llvm-project/llvm/lib/Transforms/IPO/Inliner.cpp

549 lines
21 KiB
C++

//===- Inliner.cpp - Code common to all inliners --------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "inline"
#include "llvm/Module.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Analysis/InlineCost.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/IPO/InlinerPass.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include <set>
using namespace llvm;
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");
static cl::opt<int>
InlineLimit("inline-threshold", cl::Hidden, cl::init(225), cl::ZeroOrMore,
cl::desc("Control the amount of inlining to perform (default = 225)"));
static cl::opt<int>
HintThreshold("inlinehint-threshold", cl::Hidden, cl::init(325),
cl::desc("Threshold for inlining functions with inline hint"));
// Threshold to use when optsize is specified (and there is no -inline-limit).
const int OptSizeThreshold = 75;
Inliner::Inliner(void *ID)
: CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {}
Inliner::Inliner(void *ID, int Threshold)
: CallGraphSCCPass(ID), InlineThreshold(Threshold) {}
/// getAnalysisUsage - 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 Inliner::getAnalysisUsage(AnalysisUsage &Info) const {
CallGraphSCCPass::getAnalysisUsage(Info);
}
typedef DenseMap<const ArrayType*, std::vector<AllocaInst*> >
InlinedArrayAllocasTy;
/// InlineCallIfPossible - 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 bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI,
InlinedArrayAllocasTy &InlinedArrayAllocas) {
Function *Callee = CS.getCalledFunction();
Function *Caller = CS.getCaller();
// Try to inline the function. Get the list of static allocas that were
// inlined.
if (!InlineFunction(CS, IFI))
return false;
// If the inlined function had a higher stack protection level than the
// calling function, then bump up the caller's stack protection level.
if (Callee->hasFnAttr(Attribute::StackProtectReq))
Caller->addFnAttr(Attribute::StackProtectReq);
else if (Callee->hasFnAttr(Attribute::StackProtect) &&
!Caller->hasFnAttr(Attribute::StackProtectReq))
Caller->addFnAttr(Attribute::StackProtect);
// 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.
//
SmallPtrSet<AllocaInst*, 16> UsedAllocas;
// 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).
const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType());
if (ATy == 0 || 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 (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) {
AllocaInst *AvailableAlloca = AllocasForType[i];
// 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))
continue;
// Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare
// success!
DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI);
AI->replaceAllUsesWith(AvailableAlloca);
AI->eraseFromParent();
MergedAwayAlloca = true;
++NumMergedAllocas;
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);
}
return true;
}
unsigned Inliner::getInlineThreshold(CallSite CS) const {
int thres = InlineThreshold;
// Listen to optsize when -inline-limit is not given.
Function *Caller = CS.getCaller();
if (Caller && !Caller->isDeclaration() &&
Caller->hasFnAttr(Attribute::OptimizeForSize) &&
InlineLimit.getNumOccurrences() == 0)
thres = OptSizeThreshold;
// Listen to inlinehint when it would increase the threshold.
Function *Callee = CS.getCalledFunction();
if (HintThreshold > thres && Callee && !Callee->isDeclaration() &&
Callee->hasFnAttr(Attribute::InlineHint))
thres = HintThreshold;
return thres;
}
/// shouldInline - Return true if the inliner should attempt to inline
/// at the given CallSite.
bool Inliner::shouldInline(CallSite CS) {
InlineCost IC = getInlineCost(CS);
if (IC.isAlways()) {
DEBUG(dbgs() << " Inlining: cost=always"
<< ", Call: " << *CS.getInstruction() << "\n");
return true;
}
if (IC.isNever()) {
DEBUG(dbgs() << " NOT Inlining: cost=never"
<< ", Call: " << *CS.getInstruction() << "\n");
return false;
}
int Cost = IC.getValue();
Function *Caller = CS.getCaller();
int CurrentThreshold = getInlineThreshold(CS);
float FudgeFactor = getInlineFudgeFactor(CS);
int AdjThreshold = (int)(CurrentThreshold * FudgeFactor);
if (Cost >= AdjThreshold) {
DEBUG(dbgs() << " NOT Inlining: cost=" << Cost
<< ", thres=" << AdjThreshold
<< ", Call: " << *CS.getInstruction() << "\n");
return false;
}
// Try to detect the case where the current inlining candidate caller
// (call it B) is a static 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.
if (Caller->hasLocalLinkage()) {
int TotalSecondaryCost = 0;
bool outerCallsFound = false;
bool allOuterCallsWillBeInlined = true;
bool someOuterCallWouldNotBeInlined = false;
for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end();
I != E; ++I) {
CallSite CS2(*I);
// If this isn't a call to Caller (it could be some other sort
// of reference) skip it.
if (!CS2 || CS2.getCalledFunction() != Caller)
continue;
InlineCost IC2 = getInlineCost(CS2);
if (IC2.isNever())
allOuterCallsWillBeInlined = false;
if (IC2.isAlways() || IC2.isNever())
continue;
outerCallsFound = true;
int Cost2 = IC2.getValue();
int CurrentThreshold2 = getInlineThreshold(CS2);
float FudgeFactor2 = getInlineFudgeFactor(CS2);
if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2))
allOuterCallsWillBeInlined = false;
// See if we have this case. We subtract off the penalty
// for the call instruction, which we would be deleting.
if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) &&
Cost2 + Cost - (InlineConstants::CallPenalty + 1) >=
(int)(CurrentThreshold2 * FudgeFactor2)) {
someOuterCallWouldNotBeInlined = true;
TotalSecondaryCost += Cost2;
}
}
// 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 (allOuterCallsWillBeInlined && Caller->use_begin() != Caller->use_end())
TotalSecondaryCost += InlineConstants::LastCallToStaticBonus;
if (outerCallsFound && someOuterCallWouldNotBeInlined &&
TotalSecondaryCost < Cost) {
DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() <<
" Cost = " << Cost <<
", outer Cost = " << TotalSecondaryCost << '\n');
return false;
}
}
DEBUG(dbgs() << " Inlining: cost=" << Cost
<< ", thres=" << AdjThreshold
<< ", Call: " << *CS.getInstruction() << '\n');
return true;
}
/// InlineHistoryIncludes - 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 Inliner::runOnSCC(CallGraphSCC &SCC) {
CallGraph &CG = getAnalysis<CallGraph>();
const TargetData *TD = getAnalysisIfAvailable<TargetData>();
SmallPtrSet<Function*, 8> SCCFunctions;
DEBUG(dbgs() << "Inliner visiting SCC:");
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (F) SCCFunctions.insert(F);
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 (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
Function *F = (*I)->getFunction();
if (!F) continue;
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
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))
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 (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration())
continue;
CallSites.push_back(std::make_pair(CS, -1));
}
}
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, TD);
// 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.
for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
CallSite CS = CallSites[CSi].first;
Function *Caller = CS.getCaller();
Function *Callee = CS.getCalledFunction();
// 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 (isInstructionTriviallyDead(CS.getInstruction())) {
DEBUG(dbgs() << " -> Deleting dead call: "
<< *CS.getInstruction() << "\n");
// Update the call graph by deleting the edge from Callee to Caller.
CG[Caller]->removeCallEdgeFor(CS);
CS.getInstruction()->eraseFromParent();
++NumCallsDeleted;
// Update the cached cost info with the missing call
growCachedCostInfo(Caller, NULL);
} else {
// We can only inline direct calls to non-declarations.
if (Callee == 0 || Callee->isDeclaration()) continue;
// 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 inlinling the same function,
// which would provide the same callsites, which would cause us to
// infinitely inline.
int InlineHistoryID = CallSites[CSi].second;
if (InlineHistoryID != -1 &&
InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory))
continue;
// If the policy determines that we should inline this function,
// try to do so.
if (!shouldInline(CS))
continue;
// Attempt to inline the function.
if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas))
continue;
++NumInlined;
// 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 (unsigned i = 0, e = InlineInfo.InlinedCalls.size();
i != e; ++i) {
Value *Ptr = InlineInfo.InlinedCalls[i];
CallSites.push_back(std::make_pair(CallSite(Ptr), NewHistoryID));
}
}
// Update the cached cost info with the inlined call.
growCachedCostInfo(Caller, Callee);
}
// 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) {
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();
resetCachedCostInfo(Callee);
// 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;
}
// doFinalization - Remove now-dead linkonce functions at the end of
// processing to avoid breaking the SCC traversal.
bool Inliner::doFinalization(CallGraph &CG) {
return removeDeadFunctions(CG);
}
/// removeDeadFunctions - Remove dead functions that are not included in
/// DNR (Do Not Remove) list.
bool Inliner::removeDeadFunctions(CallGraph &CG,
SmallPtrSet<const Function *, 16> *DNR) {
SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove;
// 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 (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
CallGraphNode *CGN = I->second;
if (CGN->getFunction() == 0)
continue;
Function *F = CGN->getFunction();
// If the only remaining users of the function are dead constants, remove
// them.
F->removeDeadConstantUsers();
if (DNR && DNR->count(F))
continue;
if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() &&
!F->hasAvailableExternallyLinkage())
continue;
if (!F->use_empty())
continue;
// 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.insert(CGN);
}
// 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 set
// here to do this, it doesn't matter which order the functions are deleted
// in.
bool Changed = false;
for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(),
E = FunctionsToRemove.end(); I != E; ++I) {
resetCachedCostInfo((*I)->getFunction());
delete CG.removeFunctionFromModule(*I);
++NumDeleted;
Changed = true;
}
return Changed;
}