: + %n1 = phi i32 [%n, %entry], [%n2, %loop] + call void @g() + %n2 = sub i32 %n1, 1 + %cmp2 = icmp slt i32 %n, 1 + br i1 %cmp2, label %exit, label %loop +exit: + ret void +}