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llvm-mirror/lib/Transforms/IPO/Inliner.cpp
Arthur Eubanks f3b675c071 [NewPM][Inliner] Check if deleted function is in current SCC 
In weird cases, the inliner will inline internal recursive functions,
sometimes causing them to have no more uses, in which case the
inliner will mark the function to be deleted. The function is
actually deleted after the call to
updateCGAndAnalysisManagerForCGSCCPass(). In
updateCGAndAnalysisManagerForCGSCCPass(), UR.UpdatedC may be set to
the SCC containing the function to be deleted. Then the inliner calls
CG.removeDeadFunction() which can cause that SCC to be deleted, even
though it's still stored in UR.UpdatedC.

We could potentially check in the wrappers/pass managers if UR.UpdatedC
is in UR.InvalidatedSCCs before doing anything with it, but it's safer
to do this as close to possible to the call to CG.removeDeadFunction()
to avoid issues with allocating a new SCC in the same address as
the deleted one.

It's hard to find a small test case since we need to have recursive
internal functions be reachable from non-internal functions, yet they
need to become non-recursive and not referenced by other functions when
inlined.

Similar to https://reviews.llvm.org/D106306.

Fixes PR50788.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D106405
2021-07-21 08:47:45 -07:00

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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 https://llvm.org/LICENSE.txt 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/ScopeExit.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/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/GlobalsModRef.h"
#include "llvm/Analysis/InlineAdvisor.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/Analysis/Utils/ImportedFunctionsInliningStatistics.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.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/CallPromotionUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.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");
/// 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>
DisableInlinedAllocaMerging("disable-inlined-alloca-merging",
cl::init(false), cl::Hidden);
extern cl::opt<InlinerFunctionImportStatsOpts> InlinerFunctionImportStats;
static cl::opt<std::string> CGSCCInlineReplayFile(
"cgscc-inline-replay", cl::init(""), cl::value_desc("filename"),
cl::desc(
"Optimization remarks file containing inline remarks to be replayed "
"by inlining from cgscc inline remarks."),
cl::Hidden);
static cl::opt<bool> InlineEnablePriorityOrder(
"inline-enable-priority-order", cl::Hidden, cl::init(false),
cl::desc("Enable the priority inline order for the inliner"));
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 {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<ProfileSummaryInfoWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
getAAResultsAnalysisUsage(AU);
CallGraphSCCPass::getAnalysisUsage(AU);
}
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 the call site 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.
return;
// 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())
continue;
// 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) {
Align Align1 = AI->getAlign();
Align Align2 = AvailableAlloca->getAlign();
// The available alloca has to be in the right function, not in some other
// function in this SCC.
if (AvailableAlloca->getParent() != AI->getParent())
continue;
// If the inlined function already uses this alloca then we can't reuse
// it.
if (!UsedAllocas.insert(AvailableAlloca).second)
continue;
// 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))
DDI->moveBefore(AvailableAlloca->getNextNode());
AI->replaceAllUsesWith(AvailableAlloca);
if (Align1 > Align2)
AvailableAlloca->setAlignment(AI->getAlign());
AI->eraseFromParent();
MergedAwayAlloca = true;
++NumMergedAllocas;
IFI.StaticAllocas[AllocaNo] = nullptr;
break;
}
// If we already nuked the alloca, we're done with it.
if (MergedAwayAlloca)
continue;
// 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.
AllocasForType.push_back(AI);
UsedAllocas.insert(AI);
}
}
/// 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(
CallBase &CB, InlineFunctionInfo &IFI,
InlinedArrayAllocasTy &InlinedArrayAllocas, int InlineHistory,
bool InsertLifetime, function_ref<AAResults &(Function &)> &AARGetter,
ImportedFunctionsInliningStatistics &ImportedFunctionsStats) {
Function *Callee = CB.getCalledFunction();
Function *Caller = CB.getCaller();
AAResults &AAR = AARGetter(*Callee);
// Try to inline the function. Get the list of static allocas that were
// inlined.
InlineResult IR = InlineFunction(CB, IFI, &AAR, InsertLifetime);
if (!IR.isSuccess())
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 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)
ImportedFunctionsStats.setModuleInfo(CG.getModule());
return false; // No changes to CallGraph.
}
bool LegacyInlinerBase::runOnSCC(CallGraphSCC &SCC) {
if (skipSCC(SCC))
return false;
return inlineCalls(SCC);
}
static bool
inlineCallsImpl(CallGraphSCC &SCC, CallGraph &CG,
std::function<AssumptionCache &(Function &)> GetAssumptionCache,
ProfileSummaryInfo *PSI,
std::function<const TargetLibraryInfo &(Function &)> GetTLI,
bool InsertLifetime,
function_ref<InlineCost(CallBase &CB)> 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)
SCCFunctions.insert(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<CallBase *, 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())
continue;
OptimizationRemarkEmitter ORE(F);
for (BasicBlock &BB : *F)
for (Instruction &I : BB) {
auto *CB = dyn_cast<CallBase>(&I);
// If this isn't a call, or it is a call to an intrinsic, it can
// never be inlined.
if (!CB || isa<IntrinsicInst>(I))
continue;
// 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 = CB->getCalledFunction())
if (Callee->isDeclaration()) {
using namespace ore;
setInlineRemark(*CB, "unavailable definition");
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
<< NV("Callee", Callee) << " will not be inlined into "
<< NV("Caller", CB->getCaller())
<< " because its definition is unavailable"
<< setIsVerbose();
});
continue;
}
CallSites.push_back(std::make_pair(CB, -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) {
auto &P = CallSites[CSi];
CallBase &CB = *P.first;
const int InlineHistoryID = P.second;
Function *Caller = CB.getCaller();
Function *Callee = CB.getCalledFunction();
// We can only inline direct calls to non-declarations.
if (!Callee || Callee->isDeclaration())
continue;
bool IsTriviallyDead = isInstructionTriviallyDead(&CB, &GetTLI(*Caller));
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.
if (InlineHistoryID != -1 &&
inlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory)) {
setInlineRemark(CB, "recursive");
continue;
}
}
// 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);
auto OIC = shouldInline(CB, GetInlineCost, ORE);
// If the policy determines that we should inline this function,
// delete the call instead.
if (!OIC)
continue;
// 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: " << CB << "\n");
// Update the call graph by deleting the edge from Callee to Caller.
setInlineRemark(CB, "trivially dead");
CG[Caller]->removeCallEdgeFor(CB);
CB.eraseFromParent();
++NumCallsDeleted;
} else {
// Get DebugLoc to report. CB will be invalid after Inliner.
DebugLoc DLoc = CB.getDebugLoc();
BasicBlock *Block = CB.getParent();
// Attempt to inline the function.
using namespace ore;
InlineResult IR = inlineCallIfPossible(
CB, InlineInfo, InlinedArrayAllocas, InlineHistoryID,
InsertLifetime, AARGetter, ImportedFunctionsStats);
if (!IR.isSuccess()) {
setInlineRemark(CB, std::string(IR.getFailureReason()) + "; " +
inlineCostStr(*OIC));
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc,
Block)
<< NV("Callee", Callee) << " will not be inlined into "
<< NV("Caller", Caller) << ": "
<< NV("Reason", IR.getFailureReason());
});
continue;
}
++NumInlined;
emitInlinedInto(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));
#ifndef NDEBUG
// Make sure no dupplicates in the inline candidates. This could
// happen when a callsite is simpilfied to reusing the return value
// of another callsite during function cloning, thus the other
// callsite will be reconsidered here.
DenseSet<CallBase *> DbgCallSites;
for (auto &II : CallSites)
DbgCallSites.insert(II.first);
#endif
for (Value *Ptr : InlineInfo.InlinedCalls) {
#ifndef NDEBUG
assert(DbgCallSites.count(dyn_cast<CallBase>(Ptr)) == 0);
#endif
CallSites.push_back(
std::make_pair(dyn_cast<CallBase>(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.
CalleeNode->removeAllCalledFunctions();
// Removing the node for callee from the call graph and delete it.
delete CG.removeFunctionFromModule(CalleeNode);
++NumDeleted;
}
// 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();
CallSites.pop_back();
} else {
CallSites.erase(CallSites.begin() + CSi);
}
--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();
GetTLI = [&](Function &F) -> const TargetLibraryInfo & {
return getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
};
auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
return ACT->getAssumptionCache(F);
};
return inlineCallsImpl(
SCC, CG, GetAssumptionCache, PSI, GetTLI, InsertLifetime,
[&](CallBase &CB) { return getInlineCost(CB); }, LegacyAARGetter(*this),
ImportedFunctionsStats);
}
/// 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 ==
InlinerFunctionImportStatsOpts::Verbose);
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.
CGN->removeAllCalledFunctions();
// 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.
CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
// Removing the node for callee from the call graph and delete it.
FunctionsToRemove.push_back(CGN);
};
// 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())
continue;
// 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))
continue;
// If the only remaining users of the function are dead constants, remove
// them.
F->removeDeadConstantUsers();
if (!F->isDefTriviallyDead())
continue;
// 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()) {
DeadFunctionsInComdats.push_back(F);
continue;
}
}
RemoveCGN(CGN);
}
if (!DeadFunctionsInComdats.empty()) {
// Filter out the functions whose comdats remain alive.
filterDeadComdatFunctions(CG.getModule(), DeadFunctionsInComdats);
// Remove the rest.
for (Function *F : DeadFunctionsInComdats)
RemoveCGN(CG[F]);
}
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());
FunctionsToRemove.erase(
std::unique(FunctionsToRemove.begin(), FunctionsToRemove.end()),
FunctionsToRemove.end());
for (CallGraphNode *CGN : FunctionsToRemove) {
delete CG.removeFunctionFromModule(CGN);
++NumDeleted;
}
return true;
}
InlineAdvisor &
InlinerPass::getAdvisor(const ModuleAnalysisManagerCGSCCProxy::Result &MAM,
FunctionAnalysisManager &FAM, Module &M) {
if (OwnedAdvisor)
return *OwnedAdvisor;
auto *IAA = MAM.getCachedResult<InlineAdvisorAnalysis>(M);
if (!IAA) {
// It should still be possible to run the inliner as a stand-alone SCC pass,
// for test scenarios. In that case, we default to the
// DefaultInlineAdvisor, which doesn't need to keep state between SCC pass
// runs. It also uses just the default InlineParams.
// In this case, we need to use the provided FAM, which is valid for the
// duration of the inliner pass, and thus the lifetime of the owned advisor.
// The one we would get from the MAM can be invalidated as a result of the
// inliner's activity.
OwnedAdvisor =
std::make_unique<DefaultInlineAdvisor>(M, FAM, getInlineParams());
if (!CGSCCInlineReplayFile.empty())
OwnedAdvisor = std::make_unique<ReplayInlineAdvisor>(
M, FAM, M.getContext(), std::move(OwnedAdvisor),
CGSCCInlineReplayFile,
/*EmitRemarks=*/true);
return *OwnedAdvisor;
}
assert(IAA->getAdvisor() &&
"Expected a present InlineAdvisorAnalysis also have an "
"InlineAdvisor initialized");
return *IAA->getAdvisor();
}
template <typename T> class InlineOrder {
public:
using reference = T &;
using const_reference = const T &;
virtual ~InlineOrder() {}
virtual size_t size() = 0;
virtual void push(const T &Elt) = 0;
virtual T pop() = 0;
virtual const_reference front() = 0;
virtual void erase_if(function_ref<bool(T)> Pred) = 0;
bool empty() { return !size(); }
};
template <typename T, typename Container = SmallVector<T, 16>>
class DefaultInlineOrder : public InlineOrder<T> {
using reference = T &;
using const_reference = const T &;
public:
size_t size() override { return Calls.size() - FirstIndex; }
void push(const T &Elt) override { Calls.push_back(Elt); }
T pop() override {
assert(size() > 0);
return Calls[FirstIndex++];
}
const_reference front() override {
assert(size() > 0);
return Calls[FirstIndex];
}
void erase_if(function_ref<bool(T)> Pred) override {
Calls.erase(std::remove_if(Calls.begin() + FirstIndex, Calls.end(), Pred),
Calls.end());
}
private:
Container Calls;
size_t FirstIndex = 0;
};
class Priority {
public:
Priority(int Size) : Size(Size) {}
static bool isMoreDesirable(const Priority &S1, const Priority &S2) {
return S1.Size < S2.Size;
}
static Priority evaluate(CallBase *CB) {
Function *Callee = CB->getCalledFunction();
return Priority(Callee->getInstructionCount());
}
int Size;
};
template <typename PriorityT>
class PriorityInlineOrder : public InlineOrder<std::pair<CallBase *, int>> {
using T = std::pair<CallBase *, int>;
using HeapT = std::pair<CallBase *, PriorityT>;
using reference = T &;
using const_reference = const T &;
static bool cmp(const HeapT &P1, const HeapT &P2) {
return PriorityT::isMoreDesirable(P2.second, P1.second);
}
// A call site could become less desirable for inlining because of the size
// growth from prior inlining into the callee. This method is used to lazily
// update the desirability of a call site if it's decreasing. It is only
// called on pop() or front(), not every time the desirability changes. When
// the desirability of the front call site decreases, an updated one would be
// pushed right back into the heap. For simplicity, those cases where
// the desirability of a call site increases are ignored here.
void adjust() {
bool Changed = false;
do {
CallBase *CB = Heap.front().first;
const PriorityT PreviousGoodness = Heap.front().second;
const PriorityT CurrentGoodness = PriorityT::evaluate(CB);
Changed = PriorityT::isMoreDesirable(PreviousGoodness, CurrentGoodness);
if (Changed) {
std::pop_heap(Heap.begin(), Heap.end(), cmp);
Heap.pop_back();
Heap.push_back({CB, CurrentGoodness});
std::push_heap(Heap.begin(), Heap.end(), cmp);
}
} while (Changed);
}
public:
size_t size() override { return Heap.size(); }
void push(const T &Elt) override {
CallBase *CB = Elt.first;
const int InlineHistoryID = Elt.second;
const PriorityT Goodness = PriorityT::evaluate(CB);
Heap.push_back({CB, Goodness});
std::push_heap(Heap.begin(), Heap.end(), cmp);
InlineHistoryMap[CB] = InlineHistoryID;
}
T pop() override {
assert(size() > 0);
adjust();
CallBase *CB = Heap.front().first;
T Result = std::make_pair(CB, InlineHistoryMap[CB]);
InlineHistoryMap.erase(CB);
std::pop_heap(Heap.begin(), Heap.end(), cmp);
Heap.pop_back();
return Result;
}
const_reference front() override {
assert(size() > 0);
adjust();
CallBase *CB = Heap.front().first;
return *InlineHistoryMap.find(CB);
}
void erase_if(function_ref<bool(T)> Pred) override {
auto PredWrapper = [=](HeapT P) -> bool {
return Pred(std::make_pair(P.first, 0));
};
Heap.erase(std::remove_if(Heap.begin(), Heap.end(), PredWrapper),
Heap.end());
std::make_heap(Heap.begin(), Heap.end(), cmp);
}
private:
SmallVector<HeapT, 16> Heap;
DenseMap<CallBase *, int> InlineHistoryMap;
};
PreservedAnalyses InlinerPass::run(LazyCallGraph::SCC &InitialC,
CGSCCAnalysisManager &AM, LazyCallGraph &CG,
CGSCCUpdateResult &UR) {
const auto &MAMProxy =
AM.getResult<ModuleAnalysisManagerCGSCCProxy>(InitialC, CG);
bool Changed = false;
assert(InitialC.size() > 0 && "Cannot handle an empty SCC!");
Module &M = *InitialC.begin()->getFunction().getParent();
ProfileSummaryInfo *PSI = MAMProxy.getCachedResult<ProfileSummaryAnalysis>(M);
FunctionAnalysisManager &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(InitialC, CG)
.getManager();
InlineAdvisor &Advisor = getAdvisor(MAMProxy, FAM, M);
Advisor.onPassEntry();
auto AdvisorOnExit = make_scope_exit([&] { Advisor.onPassExit(); });
// 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. The PriorityInlineOrder is optional here, in which the smaller
// callee would have a higher priority to inline.
//
// 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 amount 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.
std::unique_ptr<InlineOrder<std::pair<CallBase *, int>>> Calls;
if (InlineEnablePriorityOrder)
Calls = std::make_unique<PriorityInlineOrder<Priority>>();
else
Calls = std::make_unique<DefaultInlineOrder<std::pair<CallBase *, int>>>();
assert(Calls != nullptr && "Expected an initialized InlineOrder");
// Populate the initial list of calls in this SCC.
for (auto &N : InitialC) {
auto &ORE =
FAM.getResult<OptimizationRemarkEmitterAnalysis>(N.getFunction());
// 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 *CB = dyn_cast<CallBase>(&I))
if (Function *Callee = CB->getCalledFunction()) {
if (!Callee->isDeclaration())
Calls->push({CB, -1});
else if (!isa<IntrinsicInst>(I)) {
using namespace ore;
setInlineRemark(*CB, "unavailable definition");
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
<< NV("Callee", Callee) << " will not be inlined into "
<< NV("Caller", CB->getCaller())
<< " because its definition is unavailable"
<< setIsVerbose();
});
}
}
}
if (Calls->empty())
return PreservedAnalyses::all();
// Capture updatable variable for the current SCC.
auto *C = &InitialC;
// 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.
while (!Calls->empty()) {
// 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->front().first->getCaller();
LazyCallGraph::Node &N = *CG.lookup(F);
if (CG.lookupSCC(N) != C) {
Calls->pop();
continue;
}
LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n"
<< " Function size: " << F.getInstructionCount()
<< "\n");
auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
return FAM.getResult<AssumptionAnalysis>(F);
};
// Now process as many calls as we have within this caller in the sequence.
// 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;
while (!Calls->empty() && Calls->front().first->getCaller() == &F) {
auto P = Calls->pop();
CallBase *CB = P.first;
const int InlineHistoryID = P.second;
Function &Callee = *CB->getCalledFunction();
if (InlineHistoryID != -1 &&
inlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory)) {
setInlineRemark(*CB, "recursive");
continue;
}
// 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(*CB, "recursive SCC split");
continue;
}
auto Advice = Advisor.getAdvice(*CB, OnlyMandatory);
// Check whether we want to inline this callsite.
if (!Advice->isInliningRecommended()) {
Advice->recordUnattemptedInlining();
continue;
}
// Setup the data structure used to plumb customization into the
// `InlineFunction` routine.
InlineFunctionInfo IFI(
/*cg=*/nullptr, GetAssumptionCache, PSI,
&FAM.getResult<BlockFrequencyAnalysis>(*(CB->getCaller())),
&FAM.getResult<BlockFrequencyAnalysis>(Callee));
InlineResult IR =
InlineFunction(*CB, IFI, &FAM.getResult<AAManager>(*CB->getCaller()));
if (!IR.isSuccess()) {
Advice->recordUnsuccessfulInlining(IR);
continue;
}
DidInline = true;
InlinedCallees.insert(&Callee);
++NumInlined;
LLVM_DEBUG(dbgs() << " Size after inlining: "
<< F.getInstructionCount() << "\n");
// Add any new callsites to defined functions to the worklist.
if (!IFI.InlinedCallSites.empty()) {
int NewHistoryID = InlineHistory.size();
InlineHistory.push_back({&Callee, InlineHistoryID});
for (CallBase *ICB : reverse(IFI.InlinedCallSites)) {
Function *NewCallee = ICB->getCalledFunction();
assert(!(NewCallee && NewCallee->isIntrinsic()) &&
"Intrinsic calls should not be tracked.");
if (!NewCallee) {
// Try to promote an indirect (virtual) call without waiting for
// the post-inline cleanup and the next DevirtSCCRepeatedPass
// iteration because the next iteration may not happen and we may
// miss inlining it.
if (tryPromoteCall(*ICB))
NewCallee = ICB->getCalledFunction();
}
if (NewCallee)
if (!NewCallee->isDeclaration())
Calls->push({ICB, NewHistoryID});
}
}
// 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.
bool CalleeWasDeleted = false;
if (Callee.hasLocalLinkage()) {
// To check this we also need to nuke any dead constant uses (perhaps
// made dead by this operation on other functions).
Callee.removeDeadConstantUsers();
if (Callee.use_empty() && !CG.isLibFunction(Callee)) {
Calls->erase_if([&](const std::pair<CallBase *, 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.
Callee.dropAllReferences();
assert(!is_contained(DeadFunctions, &Callee) &&
"Cannot put cause a function to become dead twice!");
DeadFunctions.push_back(&Callee);
CalleeWasDeleted = true;
}
}
if (CalleeWasDeleted)
Advice->recordInliningWithCalleeDeleted();
else
Advice->recordInlining();
}
if (!DidInline)
continue;
Changed = true;
// 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.
// Inside the update, we also update the FunctionAnalysisManager in the
// proxy for this particular SCC. We do this 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.
LazyCallGraph::SCC *OldC = C;
C = &updateCGAndAnalysisManagerForCGSCCPass(CG, *C, N, AM, UR, FAM);
LLVM_DEBUG(dbgs() << "Updated inlining SCC: " << *C << "\n");
// 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});
}
InlinedCallees.clear();
}
// 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, clear out any cached analyses.
auto &DeadC = *CG.lookupSCC(*CG.lookup(*DeadF));
FAM.clear(*DeadF, DeadF->getName());
AM.clear(DeadC, DeadC.getName());
auto &DeadRC = DeadC.getOuterRefSCC();
CG.removeDeadFunction(*DeadF);
// Mark the relevant parts of the call graph as invalid so we don't visit
// them.
UR.InvalidatedSCCs.insert(&DeadC);
UR.InvalidatedRefSCCs.insert(&DeadRC);
// If the updated SCC was the one containing the deleted function, clear it.
if (&DeadC == UR.UpdatedC)
UR.UpdatedC = nullptr;
// And delete the actual function from the module.
// The Advisor may use Function pointers to efficiently index various
// internal maps, e.g. for memoization. Function cleanup passes like
// argument promotion create new functions. It is possible for a new
// function to be allocated at the address of a deleted function. We could
// index using names, but that's inefficient. Alternatively, we let the
// Advisor free the functions when it sees fit.
DeadF->getBasicBlockList().clear();
M.getFunctionList().remove(DeadF);
++NumDeleted;
}
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;
PA.preserve<FunctionAnalysisManagerCGSCCProxy>();
return PA;
}
ModuleInlinerWrapperPass::ModuleInlinerWrapperPass(InlineParams Params,
bool MandatoryFirst,
InliningAdvisorMode Mode,
unsigned MaxDevirtIterations)
: Params(Params), Mode(Mode), MaxDevirtIterations(MaxDevirtIterations),
PM(), MPM() {
// Run the inliner first. The theory is that we are walking bottom-up and so
// the callees have already been fully optimized, and we want to inline them
// into the callers so that our optimizations can reflect that.
// For PreLinkThinLTO pass, we disable hot-caller heuristic for sample PGO
// because it makes profile annotation in the backend inaccurate.
if (MandatoryFirst)
PM.addPass(InlinerPass(/*OnlyMandatory*/ true));
PM.addPass(InlinerPass());
}
PreservedAnalyses ModuleInlinerWrapperPass::run(Module &M,
ModuleAnalysisManager &MAM) {
auto &IAA = MAM.getResult<InlineAdvisorAnalysis>(M);
if (!IAA.tryCreate(Params, Mode, CGSCCInlineReplayFile)) {
M.getContext().emitError(
"Could not setup Inlining Advisor for the requested "
"mode and/or options");
return PreservedAnalyses::all();
}
// We wrap the CGSCC pipeline in a devirtualization repeater. This will try
// to detect when we devirtualize indirect calls and iterate the SCC passes
// in that case to try and catch knock-on inlining or function attrs
// opportunities. Then we add it to the module pipeline by walking the SCCs
// in postorder (or bottom-up).
// If MaxDevirtIterations is 0, we just don't use the devirtualization
// wrapper.
if (MaxDevirtIterations == 0)
MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(std::move(PM)));
else
MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(
createDevirtSCCRepeatedPass(std::move(PM), MaxDevirtIterations)));
MPM.run(M, MAM);
IAA.clear();
// The ModulePassManager has already taken care of invalidating analyses.
return PreservedAnalyses::all();
}
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