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(void *ID)
52 : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {}
54 Inliner::Inliner(void *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, CallGraph &CG,
78 InlinedArrayAllocasTy &InlinedArrayAllocas) {
79 Function *Callee = CS.getCalledFunction();
80 Function *Caller = CS.getCaller();
82 // Try to inline the function. Get the list of static allocas that were
84 SmallVector<AllocaInst*, 16> StaticAllocas;
85 if (!InlineFunction(CS, &CG, TD, &StaticAllocas))
88 // If the inlined function had a higher stack protection level than the
89 // calling function, then bump up the caller's stack protection level.
90 if (Callee->hasFnAttr(Attribute::StackProtectReq))
91 Caller->addFnAttr(Attribute::StackProtectReq);
92 else if (Callee->hasFnAttr(Attribute::StackProtect) &&
93 !Caller->hasFnAttr(Attribute::StackProtectReq))
94 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 // Loop over all the allocas we have so far and see if they can be merged with
121 // a previously inlined alloca. If not, remember that we had it.
122 for (unsigned AllocaNo = 0, e = StaticAllocas.size();
123 AllocaNo != e; ++AllocaNo) {
124 AllocaInst *AI = StaticAllocas[AllocaNo];
126 // Don't bother trying to merge array allocations (they will usually be
127 // canonicalized to be an allocation *of* an array), or allocations whose
128 // type is not itself an array (because we're afraid of pessimizing SRoA).
129 const ArrayType *ATy = dyn_cast<ArrayType>(AI->getAllocatedType());
130 if (ATy == 0 || AI->isArrayAllocation())
133 // Get the list of all available allocas for this array type.
134 std::vector<AllocaInst*> &AllocasForType = InlinedArrayAllocas[ATy];
136 // Loop over the allocas in AllocasForType to see if we can reuse one. Note
137 // that we have to be careful not to reuse the same "available" alloca for
138 // multiple different allocas that we just inlined, we use the 'UsedAllocas'
139 // set to keep track of which "available" allocas are being used by this
140 // function. Also, AllocasForType can be empty of course!
141 bool MergedAwayAlloca = false;
142 for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) {
143 AllocaInst *AvailableAlloca = AllocasForType[i];
145 // The available alloca has to be in the right function, not in some other
146 // function in this SCC.
147 if (AvailableAlloca->getParent() != AI->getParent())
150 // If the inlined function already uses this alloca then we can't reuse
152 if (!UsedAllocas.insert(AvailableAlloca))
155 // Otherwise, we *can* reuse it, RAUW AI into AvailableAlloca and declare
157 DEBUG(dbgs() << " ***MERGED ALLOCA: " << *AI);
159 AI->replaceAllUsesWith(AvailableAlloca);
160 AI->eraseFromParent();
161 MergedAwayAlloca = true;
166 // If we already nuked the alloca, we're done with it.
167 if (MergedAwayAlloca)
170 // If we were unable to merge away the alloca either because there are no
171 // allocas of the right type available or because we reused them all
172 // already, remember that this alloca came from an inlined function and mark
173 // it used so we don't reuse it for other allocas from this inline
175 AllocasForType.push_back(AI);
176 UsedAllocas.insert(AI);
182 unsigned Inliner::getInlineThreshold(CallSite CS) const {
183 int thres = InlineThreshold;
185 // Listen to optsize when -inline-limit is not given.
186 Function *Caller = CS.getCaller();
187 if (Caller && !Caller->isDeclaration() &&
188 Caller->hasFnAttr(Attribute::OptimizeForSize) &&
189 InlineLimit.getNumOccurrences() == 0)
190 thres = OptSizeThreshold;
192 // Listen to inlinehint when it would increase the threshold.
193 Function *Callee = CS.getCalledFunction();
194 if (HintThreshold > thres && Callee && !Callee->isDeclaration() &&
195 Callee->hasFnAttr(Attribute::InlineHint))
196 thres = HintThreshold;
201 /// shouldInline - Return true if the inliner should attempt to inline
202 /// at the given CallSite.
203 bool Inliner::shouldInline(CallSite CS) {
204 InlineCost IC = getInlineCost(CS);
207 DEBUG(dbgs() << " Inlining: cost=always"
208 << ", Call: " << *CS.getInstruction() << "\n");
213 DEBUG(dbgs() << " NOT Inlining: cost=never"
214 << ", Call: " << *CS.getInstruction() << "\n");
218 int Cost = IC.getValue();
219 Function *Caller = CS.getCaller();
220 int CurrentThreshold = getInlineThreshold(CS);
221 float FudgeFactor = getInlineFudgeFactor(CS);
222 int AdjThreshold = (int)(CurrentThreshold * FudgeFactor);
223 if (Cost >= AdjThreshold) {
224 DEBUG(dbgs() << " NOT Inlining: cost=" << Cost
225 << ", thres=" << AdjThreshold
226 << ", Call: " << *CS.getInstruction() << "\n");
230 // Try to detect the case where the current inlining candidate caller
231 // (call it B) is a static function and is an inlining candidate elsewhere,
232 // and the current candidate callee (call it C) is large enough that
233 // inlining it into B would make B too big to inline later. In these
234 // circumstances it may be best not to inline C into B, but to inline B
236 if (Caller->hasLocalLinkage()) {
237 int TotalSecondaryCost = 0;
238 bool outerCallsFound = false;
239 bool allOuterCallsWillBeInlined = true;
240 bool someOuterCallWouldNotBeInlined = false;
241 for (Value::use_iterator I = Caller->use_begin(), E =Caller->use_end();
243 CallSite CS2 = CallSite::get(*I);
245 // If this isn't a call to Caller (it could be some other sort
246 // of reference) skip it.
247 if (CS2.getInstruction() == 0 || CS2.getCalledFunction() != Caller)
250 InlineCost IC2 = getInlineCost(CS2);
252 allOuterCallsWillBeInlined = false;
253 if (IC2.isAlways() || IC2.isNever())
256 outerCallsFound = true;
257 int Cost2 = IC2.getValue();
258 int CurrentThreshold2 = getInlineThreshold(CS2);
259 float FudgeFactor2 = getInlineFudgeFactor(CS2);
261 if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2))
262 allOuterCallsWillBeInlined = false;
264 // See if we have this case. We subtract off the penalty
265 // for the call instruction, which we would be deleting.
266 if (Cost2 < (int)(CurrentThreshold2 * FudgeFactor2) &&
267 Cost2 + Cost - (InlineConstants::CallPenalty + 1) >=
268 (int)(CurrentThreshold2 * FudgeFactor2)) {
269 someOuterCallWouldNotBeInlined = true;
270 TotalSecondaryCost += Cost2;
273 // If all outer calls to Caller would get inlined, the cost for the last
274 // one is set very low by getInlineCost, in anticipation that Caller will
275 // be removed entirely. We did not account for this above unless there
276 // is only one caller of Caller.
277 if (allOuterCallsWillBeInlined && Caller->use_begin() != Caller->use_end())
278 TotalSecondaryCost += InlineConstants::LastCallToStaticBonus;
280 if (outerCallsFound && someOuterCallWouldNotBeInlined &&
281 TotalSecondaryCost < Cost) {
282 DEBUG(dbgs() << " NOT Inlining: " << *CS.getInstruction() <<
283 " Cost = " << Cost <<
284 ", outer Cost = " << TotalSecondaryCost << '\n');
289 DEBUG(dbgs() << " Inlining: cost=" << Cost
290 << ", thres=" << AdjThreshold
291 << ", Call: " << *CS.getInstruction() << '\n');
295 bool Inliner::runOnSCC(CallGraphSCC &SCC) {
296 CallGraph &CG = getAnalysis<CallGraph>();
297 const TargetData *TD = getAnalysisIfAvailable<TargetData>();
299 SmallPtrSet<Function*, 8> SCCFunctions;
300 DEBUG(dbgs() << "Inliner visiting SCC:");
301 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
302 Function *F = (*I)->getFunction();
303 if (F) SCCFunctions.insert(F);
304 DEBUG(dbgs() << " " << (F ? F->getName() : "INDIRECTNODE"));
307 // Scan through and identify all call sites ahead of time so that we only
308 // inline call sites in the original functions, not call sites that result
309 // from inlining other functions.
310 SmallVector<CallSite, 16> CallSites;
312 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
313 Function *F = (*I)->getFunction();
316 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
317 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
318 CallSite CS = CallSite::get(I);
319 // If this isn't a call, or it is a call to an intrinsic, it can
321 if (CS.getInstruction() == 0 || isa<IntrinsicInst>(I))
324 // If this is a direct call to an external function, we can never inline
325 // it. If it is an indirect call, inlining may resolve it to be a
326 // direct call, so we keep it.
327 if (CS.getCalledFunction() && CS.getCalledFunction()->isDeclaration())
330 CallSites.push_back(CS);
334 DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n");
336 // Now that we have all of the call sites, move the ones to functions in the
337 // current SCC to the end of the list.
338 unsigned FirstCallInSCC = CallSites.size();
339 for (unsigned i = 0; i < FirstCallInSCC; ++i)
340 if (Function *F = CallSites[i].getCalledFunction())
341 if (SCCFunctions.count(F))
342 std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
345 InlinedArrayAllocasTy InlinedArrayAllocas;
347 // Now that we have all of the call sites, loop over them and inline them if
348 // it looks profitable to do so.
349 bool Changed = false;
353 // Iterate over the outer loop because inlining functions can cause indirect
354 // calls to become direct calls.
355 for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
356 CallSite CS = CallSites[CSi];
358 Function *Caller = CS.getCaller();
359 Function *Callee = CS.getCalledFunction();
361 // If this call site is dead and it is to a readonly function, we should
362 // just delete the call instead of trying to inline it, regardless of
363 // size. This happens because IPSCCP propagates the result out of the
364 // call and then we're left with the dead call.
365 if (isInstructionTriviallyDead(CS.getInstruction())) {
366 DEBUG(dbgs() << " -> Deleting dead call: "
367 << *CS.getInstruction() << "\n");
368 // Update the call graph by deleting the edge from Callee to Caller.
369 CG[Caller]->removeCallEdgeFor(CS);
370 CS.getInstruction()->eraseFromParent();
372 // Update the cached cost info with the missing call
373 growCachedCostInfo(Caller, NULL);
375 // We can only inline direct calls to non-declarations.
376 if (Callee == 0 || Callee->isDeclaration()) continue;
378 // If the policy determines that we should inline this function,
380 if (!shouldInline(CS))
383 // Attempt to inline the function...
384 if (!InlineCallIfPossible(CS, CG, TD, InlinedArrayAllocas))
388 // Update the cached cost info with the inlined call.
389 growCachedCostInfo(Caller, Callee);
392 // If we inlined or deleted the last possible call site to the function,
393 // delete the function body now.
394 if (Callee && Callee->use_empty() && Callee->hasLocalLinkage() &&
395 // TODO: Can remove if in SCC now.
396 !SCCFunctions.count(Callee) &&
398 // The function may be apparently dead, but if there are indirect
399 // callgraph references to the node, we cannot delete it yet, this
400 // could invalidate the CGSCC iterator.
401 CG[Callee]->getNumReferences() == 0) {
402 DEBUG(dbgs() << " -> Deleting dead function: "
403 << Callee->getName() << "\n");
404 CallGraphNode *CalleeNode = CG[Callee];
406 // Remove any call graph edges from the callee to its callees.
407 CalleeNode->removeAllCalledFunctions();
409 resetCachedCostInfo(Callee);
411 // Removing the node for callee from the call graph and delete it.
412 delete CG.removeFunctionFromModule(CalleeNode);
416 // Remove this call site from the list. If possible, use
417 // swap/pop_back for efficiency, but do not use it if doing so would
418 // move a call site to a function in this SCC before the
419 // 'FirstCallInSCC' barrier.
420 if (SCC.isSingular()) {
421 std::swap(CallSites[CSi], CallSites.back());
422 CallSites.pop_back();
424 CallSites.erase(CallSites.begin()+CSi);
431 } while (LocalChange);
436 // doFinalization - Remove now-dead linkonce functions at the end of
437 // processing to avoid breaking the SCC traversal.
438 bool Inliner::doFinalization(CallGraph &CG) {
439 return removeDeadFunctions(CG);
442 /// removeDeadFunctions - Remove dead functions that are not included in
443 /// DNR (Do Not Remove) list.
444 bool Inliner::removeDeadFunctions(CallGraph &CG,
445 SmallPtrSet<const Function *, 16> *DNR) {
446 SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove;
448 // Scan for all of the functions, looking for ones that should now be removed
449 // from the program. Insert the dead ones in the FunctionsToRemove set.
450 for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
451 CallGraphNode *CGN = I->second;
452 if (CGN->getFunction() == 0)
455 Function *F = CGN->getFunction();
457 // If the only remaining users of the function are dead constants, remove
459 F->removeDeadConstantUsers();
461 if (DNR && DNR->count(F))
463 if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() &&
464 !F->hasAvailableExternallyLinkage())
469 // Remove any call graph edges from the function to its callees.
470 CGN->removeAllCalledFunctions();
472 // Remove any edges from the external node to the function's call graph
473 // node. These edges might have been made irrelegant due to
474 // optimization of the program.
475 CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
477 // Removing the node for callee from the call graph and delete it.
478 FunctionsToRemove.insert(CGN);
481 // Now that we know which functions to delete, do so. We didn't want to do
482 // this inline, because that would invalidate our CallGraph::iterator
485 // Note that it doesn't matter that we are iterating over a non-stable set
486 // here to do this, it doesn't matter which order the functions are deleted
488 bool Changed = false;
489 for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(),
490 E = FunctionsToRemove.end(); I != E; ++I) {
491 resetCachedCostInfo((*I)->getFunction());
492 delete CG.removeFunctionFromModule(*I);