1 //===- Inliner.cpp - Code common to all inliners --------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the mechanics required to implement inlining without
11 // missing any calls and updating the call graph. The decisions of which calls
12 // are profitable to inline are implemented elsewhere.
14 //===----------------------------------------------------------------------===//
16 #define DEBUG_TYPE "inline"
17 #include "llvm/Module.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/IntrinsicInst.h"
20 #include "llvm/Analysis/CallGraph.h"
21 #include "llvm/Analysis/InlineCost.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/Transforms/IPO/InlinerPass.h"
25 #include "llvm/Transforms/Utils/Cloning.h"
26 #include "llvm/Transforms/Utils/Local.h"
27 #include "llvm/Support/CallSite.h"
28 #include "llvm/Support/CommandLine.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/ADT/SmallPtrSet.h"
32 #include "llvm/ADT/Statistic.h"
35 STATISTIC(NumInlined, "Number of functions inlined");
36 STATISTIC(NumCallsDeleted, "Number of call sites deleted, not inlined");
37 STATISTIC(NumDeleted, "Number of functions deleted because all callers found");
38 STATISTIC(NumMergedAllocas, "Number of allocas merged together");
41 InlineLimit("inline-threshold", cl::Hidden, cl::init(225), cl::ZeroOrMore,
42 cl::desc("Control the amount of inlining to perform (default = 225)"));
45 HintThreshold("inlinehint-threshold", cl::Hidden, cl::init(325),
46 cl::desc("Threshold for inlining functions with inline hint"));
48 // Threshold to use when optsize is specified (and there is no -inline-limit).
49 const int OptSizeThreshold = 75;
51 Inliner::Inliner(char &ID)
52 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit), InsertLifetime(true) {}
54 Inliner::Inliner(char &ID, int Threshold, bool InsertLifetime)
55 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit.getNumOccurrences() > 0 ?
56 InlineLimit : Threshold),
57 InsertLifetime(InsertLifetime) {}
59 /// getAnalysisUsage - For this class, we declare that we require and preserve
60 /// the call graph. If the derived class implements this method, it should
61 /// always explicitly call the implementation here.
62 void Inliner::getAnalysisUsage(AnalysisUsage &Info) const {
63 CallGraphSCCPass::getAnalysisUsage(Info);
67 typedef DenseMap<ArrayType*, std::vector<AllocaInst*> >
68 InlinedArrayAllocasTy;
70 /// InlineCallIfPossible - If it is possible to inline the specified call site,
71 /// do so and update the CallGraph for this operation.
73 /// This function also does some basic book-keeping to update the IR. The
74 /// InlinedArrayAllocas map keeps track of any allocas that are already
75 /// available from other functions inlined into the caller. If we are able to
76 /// inline this call site we attempt to reuse already available allocas or add
77 /// any new allocas to the set if not possible.
78 static bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI,
79 InlinedArrayAllocasTy &InlinedArrayAllocas,
80 int InlineHistory, bool InsertLifetime) {
81 Function *Callee = CS.getCalledFunction();
82 Function *Caller = CS.getCaller();
84 // Try to inline the function. Get the list of static allocas that were
86 if (!InlineFunction(CS, IFI, InsertLifetime))
89 // If the inlined function had a higher stack protection level than the
90 // calling function, then bump up the caller's stack protection level.
91 if (Callee->hasFnAttr(Attribute::StackProtectReq))
92 Caller->addFnAttr(Attribute::StackProtectReq);
93 else if (Callee->hasFnAttr(Attribute::StackProtect) &&
94 !Caller->hasFnAttr(Attribute::StackProtectReq))
95 Caller->addFnAttr(Attribute::StackProtect);
97 // Look at all of the allocas that we inlined through this call site. If we
98 // have already inlined other allocas through other calls into this function,
99 // then we know that they have disjoint lifetimes and that we can merge them.
101 // There are many heuristics possible for merging these allocas, and the
102 // different options have different tradeoffs. One thing that we *really*
103 // don't want to hurt is SRoA: once inlining happens, often allocas are no
104 // longer address taken and so they can be promoted.
106 // Our "solution" for that is to only merge allocas whose outermost type is an
107 // array type. These are usually not promoted because someone is using a
108 // variable index into them. These are also often the most important ones to
111 // A better solution would be to have real memory lifetime markers in the IR
112 // and not have the inliner do any merging of allocas at all. This would
113 // allow the backend to do proper stack slot coloring of all allocas that
114 // *actually make it to the backend*, which is really what we want.
116 // Because we don't have this information, we do this simple and useful hack.
118 SmallPtrSet<AllocaInst*, 16> UsedAllocas;
120 // When processing our SCC, check to see if CS was inlined from some other
121 // call site. For example, if we're processing "A" in this code:
123 // B() { x = alloca ... C() }
124 // C() { y = alloca ... }
125 // Assume that C was not inlined into B initially, and so we're processing A
126 // and decide to inline B into A. Doing this makes an alloca available for
127 // reuse and makes a callsite (C) available for inlining. When we process
128 // the C call site we don't want to do any alloca merging between X and Y
129 // because their scopes are not disjoint. We could make this smarter by
130 // keeping track of the inline history for each alloca in the
131 // InlinedArrayAllocas but this isn't likely to be a significant win.
132 if (InlineHistory != -1) // Only do merging for top-level call sites in SCC.
135 // Loop over all the allocas we have so far and see if they can be merged with
136 // a previously inlined alloca. If not, remember that we had it.
137 for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size();
138 AllocaNo != e; ++AllocaNo) {
139 AllocaInst *AI = IFI.StaticAllocas[AllocaNo];
141 // Don't bother trying to merge array allocations (they will usually be
142 // canonicalized to be an allocation *of* an array), or allocations whose
143 // type is not itself an array (because we're afraid of pessimizing SRoA).
144 ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType());
145 if (ATy == 0 || AI->isArrayAllocation())
148 // Get the list of all available allocas for this array type.
149 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy];
151 // Loop over the allocas in AllocasForType to see if we can reuse one. Note
152 // that we have to be careful not to reuse the same "available" alloca for
153 // multiple different allocas that we just inlined, we use the 'UsedAllocas'
154 // set to keep track of which "available" allocas are being used by this
155 // function. Also, AllocasForType can be empty of course!
156 bool MergedAwayAlloca = false;
157 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) {
158 AllocaInst *AvailableAlloca = AllocasForType[i];
160 // The available alloca has to be in the right function, not in some other
161 // function in this SCC.
162 if (AvailableAlloca->getParent() != AI->getParent())
165 // If the inlined function already uses this alloca then we can't reuse
167 if (!UsedAllocas.insert(AvailableAlloca))
170 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare
172 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI << "\n\t\tINTO: "
173 << *AvailableAlloca << '\n');
175 AI->replaceAllUsesWith(AvailableAlloca);
176 AI->eraseFromParent();
177 MergedAwayAlloca = true;
179 IFI.StaticAllocas[AllocaNo] = 0;
183 // If we already nuked the alloca, we're done with it.
184 if (MergedAwayAlloca)
187 // If we were unable to merge away the alloca either because there are no
188 // allocas of the right type available or because we reused them all
189 // already, remember that this alloca came from an inlined function and mark
190 // it used so we don't reuse it for other allocas from this inline
192 AllocasForType.push_back(AI);
193 UsedAllocas.insert(AI);
199 unsigned Inliner::getInlineThreshold(CallSite CS) const {
200 int thres = InlineThreshold;
202 // Listen to optsize when -inline-limit is not given.
203 Function *Caller = CS.getCaller();
204 if (Caller && !Caller->isDeclaration() &&
205 Caller->hasFnAttr(Attribute::OptimizeForSize) &&
206 InlineLimit.getNumOccurrences() == 0)
207 thres = OptSizeThreshold;
209 // Listen to inlinehint when it would increase the threshold.
210 Function *Callee = CS.getCalledFunction();
211 if (HintThreshold > thres && Callee && !Callee->isDeclaration() &&
212 Callee->hasFnAttr(Attribute::InlineHint))
213 thres = HintThreshold;
218 /// shouldInline - Return true if the inliner should attempt to inline
219 /// at the given CallSite.
220 bool Inliner::shouldInline(CallSite CS) {
221 InlineCost IC = getInlineCost(CS);
224 DEBUG(dbgs() << " Inlining: cost=always"
225 << ", Call: " << *CS.getInstruction() << "\n");
230 DEBUG(dbgs() << " NOT Inlining: cost=never"
231 << ", Call: " << *CS.getInstruction() << "\n");
235 int Cost = IC.getValue();
236 Function *Caller = CS.getCaller();
237 int CurrentThreshold = getInlineThreshold(CS);
238 float FudgeFactor = getInlineFudgeFactor(CS);
239 int AdjThreshold = (int)(CurrentThreshold * FudgeFactor);
240 if (Cost >= AdjThreshold) {
241 DEBUG(dbgs() << " NOT Inlining: cost=" << Cost
242 << ", thres=" << AdjThreshold
243 << ", Call: " << *CS.getInstruction() << "\n");
247 // Try to detect the case where the current inlining candidate caller (call
248 // it B) is a static or linkonce-ODR function and is an inlining candidate
249 // elsewhere, and the current candidate callee (call it C) is large enough
250 // that inlining it into B would make B too big to inline later. In these
251 // circumstances it may be best not to inline C into B, but to inline B into
254 // This only applies to static and linkonce-ODR functions because those are
255 // expected to be available for inlining in the translation units where they
256 // are used. Thus we will always have the opportunity to make local inlining
257 // decisions. Importantly the linkonce-ODR linkage covers inline functions
258 // and templates in C++.
259 if (Caller->hasLocalLinkage() ||
260 Caller->getLinkage() == GlobalValue::LinkOnceODRLinkage) {
261 int TotalSecondaryCost = 0;
262 bool outerCallsFound = false;
263 // This bool tracks what happens if we do NOT inline C into B.
264 bool callerWillBeRemoved = true;
265 // This bool tracks what happens if we DO inline C into B.
266 bool inliningPreventsSomeOuterInline = false;
267 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end();
271 // If this isn't a call to Caller (it could be some other sort
272 // of reference) skip it. Such references will prevent the caller
273 // from being removed.
274 if (!CS2 || CS2.getCalledFunction() != Caller) {
275 callerWillBeRemoved = false;
279 InlineCost IC2 = getInlineCost(CS2);
281 callerWillBeRemoved = false;
282 if (IC2.isAlways() || IC2.isNever())
285 outerCallsFound = true;
286 int Cost2 = IC2.getValue();
287 int CurrentThreshold2 = getInlineThreshold(CS2);
288 float FudgeFactor2 = getInlineFudgeFactor(CS2);
290 if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2))
291 callerWillBeRemoved = false;
293 // See if we have this case. We subtract off the penalty
294 // for the call instruction, which we would be deleting.
295 if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) &&
296 Cost2 + Cost - (InlineConstants::CallPenalty + 1) >=
297 (int)(CurrentThreshold2 * FudgeFactor2)) {
298 inliningPreventsSomeOuterInline = true;
299 TotalSecondaryCost += Cost2;
302 // If all outer calls to Caller would get inlined, the cost for the last
303 // one is set very low by getInlineCost, in anticipation that Caller will
304 // be removed entirely. We did not account for this above unless there
305 // is only one caller of Caller.
306 if (callerWillBeRemoved && Caller->use_begin() != Caller->use_end())
307 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus;
309 if (outerCallsFound && inliningPreventsSomeOuterInline &&
310 TotalSecondaryCost < Cost) {
311 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() <<
312 " Cost = " << Cost <<
313 ", outer Cost = " << TotalSecondaryCost << '\n');
318 DEBUG(dbgs() << " Inlining: cost=" << Cost
319 << ", thres=" << AdjThreshold
320 << ", Call: " << *CS.getInstruction() << '\n');
324 /// InlineHistoryIncludes - Return true if the specified inline history ID
325 /// indicates an inline history that includes the specified function.
326 static bool InlineHistoryIncludes(Function *F, int InlineHistoryID,
327 const SmallVectorImpl<std::pair<Function*, int> > &InlineHistory) {
328 while (InlineHistoryID != -1) {
329 assert(unsigned(InlineHistoryID) < InlineHistory.size() &&
330 "Invalid inline history ID");
331 if (InlineHistory[InlineHistoryID].first == F)
333 InlineHistoryID = InlineHistory[InlineHistoryID].second;
338 /// \brief Simplify arguments going into a particular callsite.
340 /// This is important to do each time we add a callsite due to inlining so that
341 /// constants and other entities which feed into inline cost estimation are
342 /// properly recognized when analyzing the new callsite. Consider:
343 /// void outer(int x) {
345 /// return inner(42 - x);
348 /// void inner(int x) {
352 /// The inliner gives calls to 'outer' with a constant argument a bonus because
353 /// it will delete one side of a branch. But the resulting call to 'inner'
354 /// will, after inlining, also have a constant operand. We need to do just
355 /// enough constant folding to expose this for callsite arguments. The rest
356 /// will be taken care of after the inliner finishes running.
357 static void simplifyCallSiteArguments(const TargetData *TD, CallSite CS) {
358 // FIXME: It would be nice to avoid this smallvector if RAUW doesn't
359 // invalidate operand iterators in any cases.
360 SmallVector<std::pair<Value *, Value*>, 4> SimplifiedArgs;
361 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
363 if (Instruction *Inst = dyn_cast<Instruction>(*I))
364 if (Value *SimpleArg = SimplifyInstruction(Inst, TD))
365 SimplifiedArgs.push_back(std::make_pair(Inst, SimpleArg));
366 for (unsigned Idx = 0, Size = SimplifiedArgs.size(); Idx != Size; ++Idx)
367 SimplifiedArgs[Idx].first->replaceAllUsesWith(SimplifiedArgs[Idx].second);
370 bool Inliner::runOnSCC(CallGraphSCC &SCC) {
371 CallGraph &CG = getAnalysis<CallGraph>();
372 const TargetData *TD = getAnalysisIfAvailable<TargetData>();
374 SmallPtrSet<Function*, 8> SCCFunctions;
375 DEBUG(dbgs() << "Inliner visiting SCC:");
376 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
377 Function *F = (*I)->getFunction();
378 if (F) SCCFunctions.insert(F);
379 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE"));
382 // Scan through and identify all call sites ahead of time so that we only
383 // inline call sites in the original functions, not call sites that result
384 // from inlining other functions.
385 SmallVector<std::pair<CallSite, int>, 16> CallSites;
387 // When inlining a callee produces new call sites, we want to keep track of
388 // the fact that they were inlined from the callee. This allows us to avoid
389 // infinite inlining in some obscure cases. To represent this, we use an
390 // index into the InlineHistory vector.
391 SmallVector<std::pair<Function*, int>, 8> InlineHistory;
393 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
394 Function *F = (*I)->getFunction();
397 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
398 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
399 CallSite CS(cast<Value>(I));
400 // If this isn't a call, or it is a call to an intrinsic, it can
402 if (!CS || isa<IntrinsicInst>(I))
405 // If this is a direct call to an external function, we can never inline
406 // it. If it is an indirect call, inlining may resolve it to be a
407 // direct call, so we keep it.
408 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration())
411 CallSites.push_back(std::make_pair(CS, -1));
415 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n");
417 // If there are no calls in this function, exit early.
418 if (CallSites.empty())
421 // Now that we have all of the call sites, move the ones to functions in the
422 // current SCC to the end of the list.
423 unsigned FirstCallInSCC = CallSites.size();
424 for (unsigned i = 0; i < FirstCallInSCC; ++i)
425 if (Function *F = CallSites[i].first.getCalledFunction())
426 if (SCCFunctions.count(F))
427 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
430 InlinedArrayAllocasTy InlinedArrayAllocas;
431 InlineFunctionInfo InlineInfo(&CG, TD);
433 // Now that we have all of the call sites, loop over them and inline them if
434 // it looks profitable to do so.
435 bool Changed = false;
439 // Iterate over the outer loop because inlining functions can cause indirect
440 // calls to become direct calls.
441 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
442 CallSite CS = CallSites[CSi].first;
444 Function *Caller = CS.getCaller();
445 Function *Callee = CS.getCalledFunction();
447 // If this call site is dead and it is to a readonly function, we should
448 // just delete the call instead of trying to inline it, regardless of
449 // size. This happens because IPSCCP propagates the result out of the
450 // call and then we're left with the dead call.
451 if (isInstructionTriviallyDead(CS.getInstruction())) {
452 DEBUG(dbgs() << " -> Deleting dead call: "
453 << *CS.getInstruction() << "\n");
454 // Update the call graph by deleting the edge from Callee to Caller.
455 CG[Caller]->removeCallEdgeFor(CS);
456 CS.getInstruction()->eraseFromParent();
458 // Update the cached cost info with the missing call
459 growCachedCostInfo(Caller, NULL);
461 // We can only inline direct calls to non-declarations.
462 if (Callee == 0 || Callee->isDeclaration()) continue;
464 // If this call site was obtained by inlining another function, verify
465 // that the include path for the function did not include the callee
466 // itself. If so, we'd be recursively inlining the same function,
467 // which would provide the same callsites, which would cause us to
468 // infinitely inline.
469 int InlineHistoryID = CallSites[CSi].second;
470 if (InlineHistoryID != -1 &&
471 InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory))
475 // If the policy determines that we should inline this function,
477 if (!shouldInline(CS))
480 // Attempt to inline the function.
481 if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas,
482 InlineHistoryID, InsertLifetime))
486 // If inlining this function gave us any new call sites, throw them
487 // onto our worklist to process. They are useful inline candidates.
488 if (!InlineInfo.InlinedCalls.empty()) {
489 // Create a new inline history entry for this, so that we remember
490 // that these new callsites came about due to inlining Callee.
491 int NewHistoryID = InlineHistory.size();
492 InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID));
494 for (unsigned i = 0, e = InlineInfo.InlinedCalls.size();
496 Value *Ptr = InlineInfo.InlinedCalls[i];
497 CallSite NewCS = Ptr;
498 simplifyCallSiteArguments(TD, NewCS);
499 CallSites.push_back(std::make_pair(NewCS, NewHistoryID));
503 // Update the cached cost info with the inlined call.
504 growCachedCostInfo(Caller, Callee);
507 // If we inlined or deleted the last possible call site to the function,
508 // delete the function body now.
509 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() &&
510 // TODO: Can remove if in SCC now.
511 !SCCFunctions.count(Callee) &&
513 // The function may be apparently dead, but if there are indirect
514 // callgraph references to the node, we cannot delete it yet, this
515 // could invalidate the CGSCC iterator.
516 CG[Callee]->getNumReferences() == 0) {
517 DEBUG(dbgs() << " -> Deleting dead function: "
518 << Callee->getName() << "\n");
519 CallGraphNode *CalleeNode = CG[Callee];
521 // Remove any call graph edges from the callee to its callees.
522 CalleeNode->removeAllCalledFunctions();
524 resetCachedCostInfo(Callee);
526 // Removing the node for callee from the call graph and delete it.
527 delete CG.removeFunctionFromModule(CalleeNode);
531 // Remove this call site from the list. If possible, use
532 // swap/pop_back for efficiency, but do not use it if doing so would
533 // move a call site to a function in this SCC before the
534 // 'FirstCallInSCC' barrier.
535 if (SCC.isSingular()) {
536 CallSites[CSi] = CallSites.back();
537 CallSites.pop_back();
539 CallSites.erase(CallSites.begin()+CSi);
546 } while (LocalChange);
551 // doFinalization - Remove now-dead linkonce functions at the end of
552 // processing to avoid breaking the SCC traversal.
553 bool Inliner::doFinalization(CallGraph &CG) {
554 return removeDeadFunctions(CG);
557 /// removeDeadFunctions - Remove dead functions that are not included in
558 /// DNR (Do Not Remove) list.
559 bool Inliner::removeDeadFunctions(CallGraph &CG,
560 SmallPtrSet<const Function *, 16> *DNR) {
561 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove;
563 // Scan for all of the functions, looking for ones that should now be removed
564 // from the program. Insert the dead ones in the FunctionsToRemove set.
565 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
566 CallGraphNode *CGN = I->second;
567 if (CGN->getFunction() == 0)
570 Function *F = CGN->getFunction();
572 // If the only remaining users of the function are dead constants, remove
574 F->removeDeadConstantUsers();
576 if (DNR && DNR->count(F))
578 if (!F->isDefTriviallyDead())
581 // Remove any call graph edges from the function to its callees.
582 CGN->removeAllCalledFunctions();
584 // Remove any edges from the external node to the function's call graph
585 // node. These edges might have been made irrelegant due to
586 // optimization of the program.
587 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
589 // Removing the node for callee from the call graph and delete it.
590 FunctionsToRemove.insert(CGN);
593 // Now that we know which functions to delete, do so. We didn't want to do
594 // this inline, because that would invalidate our CallGraph::iterator
597 // Note that it doesn't matter that we are iterating over a non-stable set
598 // here to do this, it doesn't matter which order the functions are deleted
600 bool Changed = false;
601 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(),
602 E = FunctionsToRemove.end(); I != E; ++I) {
603 resetCachedCostInfo((*I)->getFunction());
604 delete CG.removeFunctionFromModule(*I);