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//===- Inliner.cpp - Code common to all inliners --------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the mechanics required to implement inlining without
// missing any calls and updating the call graph. The decisions of which calls
// are profitable to inline are implemented elsewhere.
#include "llvm/Transforms/IPO/Inliner.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/CGSCCPassManager.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Analysis/InlineCost.h"
#include "llvm/Analysis/LazyCallGraph.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/ImportedFunctionsInliningStatistics.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
#include <algorithm>
#include <cassert>
#include <functional>
#include <sstream>
#include <tuple>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "inline"
STATISTIC(NumInlined, "Number of functions inlined");
STATISTIC(NumCallsDeleted, "Number of call sites deleted, not inlined");
STATISTIC(NumDeleted, "Number of functions deleted because all callers found");
STATISTIC(NumMergedAllocas, "Number of allocas merged together");
// This weirdly named statistic tracks the number of times that, when attempting
// to inline a function A into B, we analyze the callers of B in order to see
// if those would be more profitable and blocked inline steps.
STATISTIC(NumCallerCallersAnalyzed, "Number of caller-callers analyzed");
/// Flag to disable manual alloca merging.
/// Merging of allocas was originally done as a stack-size saving technique
/// prior to LLVM's code generator having support for stack coloring based on
/// lifetime markers. It is now in the process of being removed. To experiment
/// with disabling it and relying fully on lifetime marker based stack
/// coloring, you can pass this flag to LLVM.
static cl::opt<bool>
cl::init(false), cl::Hidden);
namespace {
enum class InlinerFunctionImportStatsOpts {
No = 0,
Basic = 1,
Verbose = 2,
} // end anonymous namespace
static cl::opt<InlinerFunctionImportStatsOpts> InlinerFunctionImportStats(
cl::values(clEnumValN(InlinerFunctionImportStatsOpts::Basic, "basic",
"basic statistics"),
clEnumValN(InlinerFunctionImportStatsOpts::Verbose, "verbose",
"printing of statistics for each inlined function")),
cl::Hidden, cl::desc("Enable inliner stats for imported functions"));
/// Flag to add inline messages as callsite attributes 'inline-remark'.
static cl::opt<bool>
InlineRemarkAttribute("inline-remark-attribute", cl::init(false),
cl::desc("Enable adding inline-remark attribute to"
" callsites processed by inliner but decided"
" to be not inlined"));
LegacyInlinerBase::LegacyInlinerBase(char &ID) : CallGraphSCCPass(ID) {}
LegacyInlinerBase::LegacyInlinerBase(char &ID, bool InsertLifetime)
: CallGraphSCCPass(ID), InsertLifetime(InsertLifetime) {}
/// For this class, we declare that we require and preserve the call graph.
/// If the derived class implements this method, it should
/// always explicitly call the implementation here.
void LegacyInlinerBase::getAnalysisUsage(AnalysisUsage &AU) const {
using InlinedArrayAllocasTy = DenseMap<ArrayType *, std::vector<AllocaInst *>>;
/// Look at all of the allocas that we inlined through this call site. If we
/// have already inlined other allocas through other calls into this function,
/// then we know that they have disjoint lifetimes and that we can merge them.
/// There are many heuristics possible for merging these allocas, and the
/// different options have different tradeoffs. One thing that we *really*
/// don't want to hurt is SRoA: once inlining happens, often allocas are no
/// longer address taken and so they can be promoted.
/// Our "solution" for that is to only merge allocas whose outermost type is an
/// array type. These are usually not promoted because someone is using a
/// variable index into them. These are also often the most important ones to
/// merge.
/// A better solution would be to have real memory lifetime markers in the IR
/// and not have the inliner do any merging of allocas at all. This would
/// allow the backend to do proper stack slot coloring of all allocas that
/// *actually make it to the backend*, which is really what we want.
/// Because we don't have this information, we do this simple and useful hack.
static void mergeInlinedArrayAllocas(
Function *Caller, InlineFunctionInfo &IFI,
InlinedArrayAllocasTy &InlinedArrayAllocas, int InlineHistory) {
SmallPtrSet<AllocaInst *, 16> UsedAllocas;
// When processing our SCC, check to see if CS was inlined from some other
// call site. For example, if we're processing "A" in this code:
// A() { B() }
// B() { x = alloca ... C() }
// C() { y = alloca ... }
// Assume that C was not inlined into B initially, and so we're processing A
// and decide to inline B into A. Doing this makes an alloca available for
// reuse and makes a callsite (C) available for inlining. When we process
// the C call site we don't want to do any alloca merging between X and Y
// because their scopes are not disjoint. We could make this smarter by
// keeping track of the inline history for each alloca in the
// InlinedArrayAllocas but this isn't likely to be a significant win.
if (InlineHistory != -1) // Only do merging for top-level call sites in SCC.
// Loop over all the allocas we have so far and see if they can be merged with
// a previously inlined alloca. If not, remember that we had it.
for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size(); AllocaNo != e;
++AllocaNo) {
AllocaInst *AI = IFI.StaticAllocas[AllocaNo];
// Don't bother trying to merge array allocations (they will usually be
// canonicalized to be an allocation *of* an array), or allocations whose
// type is not itself an array (because we're afraid of pessimizing SRoA).
ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType());
if (!ATy || AI->isArrayAllocation())
// Get the list of all available allocas for this array type.
std::vector<AllocaInst *> &AllocasForType = InlinedArrayAllocas[ATy];
// Loop over the allocas in AllocasForType to see if we can reuse one. Note
// that we have to be careful not to reuse the same "available" alloca for
// multiple different allocas that we just inlined, we use the 'UsedAllocas'
// set to keep track of which "available" allocas are being used by this
// function. Also, AllocasForType can be empty of course!
bool MergedAwayAlloca = false;
for (AllocaInst *AvailableAlloca : AllocasForType) {
unsigned Align1 = AI->getAlignment(),
Align2 = AvailableAlloca->getAlignment();
// The available alloca has to be in the right function, not in some other
// function in this SCC.
if (AvailableAlloca->getParent() != AI->getParent())
// If the inlined function already uses this alloca then we can't reuse
// it.
if (!UsedAllocas.insert(AvailableAlloca).second)
// Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare
// success!
LLVM_DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI
<< "\n\t\tINTO: " << *AvailableAlloca << '\n');
// Move affected dbg.declare calls immediately after the new alloca to
// avoid the situation when a dbg.declare precedes its alloca.
if (auto *L = LocalAsMetadata::getIfExists(AI))
if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L))
for (User *U : MDV->users())
if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
if (Align1 != Align2) {
if (!Align1 || !Align2) {
const DataLayout &DL = Caller->getParent()->getDataLayout();
unsigned TypeAlign = DL.getABITypeAlignment(AI->getAllocatedType());
Align1 = Align1 ? Align1 : TypeAlign;
Align2 = Align2 ? Align2 : TypeAlign;
if (Align1 > Align2)
MergedAwayAlloca = true;
IFI.StaticAllocas[AllocaNo] = nullptr;
// If we already nuked the alloca, we're done with it.
if (MergedAwayAlloca)
// If we were unable to merge away the alloca either because there are no
// allocas of the right type available or because we reused them all
// already, remember that this alloca came from an inlined function and mark
// it used so we don't reuse it for other allocas from this inline
// operation.
/// If it is possible to inline the specified call site,
/// do so and update the CallGraph for this operation.
/// This function also does some basic book-keeping to update the IR. The
/// InlinedArrayAllocas map keeps track of any allocas that are already
/// available from other functions inlined into the caller. If we are able to
/// inline this call site we attempt to reuse already available allocas or add
/// any new allocas to the set if not possible.
static InlineResult InlineCallIfPossible(
CallSite CS, InlineFunctionInfo &IFI,
InlinedArrayAllocasTy &InlinedArrayAllocas, int InlineHistory,
bool InsertLifetime, function_ref<AAResults &(Function &)> &AARGetter,
ImportedFunctionsInliningStatistics &ImportedFunctionsStats) {
Function *Callee = CS.getCalledFunction();
Function *Caller = CS.getCaller();
AAResults &AAR = AARGetter(*Callee);
// Try to inline the function. Get the list of static allocas that were
// inlined.
InlineResult IR = InlineFunction(CS, IFI, &AAR, InsertLifetime);
if (!IR)
return IR;
if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
ImportedFunctionsStats.recordInline(*Caller, *Callee);
AttributeFuncs::mergeAttributesForInlining(*Caller, *Callee);
if (!DisableInlinedAllocaMerging)
mergeInlinedArrayAllocas(Caller, IFI, InlinedArrayAllocas, InlineHistory);
return IR; // success
/// Return true if inlining of CS can block the caller from being
/// inlined which is proved to be more beneficial. \p IC is the
/// estimated inline cost associated with callsite \p CS.
/// \p TotalSecondaryCost will be set to the estimated cost of inlining the
/// caller if \p CS is suppressed for inlining.
static bool
shouldBeDeferred(Function *Caller, CallSite CS, InlineCost IC,
int &TotalSecondaryCost,
function_ref<InlineCost(CallSite CS)> GetInlineCost) {
// For now we only handle local or inline functions.
if (!Caller->hasLocalLinkage() && !Caller->hasLinkOnceODRLinkage())
return false;
// If the cost of inlining CS is non-positive, it is not going to prevent the
// caller from being inlined into its callers and hence we don't need to
// defer.
if (IC.getCost() <= 0)
return false;
// Try to detect the case where the current inlining candidate caller (call
// it B) is a static or linkonce-ODR function and is an inlining candidate
// elsewhere, and the current candidate callee (call it C) is large enough
// that inlining it into B would make B too big to inline later. In these
// circumstances it may be best not to inline C into B, but to inline B into
// its callers.
// This only applies to static and linkonce-ODR functions because those are
// expected to be available for inlining in the translation units where they
// are used. Thus we will always have the opportunity to make local inlining
// decisions. Importantly the linkonce-ODR linkage covers inline functions
// and templates in C++.
// FIXME: All of this logic should be sunk into getInlineCost. It relies on
// the internal implementation of the inline cost metrics rather than
// treating them as truly abstract units etc.
TotalSecondaryCost = 0;
// The candidate cost to be imposed upon the current function.
int CandidateCost = IC.getCost() - 1;
// If the caller has local linkage and can be inlined to all its callers, we
// can apply a huge negative bonus to TotalSecondaryCost.
bool ApplyLastCallBonus = Caller->hasLocalLinkage() && !Caller->hasOneUse();
// This bool tracks what happens if we DO inline C into B.
bool inliningPreventsSomeOuterInline = false;
for (User *U : Caller->users()) {
// If the caller will not be removed (either because it does not have a
// local linkage or because the LastCallToStaticBonus has been already
// applied), then we can exit the loop early.
if (!ApplyLastCallBonus && TotalSecondaryCost >= IC.getCost())
return false;
CallSite CS2(U);
// If this isn't a call to Caller (it could be some other sort
// of reference) skip it. Such references will prevent the caller
// from being removed.
if (!CS2 || CS2.getCalledFunction() != Caller) {
ApplyLastCallBonus = false;
InlineCost IC2 = GetInlineCost(CS2);
if (!IC2) {
ApplyLastCallBonus = false;
if (IC2.isAlways())
// See if inlining of the original callsite would erase the cost delta of
// this callsite. We subtract off the penalty for the call instruction,
// which we would be deleting.
if (IC2.getCostDelta() <= CandidateCost) {
inliningPreventsSomeOuterInline = true;
TotalSecondaryCost += IC2.getCost();
// If all outer calls to Caller would get inlined, the cost for the last
// one is set very low by getInlineCost, in anticipation that Caller will
// be removed entirely. We did not account for this above unless there
// is only one caller of Caller.
if (ApplyLastCallBonus)
TotalSecondaryCost -= InlineConstants::LastCallToStaticBonus;
if (inliningPreventsSomeOuterInline && TotalSecondaryCost < IC.getCost())
return true;
return false;
static std::basic_ostream<char> &operator<<(std::basic_ostream<char> &R,
const ore::NV &Arg) {
return R << Arg.Val;
template <class RemarkT>
RemarkT &operator<<(RemarkT &&R, const InlineCost &IC) {
using namespace ore;
if (IC.isAlways()) {
R << "(cost=always)";
} else if (IC.isNever()) {
R << "(cost=never)";
} else {
R << "(cost=" << ore::NV("Cost", IC.getCost())
<< ", threshold=" << ore::NV("Threshold", IC.getThreshold()) << ")";
if (const char *Reason = IC.getReason())
R << ": " << ore::NV("Reason", Reason);
return R;
static std::string inlineCostStr(const InlineCost &IC) {
std::stringstream Remark;
Remark << IC;
return Remark.str();
/// Return the cost only if the inliner should attempt to inline at the given
/// CallSite. If we return the cost, we will emit an optimisation remark later
/// using that cost, so we won't do so from this function.
static Optional<InlineCost>
shouldInline(CallSite CS, function_ref<InlineCost(CallSite CS)> GetInlineCost,
OptimizationRemarkEmitter &ORE) {
using namespace ore;
InlineCost IC = GetInlineCost(CS);
Instruction *Call = CS.getInstruction();
Function *Callee = CS.getCalledFunction();
Function *Caller = CS.getCaller();
if (IC.isAlways()) {
LLVM_DEBUG(dbgs() << " Inlining " << inlineCostStr(IC)
<< ", Call: " << *CS.getInstruction() << "\n");
return IC;
if (IC.isNever()) {
LLVM_DEBUG(dbgs() << " NOT Inlining " << inlineCostStr(IC)
<< ", Call: " << *CS.getInstruction() << "\n");
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NeverInline", Call)
<< NV("Callee", Callee) << " not inlined into "
<< NV("Caller", Caller) << " because it should never be inlined "
<< IC;
return IC;
if (!IC) {
LLVM_DEBUG(dbgs() << " NOT Inlining " << inlineCostStr(IC)
<< ", Call: " << *CS.getInstruction() << "\n");
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "TooCostly", Call)
<< NV("Callee", Callee) << " not inlined into "
<< NV("Caller", Caller) << " because too costly to inline " << IC;
return IC;
int TotalSecondaryCost = 0;
if (shouldBeDeferred(Caller, CS, IC, TotalSecondaryCost, GetInlineCost)) {
LLVM_DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction()
<< " Cost = " << IC.getCost()
<< ", outer Cost = " << TotalSecondaryCost << '\n');
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "IncreaseCostInOtherContexts",
<< "Not inlining. Cost of inlining " << NV("Callee", Callee)
<< " increases the cost of inlining " << NV("Caller", Caller)
<< " in other contexts";
// IC does not bool() to false, so get an InlineCost that will.
// This will not be inspected to make an error message.
return None;
LLVM_DEBUG(dbgs() << " Inlining " << inlineCostStr(IC)
<< ", Call: " << *CS.getInstruction() << '\n');
return IC;
/// Return true if the specified inline history ID
/// indicates an inline history that includes the specified function.
static bool InlineHistoryIncludes(
Function *F, int InlineHistoryID,
const SmallVectorImpl<std::pair<Function *, int>> &InlineHistory) {
while (InlineHistoryID != -1) {
assert(unsigned(InlineHistoryID) < InlineHistory.size() &&
"Invalid inline history ID");
if (InlineHistory[InlineHistoryID].first == F)
return true;
InlineHistoryID = InlineHistory[InlineHistoryID].second;
return false;
bool LegacyInlinerBase::doInitialization(CallGraph &CG) {
if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
return false; // No changes to CallGraph.
bool LegacyInlinerBase::runOnSCC(CallGraphSCC &SCC) {
if (skipSCC(SCC))
return false;
return inlineCalls(SCC);
static void emit_inlined_into(OptimizationRemarkEmitter &ORE, DebugLoc &DLoc,
const BasicBlock *Block, const Function &Callee,
const Function &Caller, const InlineCost &IC) {
ORE.emit([&]() {
bool AlwaysInline = IC.isAlways();
StringRef RemarkName = AlwaysInline ? "AlwaysInline" : "Inlined";
return OptimizationRemark(DEBUG_TYPE, RemarkName, DLoc, Block)
<< ore::NV("Callee", &Callee) << " inlined into "
<< ore::NV("Caller", &Caller) << " with " << IC;
static void setInlineRemark(CallSite &CS, StringRef message) {
if (!InlineRemarkAttribute)
Attribute attr = Attribute::get(CS->getContext(), "inline-remark", message);
CS.addAttribute(AttributeList::FunctionIndex, attr);
static bool
inlineCallsImpl(CallGraphSCC &SCC, CallGraph &CG,
std::function<AssumptionCache &(Function &)> GetAssumptionCache,
ProfileSummaryInfo *PSI,
std::function<TargetLibraryInfo &(Function &)> GetTLI,
bool InsertLifetime,
function_ref<InlineCost(CallSite CS)> GetInlineCost,
function_ref<AAResults &(Function &)> AARGetter,
ImportedFunctionsInliningStatistics &ImportedFunctionsStats) {
SmallPtrSet<Function *, 8> SCCFunctions;
LLVM_DEBUG(dbgs() << "Inliner visiting SCC:");
for (CallGraphNode *Node : SCC) {
Function *F = Node->getFunction();
if (F)
LLVM_DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE"));
// Scan through and identify all call sites ahead of time so that we only
// inline call sites in the original functions, not call sites that result
// from inlining other functions.
SmallVector<std::pair<CallSite, int>, 16> CallSites;
// When inlining a callee produces new call sites, we want to keep track of
// the fact that they were inlined from the callee. This allows us to avoid
// infinite inlining in some obscure cases. To represent this, we use an
// index into the InlineHistory vector.
SmallVector<std::pair<Function *, int>, 8> InlineHistory;
for (CallGraphNode *Node : SCC) {
Function *F = Node->getFunction();
if (!F || F->isDeclaration())
OptimizationRemarkEmitter ORE(F);
for (BasicBlock &BB : *F)
for (Instruction &I : BB) {
CallSite CS(cast<Value>(&I));
// If this isn't a call, or it is a call to an intrinsic, it can
// never be inlined.
if (!CS || isa<IntrinsicInst>(I))
// If this is a direct call to an external function, we can never inline
// it. If it is an indirect call, inlining may resolve it to be a
// direct call, so we keep it.
if (Function *Callee = CS.getCalledFunction())
if (Callee->isDeclaration()) {
using namespace ore;
setInlineRemark(CS, "unavailable definition");
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
<< NV("Callee", Callee) << " will not be inlined into "
<< NV("Caller", CS.getCaller())
<< " because its definition is unavailable"
<< setIsVerbose();
CallSites.push_back(std::make_pair(CS, -1));
LLVM_DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n");
// If there are no calls in this function, exit early.
if (CallSites.empty())
return false;
// Now that we have all of the call sites, move the ones to functions in the
// current SCC to the end of the list.
unsigned FirstCallInSCC = CallSites.size();
for (unsigned i = 0; i < FirstCallInSCC; ++i)
if (Function *F = CallSites[i].first.getCalledFunction())
if (SCCFunctions.count(F))
std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
InlinedArrayAllocasTy InlinedArrayAllocas;
InlineFunctionInfo InlineInfo(&CG, &GetAssumptionCache, PSI);
// Now that we have all of the call sites, loop over them and inline them if
// it looks profitable to do so.
bool Changed = false;
bool LocalChange;
do {
LocalChange = false;
// Iterate over the outer loop because inlining functions can cause indirect
// calls to become direct calls.
// CallSites may be modified inside so ranged for loop can not be used.
for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
CallSite CS = CallSites[CSi].first;
Function *Caller = CS.getCaller();
Function *Callee = CS.getCalledFunction();
// We can only inline direct calls to non-declarations.
if (!Callee || Callee->isDeclaration())
Instruction *Instr = CS.getInstruction();
bool IsTriviallyDead =
isInstructionTriviallyDead(Instr, &GetTLI(*Caller));
int InlineHistoryID;
if (!IsTriviallyDead) {
// If this call site was obtained by inlining another function, verify
// that the include path for the function did not include the callee
// itself. If so, we'd be recursively inlining the same function,
// which would provide the same callsites, which would cause us to
// infinitely inline.
InlineHistoryID = CallSites[CSi].second;
if (InlineHistoryID != -1 &&
InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) {
setInlineRemark(CS, "recursive");
// FIXME for new PM: because of the old PM we currently generate ORE and
// in turn BFI on demand. With the new PM, the ORE dependency should
// just become a regular analysis dependency.
OptimizationRemarkEmitter ORE(Caller);
Optional<InlineCost> OIC = shouldInline(CS, GetInlineCost, ORE);
// If the policy determines that we should inline this function,
// delete the call instead.
if (!OIC.hasValue()) {
setInlineRemark(CS, "deferred");
if (!OIC.getValue()) {
// shouldInline() call returned a negative inline cost that explains
// why this callsite should not be inlined.
setInlineRemark(CS, inlineCostStr(*OIC));
// If this call site is dead and it is to a readonly function, we should
// just delete the call instead of trying to inline it, regardless of
// size. This happens because IPSCCP propagates the result out of the
// call and then we're left with the dead call.
if (IsTriviallyDead) {
LLVM_DEBUG(dbgs() << " -> Deleting dead call: " << *Instr << "\n");
// Update the call graph by deleting the edge from Callee to Caller.
setInlineRemark(CS, "trivially dead");
} else {
// Get DebugLoc to report. CS will be invalid after Inliner.
DebugLoc DLoc = CS->getDebugLoc();
BasicBlock *Block = CS.getParent();
// Attempt to inline the function.
using namespace ore;
InlineResult IR = InlineCallIfPossible(
CS, InlineInfo, InlinedArrayAllocas, InlineHistoryID,
InsertLifetime, AARGetter, ImportedFunctionsStats);
if (!IR) {
setInlineRemark(CS, std::string(IR) + "; " + inlineCostStr(*OIC));
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc,
<< NV("Callee", Callee) << " will not be inlined into "
<< NV("Caller", Caller) << ": " << NV("Reason", IR.message);
emit_inlined_into(ORE, DLoc, Block, *Callee, *Caller, *OIC);
// If inlining this function gave us any new call sites, throw them
// onto our worklist to process. They are useful inline candidates.
if (!InlineInfo.InlinedCalls.empty()) {
// Create a new inline history entry for this, so that we remember
// that these new callsites came about due to inlining Callee.
int NewHistoryID = InlineHistory.size();
InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID));
for (Value *Ptr : InlineInfo.InlinedCalls)
CallSites.push_back(std::make_pair(CallSite(Ptr), NewHistoryID));
// If we inlined or deleted the last possible call site to the function,
// delete the function body now.
if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() &&
// TODO: Can remove if in SCC now.
!SCCFunctions.count(Callee) &&
// The function may be apparently dead, but if there are indirect
// callgraph references to the node, we cannot delete it yet, this
// could invalidate the CGSCC iterator.
CG[Callee]->getNumReferences() == 0) {
LLVM_DEBUG(dbgs() << " -> Deleting dead function: "
<< Callee->getName() << "\n");
CallGraphNode *CalleeNode = CG[Callee];
// Remove any call graph edges from the callee to its callees.
// Removing the node for callee from the call graph and delete it.
delete CG.removeFunctionFromModule(CalleeNode);
// Remove this call site from the list. If possible, use
// swap/pop_back for efficiency, but do not use it if doing so would
// move a call site to a function in this SCC before the
// 'FirstCallInSCC' barrier.
if (SCC.isSingular()) {
CallSites[CSi] = CallSites.back();
} else {
CallSites.erase(CallSites.begin() + CSi);
Changed = true;
LocalChange = true;
} while (LocalChange);
return Changed;
bool LegacyInlinerBase::inlineCalls(CallGraphSCC &SCC) {
CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
ACT = &getAnalysis<AssumptionCacheTracker>();
PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
auto GetTLI = [&](Function &F) -> TargetLibraryInfo & {
return getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
return ACT->getAssumptionCache(F);
return inlineCallsImpl(
SCC, CG, GetAssumptionCache, PSI, GetTLI, InsertLifetime,
[this](CallSite CS) { return getInlineCost(CS); }, LegacyAARGetter(*this),
/// Remove now-dead linkonce functions at the end of
/// processing to avoid breaking the SCC traversal.
bool LegacyInlinerBase::doFinalization(CallGraph &CG) {
if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
ImportedFunctionsStats.dump(InlinerFunctionImportStats ==
return removeDeadFunctions(CG);
/// Remove dead functions that are not included in DNR (Do Not Remove) list.
bool LegacyInlinerBase::removeDeadFunctions(CallGraph &CG,
bool AlwaysInlineOnly) {
SmallVector<CallGraphNode *, 16> FunctionsToRemove;
SmallVector<Function *, 16> DeadFunctionsInComdats;
auto RemoveCGN = [&](CallGraphNode *CGN) {
// Remove any call graph edges from the function to its callees.
// Remove any edges from the external node to the function's call graph
// node. These edges might have been made irrelegant due to
// optimization of the program.
// Removing the node for callee from the call graph and delete it.
// Scan for all of the functions, looking for ones that should now be removed
// from the program. Insert the dead ones in the FunctionsToRemove set.
for (const auto &I : CG) {
CallGraphNode *CGN = I.second.get();
Function *F = CGN->getFunction();
if (!F || F->isDeclaration())
// Handle the case when this function is called and we only want to care
// about always-inline functions. This is a bit of a hack to share code
// between here and the InlineAlways pass.
if (AlwaysInlineOnly && !F->hasFnAttribute(Attribute::AlwaysInline))
// If the only remaining users of the function are dead constants, remove
// them.
if (!F->isDefTriviallyDead())
// It is unsafe to drop a function with discardable linkage from a COMDAT
// without also dropping the other members of the COMDAT.
// The inliner doesn't visit non-function entities which are in COMDAT
// groups so it is unsafe to do so *unless* the linkage is local.
if (!F->hasLocalLinkage()) {
if (F->hasComdat()) {
if (!DeadFunctionsInComdats.empty()) {
// Filter out the functions whose comdats remain alive.
filterDeadComdatFunctions(CG.getModule(), DeadFunctionsInComdats);
// Remove the rest.
for (Function *F : DeadFunctionsInComdats)
if (FunctionsToRemove.empty())
return false;
// Now that we know which functions to delete, do so. We didn't want to do
// this inline, because that would invalidate our CallGraph::iterator
// objects. :(
// Note that it doesn't matter that we are iterating over a non-stable order
// here to do this, it doesn't matter which order the functions are deleted
// in.
array_pod_sort(FunctionsToRemove.begin(), FunctionsToRemove.end());
std::unique(FunctionsToRemove.begin(), FunctionsToRemove.end()),
for (CallGraphNode *CGN : FunctionsToRemove) {
delete CG.removeFunctionFromModule(CGN);
return true;
InlinerPass::~InlinerPass() {
if (ImportedFunctionsStats) {
assert(InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No);
ImportedFunctionsStats->dump(InlinerFunctionImportStats ==
PreservedAnalyses InlinerPass::run(LazyCallGraph::SCC &InitialC,
CGSCCAnalysisManager &AM, LazyCallGraph &CG,
CGSCCUpdateResult &UR) {
const ModuleAnalysisManager &MAM =
AM.getResult<ModuleAnalysisManagerCGSCCProxy>(InitialC, CG).getManager();
bool Changed = false;
assert(InitialC.size() > 0 && "Cannot handle an empty SCC!");
Module &M = *InitialC.begin()->getFunction().getParent();
ProfileSummaryInfo *PSI = MAM.getCachedResult<ProfileSummaryAnalysis>(M);
if (!ImportedFunctionsStats &&
InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No) {
ImportedFunctionsStats =
// We use a single common worklist for calls across the entire SCC. We
// process these in-order and append new calls introduced during inlining to
// the end.
// Note that this particular order of processing is actually critical to
// avoid very bad behaviors. Consider *highly connected* call graphs where
// each function contains a small amonut of code and a couple of calls to
// other functions. Because the LLVM inliner is fundamentally a bottom-up
// inliner, it can handle gracefully the fact that these all appear to be
// reasonable inlining candidates as it will flatten things until they become
// too big to inline, and then move on and flatten another batch.
// However, when processing call edges *within* an SCC we cannot rely on this
// bottom-up behavior. As a consequence, with heavily connected *SCCs* of
// functions we can end up incrementally inlining N calls into each of
// N functions because each incremental inlining decision looks good and we
// don't have a topological ordering to prevent explosions.
// To compensate for this, we don't process transitive edges made immediate
// by inlining until we've done one pass of inlining across the entire SCC.
// Large, highly connected SCCs still lead to some amount of code bloat in
// this model, but it is uniformly spread across all the functions in the SCC
// and eventually they all become too large to inline, rather than
// incrementally maknig a single function grow in a super linear fashion.
SmallVector<std::pair<CallSite, int>, 16> Calls;
FunctionAnalysisManager &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(InitialC, CG)
// Populate the initial list of calls in this SCC.
for (auto &N : InitialC) {
auto &ORE =
// We want to generally process call sites top-down in order for
// simplifications stemming from replacing the call with the returned value
// after inlining to be visible to subsequent inlining decisions.
// FIXME: Using instructions sequence is a really bad way to do this.
// Instead we should do an actual RPO walk of the function body.
for (Instruction &I : instructions(N.getFunction()))
if (auto CS = CallSite(&I))
if (Function *Callee = CS.getCalledFunction()) {
if (!Callee->isDeclaration())
Calls.push_back({CS, -1});
else if (!isa<IntrinsicInst>(I)) {
using namespace ore;
setInlineRemark(CS, "unavailable definition");
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
<< NV("Callee", Callee) << " will not be inlined into "
<< NV("Caller", CS.getCaller())
<< " because its definition is unavailable"
<< setIsVerbose();
if (Calls.empty())
return PreservedAnalyses::all();
// Capture updatable variables for the current SCC and RefSCC.
auto *C = &InitialC;
auto *RC = &C->getOuterRefSCC();
// When inlining a callee produces new call sites, we want to keep track of
// the fact that they were inlined from the callee. This allows us to avoid
// infinite inlining in some obscure cases. To represent this, we use an
// index into the InlineHistory vector.
SmallVector<std::pair<Function *, int>, 16> InlineHistory;
// Track a set vector of inlined callees so that we can augment the caller
// with all of their edges in the call graph before pruning out the ones that
// got simplified away.
SmallSetVector<Function *, 4> InlinedCallees;
// Track the dead functions to delete once finished with inlining calls. We
// defer deleting these to make it easier to handle the call graph updates.
SmallVector<Function *, 4> DeadFunctions;
// Loop forward over all of the calls. Note that we cannot cache the size as
// inlining can introduce new calls that need to be processed.
for (int i = 0; i < (int)Calls.size(); ++i) {
// We expect the calls to typically be batched with sequences of calls that
// have the same caller, so we first set up some shared infrastructure for
// this caller. We also do any pruning we can at this layer on the caller
// alone.
Function &F = *Calls[i].first.getCaller();
LazyCallGraph::Node &N = *CG.lookup(F);
if (CG.lookupSCC(N) != C)
if (F.hasOptNone()) {
setInlineRemark(Calls[i].first, "optnone attribute");
LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n");
// Get a FunctionAnalysisManager via a proxy for this particular node. We
// do this each time we visit a node as the SCC may have changed and as
// we're going to mutate this particular function we want to make sure the
// proxy is in place to forward any invalidation events. We can use the
// manager we get here for looking up results for functions other than this
// node however because those functions aren't going to be mutated by this
// pass.
FunctionAnalysisManager &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(*C, CG)
// Get the remarks emission analysis for the caller.
auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
std::function<AssumptionCache &(Function &)> GetAssumptionCache =
[&](Function &F) -> AssumptionCache & {
return FAM.getResult<AssumptionAnalysis>(F);
auto GetBFI = [&](Function &F) -> BlockFrequencyInfo & {
return FAM.getResult<BlockFrequencyAnalysis>(F);
auto GetInlineCost = [&](CallSite CS) {
Function &Callee = *CS.getCalledFunction();
auto &CalleeTTI = FAM.getResult<TargetIRAnalysis>(Callee);
bool RemarksEnabled =
return getInlineCost(cast<CallBase>(*CS.getInstruction()), Params,
CalleeTTI, GetAssumptionCache, {GetBFI}, PSI,
RemarksEnabled ? &ORE : nullptr);
// Now process as many calls as we have within this caller in the sequnece.
// We bail out as soon as the caller has to change so we can update the
// call graph and prepare the context of that new caller.
bool DidInline = false;
for (; i < (int)Calls.size() && Calls[i].first.getCaller() == &F; ++i) {
int InlineHistoryID;
CallSite CS;
std::tie(CS, InlineHistoryID) = Calls[i];
Function &Callee = *CS.getCalledFunction();
if (InlineHistoryID != -1 &&
InlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory)) {
setInlineRemark(CS, "recursive");
// Check if this inlining may repeat breaking an SCC apart that has
// already been split once before. In that case, inlining here may
// trigger infinite inlining, much like is prevented within the inliner
// itself by the InlineHistory above, but spread across CGSCC iterations
// and thus hidden from the full inline history.
if (CG.lookupSCC(*CG.lookup(Callee)) == C &&
UR.InlinedInternalEdges.count({&N, C})) {
LLVM_DEBUG(dbgs() << "Skipping inlining internal SCC edge from a node "
"previously split out of this SCC by inlining: "
<< F.getName() << " -> " << Callee.getName() << "\n");
setInlineRemark(CS, "recursive SCC split");
Optional<InlineCost> OIC = shouldInline(CS, GetInlineCost, ORE);
// Check whether we want to inline this callsite.
if (!OIC.hasValue()) {
setInlineRemark(CS, "deferred");
if (!OIC.getValue()) {
// shouldInline() call returned a negative inline cost that explains
// why this callsite should not be inlined.
setInlineRemark(CS, inlineCostStr(*OIC));
// Setup the data structure used to plumb customization into the
// `InlineFunction` routine.
InlineFunctionInfo IFI(
/*cg=*/nullptr, &GetAssumptionCache, PSI,
// Get DebugLoc to report. CS will be invalid after Inliner.
DebugLoc DLoc = CS->getDebugLoc();
BasicBlock *Block = CS.getParent();
using namespace ore;
InlineResult IR = InlineFunction(CS, IFI);
if (!IR) {
setInlineRemark(CS, std::string(IR) + "; " + inlineCostStr(*OIC));
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc, Block)
<< NV("Callee", &Callee) << " will not be inlined into "
<< NV("Caller", &F) << ": " << NV("Reason", IR.message);
DidInline = true;
emit_inlined_into(ORE, DLoc, Block, Callee, F, *OIC);
// Add any new callsites to defined functions to the worklist.
if (!IFI.InlinedCallSites.empty()) {
int NewHistoryID = InlineHistory.size();
InlineHistory.push_back({&Callee, InlineHistoryID});
for (CallSite &CS : reverse(IFI.InlinedCallSites))
if (Function *NewCallee = CS.getCalledFunction())
if (!NewCallee->isDeclaration())
Calls.push_back({CS, NewHistoryID});
if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
ImportedFunctionsStats->recordInline(F, Callee);
// Merge the attributes based on the inlining.
AttributeFuncs::mergeAttributesForInlining(F, Callee);
// For local functions, check whether this makes the callee trivially
// dead. In that case, we can drop the body of the function eagerly
// which may reduce the number of callers of other functions to one,
// changing inline cost thresholds.
if (Callee.hasLocalLinkage()) {
// To check this we also need to nuke any dead constant uses (perhaps
// made dead by this operation on other functions).
if (Callee.use_empty() && !CG.isLibFunction(Callee)) {
std::remove_if(Calls.begin() + i + 1, Calls.end(),
[&Callee](const std::pair<CallSite, int> &Call) {
return Call.first.getCaller() == &Callee;
// Clear the body and queue the function itself for deletion when we
// finish inlining and call graph updates.
// Note that after this point, it is an error to do anything other
// than use the callee's address or delete it.
assert(find(DeadFunctions, &Callee) == DeadFunctions.end() &&
"Cannot put cause a function to become dead twice!");
// Back the call index up by one to put us in a good position to go around
// the outer loop.
if (!DidInline)
Changed = true;
// Add all the inlined callees' edges as ref edges to the caller. These are
// by definition trivial edges as we always have *some* transitive ref edge
// chain. While in some cases these edges are direct calls inside the
// callee, they have to be modeled in the inliner as reference edges as
// there may be a reference edge anywhere along the chain from the current
// caller to the callee that causes the whole thing to appear like
// a (transitive) reference edge that will require promotion to a call edge
// below.
for (Function *InlinedCallee : InlinedCallees) {
LazyCallGraph::Node &CalleeN = *CG.lookup(*InlinedCallee);
for (LazyCallGraph::Edge &E : *CalleeN)
RC->insertTrivialRefEdge(N, E.getNode());
// At this point, since we have made changes we have at least removed
// a call instruction. However, in the process we do some incremental
// simplification of the surrounding code. This simplification can
// essentially do all of the same things as a function pass and we can
// re-use the exact same logic for updating the call graph to reflect the
// change.
LazyCallGraph::SCC *OldC = C;
C = &updateCGAndAnalysisManagerForFunctionPass(CG, *C, N, AM, UR);
LLVM_DEBUG(dbgs() << "Updated inlining SCC: " << *C << "\n");
RC = &C->getOuterRefSCC();
// If this causes an SCC to split apart into multiple smaller SCCs, there
// is a subtle risk we need to prepare for. Other transformations may
// expose an "infinite inlining" opportunity later, and because of the SCC
// mutation, we will revisit this function and potentially re-inline. If we
// do, and that re-inlining also has the potentially to mutate the SCC
// structure, the infinite inlining problem can manifest through infinite
// SCC splits and merges. To avoid this, we capture the originating caller
// node and the SCC containing the call edge. This is a slight over
// approximation of the possible inlining decisions that must be avoided,
// but is relatively efficient to store. We use C != OldC to know when
// a new SCC is generated and the original SCC may be generated via merge
// in later iterations.
// It is also possible that even if no new SCC is generated
// (i.e., C == OldC), the original SCC could be split and then merged
// into the same one as itself. and the original SCC will be added into
// UR.CWorklist again, we want to catch such cases too.
// FIXME: This seems like a very heavyweight way of retaining the inline
// history, we should look for a more efficient way of tracking it.
if ((C != OldC || UR.CWorklist.count(OldC)) &&
llvm::any_of(InlinedCallees, [&](Function *Callee) {
return CG.lookupSCC(*CG.lookup(*Callee)) == OldC;
})) {
LLVM_DEBUG(dbgs() << "Inlined an internal call edge and split an SCC, "
"retaining this to avoid infinite inlining.\n");
UR.InlinedInternalEdges.insert({&N, OldC});
// Now that we've finished inlining all of the calls across this SCC, delete
// all of the trivially dead functions, updating the call graph and the CGSCC
// pass manager in the process.
// Note that this walks a pointer set which has non-deterministic order but
// that is OK as all we do is delete things and add pointers to unordered
// sets.
for (Function *DeadF : DeadFunctions) {
// Get the necessary information out of the call graph and nuke the
// function there. Also, cclear out any cached analyses.
auto &DeadC = *CG.lookupSCC(*CG.lookup(*DeadF));
FunctionAnalysisManager &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(DeadC, CG)
FAM.clear(*DeadF, DeadF->getName());
AM.clear(DeadC, DeadC.getName());
auto &DeadRC = DeadC.getOuterRefSCC();
// Mark the relevant parts of the call graph as invalid so we don't visit
// them.
// And delete the actual function from the module.
if (!Changed)
return PreservedAnalyses::all();
// Even if we change the IR, we update the core CGSCC data structures and so
// can preserve the proxy to the function analysis manager.
PreservedAnalyses PA;
return PA;