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/Target/TargetData.h"
23 #include "llvm/Transforms/IPO/InlinerPass.h"
24 #include "llvm/Transforms/Utils/Cloning.h"
25 #include "llvm/Transforms/Utils/Local.h"
26 #include "llvm/Support/CallSite.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #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) {}
54 Inliner::Inliner(char &ID, int Threshold)
55 : CallGraphSCCPass(ID), InlineThreshold(Threshold) {}
57 /// getAnalysisUsage - For this class, we declare that we require and preserve
58 /// the call graph. If the derived class implements this method, it should
59 /// always explicitly call the implementation here.
60 void Inliner::getAnalysisUsage(AnalysisUsage &Info) const {
61 CallGraphSCCPass::getAnalysisUsage(Info);
65 typedef DenseMap<const ArrayType*, std::vector<AllocaInst*> >
66 InlinedArrayAllocasTy;
68 /// InlineCallIfPossible - If it is possible to inline the specified call site,
69 /// do so and update the CallGraph for this operation.
71 /// This function also does some basic book-keeping to update the IR. The
72 /// InlinedArrayAllocas map keeps track of any allocas that are already
73 /// available from other functions inlined into the caller. If we are able to
74 /// inline this call site we attempt to reuse already available allocas or add
75 /// any new allocas to the set if not possible.
76 static bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI,
77 InlinedArrayAllocasTy &InlinedArrayAllocas) {
78 Function *Callee = CS.getCalledFunction();
79 Function *Caller = CS.getCaller();
81 // Try to inline the function. Get the list of static allocas that were
83 if (!InlineFunction(CS, IFI))
86 // If the inlined function had a higher stack protection level than the
87 // calling function, then bump up the caller's stack protection level.
88 if (Callee->hasFnAttr(Attribute::StackProtectReq))
89 Caller->addFnAttr(Attribute::StackProtectReq);
90 else if (Callee->hasFnAttr(Attribute::StackProtect) &&
91 !Caller->hasFnAttr(Attribute::StackProtectReq))
92 Caller->addFnAttr(Attribute::StackProtect);
95 // Look at all of the allocas that we inlined through this call site. If we
96 // have already inlined other allocas through other calls into this function,
97 // then we know that they have disjoint lifetimes and that we can merge them.
99 // There are many heuristics possible for merging these allocas, and the
100 // different options have different tradeoffs. One thing that we *really*
101 // don't want to hurt is SRoA: once inlining happens, often allocas are no
102 // longer address taken and so they can be promoted.
104 // Our "solution" for that is to only merge allocas whose outermost type is an
105 // array type. These are usually not promoted because someone is using a
106 // variable index into them. These are also often the most important ones to
109 // A better solution would be to have real memory lifetime markers in the IR
110 // and not have the inliner do any merging of allocas at all. This would
111 // allow the backend to do proper stack slot coloring of all allocas that
112 // *actually make it to the backend*, which is really what we want.
114 // Because we don't have this information, we do this simple and useful hack.
116 SmallPtrSet<AllocaInst*, 16> UsedAllocas;
118 // Loop over all the allocas we have so far and see if they can be merged with
119 // a previously inlined alloca. If not, remember that we had it.
120 for (unsigned AllocaNo = 0, e = IFI.StaticAllocas.size();
121 AllocaNo != e; ++AllocaNo) {
122 AllocaInst *AI = IFI.StaticAllocas[AllocaNo];
124 // Don't bother trying to merge array allocations (they will usually be
125 // canonicalized to be an allocation *of* an array), or allocations whose
126 // type is not itself an array (because we're afraid of pessimizing SRoA).
127 const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType());
128 if (ATy == 0 || AI->isArrayAllocation())
131 // Get the list of all available allocas for this array type.
132 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy];
134 // Loop over the allocas in AllocasForType to see if we can reuse one. Note
135 // that we have to be careful not to reuse the same "available" alloca for
136 // multiple different allocas that we just inlined, we use the 'UsedAllocas'
137 // set to keep track of which "available" allocas are being used by this
138 // function. Also, AllocasForType can be empty of course!
139 bool MergedAwayAlloca = false;
140 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) {
141 AllocaInst *AvailableAlloca = AllocasForType[i];
143 // The available alloca has to be in the right function, not in some other
144 // function in this SCC.
145 if (AvailableAlloca->getParent() != AI->getParent())
148 // If the inlined function already uses this alloca then we can't reuse
150 if (!UsedAllocas.insert(AvailableAlloca))
153 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare
155 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI);
157 AI->replaceAllUsesWith(AvailableAlloca);
158 AI->eraseFromParent();
159 MergedAwayAlloca = true;
164 // If we already nuked the alloca, we're done with it.
165 if (MergedAwayAlloca)
168 // If we were unable to merge away the alloca either because there are no
169 // allocas of the right type available or because we reused them all
170 // already, remember that this alloca came from an inlined function and mark
171 // it used so we don't reuse it for other allocas from this inline
173 AllocasForType.push_back(AI);
174 UsedAllocas.insert(AI);
180 unsigned Inliner::getInlineThreshold(CallSite CS) const {
181 int thres = InlineThreshold;
183 // Listen to optsize when -inline-limit is not given.
184 Function *Caller = CS.getCaller();
185 if (Caller && !Caller->isDeclaration() &&
186 Caller->hasFnAttr(Attribute::OptimizeForSize) &&
187 InlineLimit.getNumOccurrences() == 0)
188 thres = OptSizeThreshold;
190 // Listen to inlinehint when it would increase the threshold.
191 Function *Callee = CS.getCalledFunction();
192 if (HintThreshold > thres && Callee && !Callee->isDeclaration() &&
193 Callee->hasFnAttr(Attribute::InlineHint))
194 thres = HintThreshold;
199 /// shouldInline - Return true if the inliner should attempt to inline
200 /// at the given CallSite.
201 bool Inliner::shouldInline(CallSite CS) {
202 InlineCost IC = getInlineCost(CS);
205 DEBUG(dbgs() << " Inlining: cost=always"
206 << ", Call: " << *CS.getInstruction() << "\n");
211 DEBUG(dbgs() << " NOT Inlining: cost=never"
212 << ", Call: " << *CS.getInstruction() << "\n");
216 int Cost = IC.getValue();
217 Function *Caller = CS.getCaller();
218 int CurrentThreshold = getInlineThreshold(CS);
219 float FudgeFactor = getInlineFudgeFactor(CS);
220 int AdjThreshold = (int)(CurrentThreshold * FudgeFactor);
221 if (Cost >= AdjThreshold) {
222 DEBUG(dbgs() << " NOT Inlining: cost=" << Cost
223 << ", thres=" << AdjThreshold
224 << ", Call: " << *CS.getInstruction() << "\n");
228 // Try to detect the case where the current inlining candidate caller
229 // (call it B) is a static function and is an inlining candidate elsewhere,
230 // and the current candidate callee (call it C) is large enough that
231 // inlining it into B would make B too big to inline later. In these
232 // circumstances it may be best not to inline C into B, but to inline B
234 if (Caller->hasLocalLinkage()) {
235 int TotalSecondaryCost = 0;
236 bool outerCallsFound = false;
237 bool allOuterCallsWillBeInlined = true;
238 bool someOuterCallWouldNotBeInlined = false;
239 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end();
243 // If this isn't a call to Caller (it could be some other sort
244 // of reference) skip it.
245 if (!CS2 || CS2.getCalledFunction() != Caller)
248 InlineCost IC2 = getInlineCost(CS2);
250 allOuterCallsWillBeInlined = false;
251 if (IC2.isAlways() || IC2.isNever())
254 outerCallsFound = true;
255 int Cost2 = IC2.getValue();
256 int CurrentThreshold2 = getInlineThreshold(CS2);
257 float FudgeFactor2 = getInlineFudgeFactor(CS2);
259 if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2))
260 allOuterCallsWillBeInlined = false;
262 // See if we have this case. We subtract off the penalty
263 // for the call instruction, which we would be deleting.
264 if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) &&
265 Cost2 + Cost - (InlineConstants::CallPenalty + 1) >=
266 (int)(CurrentThreshold2 * FudgeFactor2)) {
267 someOuterCallWouldNotBeInlined = true;
268 TotalSecondaryCost += Cost2;
271 // If all outer calls to Caller would get inlined, the cost for the last
272 // one is set very low by getInlineCost, in anticipation that Caller will
273 // be removed entirely. We did not account for this above unless there
274 // is only one caller of Caller.
275 if (allOuterCallsWillBeInlined && Caller->use_begin() != Caller->use_end())
276 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus;
278 if (outerCallsFound && someOuterCallWouldNotBeInlined &&
279 TotalSecondaryCost < Cost) {
280 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() <<
281 " Cost = " << Cost <<
282 ", outer Cost = " << TotalSecondaryCost << '\n');
287 DEBUG(dbgs() << " Inlining: cost=" << Cost
288 << ", thres=" << AdjThreshold
289 << ", Call: " << *CS.getInstruction() << '\n');
293 /// InlineHistoryIncludes - Return true if the specified inline history ID
294 /// indicates an inline history that includes the specified function.
295 static bool InlineHistoryIncludes(Function *F, int InlineHistoryID,
296 const SmallVectorImpl<std::pair<Function*, int> > &InlineHistory) {
297 while (InlineHistoryID != -1) {
298 assert(unsigned(InlineHistoryID) < InlineHistory.size() &&
299 "Invalid inline history ID");
300 if (InlineHistory[InlineHistoryID].first == F)
302 InlineHistoryID = InlineHistory[InlineHistoryID].second;
308 bool Inliner::runOnSCC(CallGraphSCC &SCC) {
309 CallGraph &CG = getAnalysis<CallGraph>();
310 const TargetData *TD = getAnalysisIfAvailable<TargetData>();
312 SmallPtrSet<Function*, 8> SCCFunctions;
313 DEBUG(dbgs() << "Inliner visiting SCC:");
314 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
315 Function *F = (*I)->getFunction();
316 if (F) SCCFunctions.insert(F);
317 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE"));
320 // Scan through and identify all call sites ahead of time so that we only
321 // inline call sites in the original functions, not call sites that result
322 // from inlining other functions.
323 SmallVector<std::pair<CallSite, int>, 16> CallSites;
325 // When inlining a callee produces new call sites, we want to keep track of
326 // the fact that they were inlined from the callee. This allows us to avoid
327 // infinite inlining in some obscure cases. To represent this, we use an
328 // index into the InlineHistory vector.
329 SmallVector<std::pair<Function*, int>, 8> InlineHistory;
331 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
332 Function *F = (*I)->getFunction();
335 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
336 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
337 CallSite CS(cast<Value>(I));
338 // If this isn't a call, or it is a call to an intrinsic, it can
340 if (!CS || isa<IntrinsicInst>(I))
343 // If this is a direct call to an external function, we can never inline
344 // it. If it is an indirect call, inlining may resolve it to be a
345 // direct call, so we keep it.
346 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration())
349 CallSites.push_back(std::make_pair(CS, -1));
353 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n");
355 // If there are no calls in this function, exit early.
356 if (CallSites.empty())
359 // Now that we have all of the call sites, move the ones to functions in the
360 // current SCC to the end of the list.
361 unsigned FirstCallInSCC = CallSites.size();
362 for (unsigned i = 0; i < FirstCallInSCC; ++i)
363 if (Function *F = CallSites[i].first.getCalledFunction())
364 if (SCCFunctions.count(F))
365 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
368 InlinedArrayAllocasTy InlinedArrayAllocas;
369 InlineFunctionInfo InlineInfo(&CG, TD);
371 // Now that we have all of the call sites, loop over them and inline them if
372 // it looks profitable to do so.
373 bool Changed = false;
377 // Iterate over the outer loop because inlining functions can cause indirect
378 // calls to become direct calls.
379 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
380 CallSite CS = CallSites[CSi].first;
382 Function *Caller = CS.getCaller();
383 Function *Callee = CS.getCalledFunction();
385 // If this call site is dead and it is to a readonly function, we should
386 // just delete the call instead of trying to inline it, regardless of
387 // size. This happens because IPSCCP propagates the result out of the
388 // call and then we're left with the dead call.
389 if (isInstructionTriviallyDead(CS.getInstruction())) {
390 DEBUG(dbgs() << " -> Deleting dead call: "
391 << *CS.getInstruction() << "\n");
392 // Update the call graph by deleting the edge from Callee to Caller.
393 CG[Caller]->removeCallEdgeFor(CS);
394 CS.getInstruction()->eraseFromParent();
396 // Update the cached cost info with the missing call
397 growCachedCostInfo(Caller, NULL);
399 // We can only inline direct calls to non-declarations.
400 if (Callee == 0 || Callee->isDeclaration()) continue;
402 // If this call site was obtained by inlining another function, verify
403 // that the include path for the function did not include the callee
404 // itself. If so, we'd be recursively inlinling the same function,
405 // which would provide the same callsites, which would cause us to
406 // infinitely inline.
407 int InlineHistoryID = CallSites[CSi].second;
408 if (InlineHistoryID != -1 &&
409 InlineHistoryIncludes(Callee, InlineHistoryID, InlineHistory))
413 // If the policy determines that we should inline this function,
415 if (!shouldInline(CS))
418 // Attempt to inline the function.
419 if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas))
423 // If inlining this function gave us any new call sites, throw them
424 // onto our worklist to process. They are useful inline candidates.
425 if (!InlineInfo.InlinedCalls.empty()) {
426 // Create a new inline history entry for this, so that we remember
427 // that these new callsites came about due to inlining Callee.
428 int NewHistoryID = InlineHistory.size();
429 InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID));
431 for (unsigned i = 0, e = InlineInfo.InlinedCalls.size();
433 Value *Ptr = InlineInfo.InlinedCalls[i];
434 CallSites.push_back(std::make_pair(CallSite(Ptr), NewHistoryID));
438 // Update the cached cost info with the inlined call.
439 growCachedCostInfo(Caller, Callee);
442 // If we inlined or deleted the last possible call site to the function,
443 // delete the function body now.
444 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() &&
445 // TODO: Can remove if in SCC now.
446 !SCCFunctions.count(Callee) &&
448 // The function may be apparently dead, but if there are indirect
449 // callgraph references to the node, we cannot delete it yet, this
450 // could invalidate the CGSCC iterator.
451 CG[Callee]->getNumReferences() == 0) {
452 DEBUG(dbgs() << " -> Deleting dead function: "
453 << Callee->getName() << "\n");
454 CallGraphNode *CalleeNode = CG[Callee];
456 // Remove any call graph edges from the callee to its callees.
457 CalleeNode->removeAllCalledFunctions();
459 resetCachedCostInfo(Callee);
461 // Removing the node for callee from the call graph and delete it.
462 delete CG.removeFunctionFromModule(CalleeNode);
466 // Remove this call site from the list. If possible, use
467 // swap/pop_back for efficiency, but do not use it if doing so would
468 // move a call site to a function in this SCC before the
469 // 'FirstCallInSCC' barrier.
470 if (SCC.isSingular()) {
471 CallSites[CSi] = CallSites.back();
472 CallSites.pop_back();
474 CallSites.erase(CallSites.begin()+CSi);
481 } while (LocalChange);
486 // doFinalization - Remove now-dead linkonce functions at the end of
487 // processing to avoid breaking the SCC traversal.
488 bool Inliner::doFinalization(CallGraph &CG) {
489 return removeDeadFunctions(CG);
492 /// removeDeadFunctions - Remove dead functions that are not included in
493 /// DNR (Do Not Remove) list.
494 bool Inliner::removeDeadFunctions(CallGraph &CG,
495 SmallPtrSet<const Function *, 16> *DNR) {
496 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove;
498 // Scan for all of the functions, looking for ones that should now be removed
499 // from the program. Insert the dead ones in the FunctionsToRemove set.
500 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
501 CallGraphNode *CGN = I->second;
502 if (CGN->getFunction() == 0)
505 Function *F = CGN->getFunction();
507 // If the only remaining users of the function are dead constants, remove
509 F->removeDeadConstantUsers();
511 if (DNR && DNR->count(F))
513 if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() &&
514 !F->hasAvailableExternallyLinkage())
519 // Remove any call graph edges from the function to its callees.
520 CGN->removeAllCalledFunctions();
522 // Remove any edges from the external node to the function's call graph
523 // node. These edges might have been made irrelegant due to
524 // optimization of the program.
525 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
527 // Removing the node for callee from the call graph and delete it.
528 FunctionsToRemove.insert(CGN);
531 // Now that we know which functions to delete, do so. We didn't want to do
532 // this inline, because that would invalidate our CallGraph::iterator
535 // Note that it doesn't matter that we are iterating over a non-stable set
536 // here to do this, it doesn't matter which order the functions are deleted
538 bool Changed = false;
539 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(),
540 E = FunctionsToRemove.end(); I != E; ++I) {
541 resetCachedCostInfo((*I)->getFunction());
542 delete CG.removeFunctionFromModule(*I);