1 //===- InlineCost.cpp - Cost analysis for inliner -------------------------===//
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 inline cost analysis.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Analysis/InlineCost.h"
15 #include "llvm/Support/CallSite.h"
16 #include "llvm/CallingConv.h"
17 #include "llvm/IntrinsicInst.h"
18 #include "llvm/ADT/SmallPtrSet.h"
21 // CountCodeReductionForConstant - Figure out an approximation for how many
22 // instructions will be constant folded if the specified value is constant.
24 unsigned InlineCostAnalyzer::FunctionInfo::
25 CountCodeReductionForConstant(Value *V) {
26 unsigned Reduction = 0;
27 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
28 if (isa<BranchInst>(*UI))
29 Reduction += 40; // Eliminating a conditional branch is a big win
30 else if (SwitchInst *SI = dyn_cast<SwitchInst>(*UI))
31 // Eliminating a switch is a big win, proportional to the number of edges
33 Reduction += (SI->getNumSuccessors()-1) * 40;
34 else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
35 // Turning an indirect call into a direct call is a BIG win
36 Reduction += CI->getCalledValue() == V ? 500 : 0;
37 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
38 // Turning an indirect call into a direct call is a BIG win
39 Reduction += II->getCalledValue() == V ? 500 : 0;
41 // Figure out if this instruction will be removed due to simple constant
43 Instruction &Inst = cast<Instruction>(**UI);
45 // We can't constant propagate instructions which have effects or
48 // FIXME: It would be nice to capture the fact that a load from a
49 // pointer-to-constant-global is actually a *really* good thing to zap.
50 // Unfortunately, we don't know the pointer that may get propagated here,
51 // so we can't make this decision.
52 if (Inst.mayReadFromMemory() || Inst.mayHaveSideEffects() ||
53 isa<AllocationInst>(Inst))
56 bool AllOperandsConstant = true;
57 for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i)
58 if (!isa<Constant>(Inst.getOperand(i)) && Inst.getOperand(i) != V) {
59 AllOperandsConstant = false;
63 if (AllOperandsConstant) {
64 // We will get to remove this instruction...
67 // And any other instructions that use it which become constants
69 Reduction += CountCodeReductionForConstant(&Inst);
76 // CountCodeReductionForAlloca - Figure out an approximation of how much smaller
77 // the function will be if it is inlined into a context where an argument
80 unsigned InlineCostAnalyzer::FunctionInfo::
81 CountCodeReductionForAlloca(Value *V) {
82 if (!isa<PointerType>(V->getType())) return 0; // Not a pointer
83 unsigned Reduction = 0;
84 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
85 Instruction *I = cast<Instruction>(*UI);
86 if (isa<LoadInst>(I) || isa<StoreInst>(I))
88 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
89 // If the GEP has variable indices, we won't be able to do much with it.
90 if (!GEP->hasAllConstantIndices())
91 Reduction += CountCodeReductionForAlloca(GEP)+15;
93 // If there is some other strange instruction, we're not going to be able
94 // to do much if we inline this.
102 /// analyzeBasicBlock - Fill in the current structure with information gleaned
103 /// from the specified block.
104 void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB) {
107 for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
109 if (isa<PHINode>(II)) continue; // PHI nodes don't count.
111 // Special handling for calls.
112 if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
113 if (isa<DbgInfoIntrinsic>(II))
114 continue; // Debug intrinsics don't count as size.
116 CallSite CS = CallSite::get(const_cast<Instruction*>(&*II));
118 // If this function contains a call to setjmp or _setjmp, never inline
119 // it. This is a hack because we depend on the user marking their local
120 // variables as volatile if they are live across a setjmp call, and they
121 // probably won't do this in callers.
122 if (Function *F = CS.getCalledFunction())
123 if (F->isDeclaration() &&
124 (F->getName() == "setjmp" || F->getName() == "_setjmp")) {
129 // Calls often compile into many machine instructions. Bump up their
130 // cost to reflect this.
131 if (!isa<IntrinsicInst>(II))
132 NumInsts += InlineConstants::CallPenalty;
135 // These, too, are calls.
136 if (isa<MallocInst>(II) || isa<FreeInst>(II))
137 NumInsts += InlineConstants::CallPenalty;
139 if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
140 if (!AI->isStaticAlloca())
141 this->usesDynamicAlloca = true;
144 if (isa<ExtractElementInst>(II) || isa<VectorType>(II->getType()))
147 // Noop casts, including ptr <-> int, don't count.
148 if (const CastInst *CI = dyn_cast<CastInst>(II)) {
149 if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) ||
150 isa<PtrToIntInst>(CI))
152 } else if (const GetElementPtrInst *GEPI =
153 dyn_cast<GetElementPtrInst>(II)) {
154 // If a GEP has all constant indices, it will probably be folded with
156 if (GEPI->hasAllConstantIndices())
160 if (isa<ReturnInst>(II))
167 /// analyzeFunction - Fill in the current structure with information gleaned
168 /// from the specified function.
169 void CodeMetrics::analyzeFunction(Function *F) {
170 // Look at the size of the callee.
171 for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
172 analyzeBasicBlock(&*BB);
175 /// analyzeFunction - Fill in the current structure with information gleaned
176 /// from the specified function.
177 void InlineCostAnalyzer::FunctionInfo::analyzeFunction(Function *F) {
178 Metrics.analyzeFunction(F);
180 // A function with exactly one return has it removed during the inlining
181 // process (see InlineFunction), so don't count it.
182 // FIXME: This knowledge should really be encoded outside of FunctionInfo.
183 if (Metrics.NumRets==1)
186 // Check out all of the arguments to the function, figuring out how much
187 // code can be eliminated if one of the arguments is a constant.
188 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
189 ArgumentWeights.push_back(ArgInfo(CountCodeReductionForConstant(I),
190 CountCodeReductionForAlloca(I)));
193 // getInlineCost - The heuristic used to determine if we should inline the
194 // function call or not.
196 InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS,
197 SmallPtrSet<const Function *, 16> &NeverInline) {
198 Instruction *TheCall = CS.getInstruction();
199 Function *Callee = CS.getCalledFunction();
200 Function *Caller = TheCall->getParent()->getParent();
202 // Don't inline functions which can be redefined at link-time to mean
203 // something else. Don't inline functions marked noinline.
204 if (Callee->mayBeOverridden() ||
205 Callee->hasFnAttr(Attribute::NoInline) || NeverInline.count(Callee))
206 return llvm::InlineCost::getNever();
208 // InlineCost - This value measures how good of an inline candidate this call
209 // site is to inline. A lower inline cost make is more likely for the call to
210 // be inlined. This value may go negative.
214 // If there is only one call of the function, and it has internal linkage,
215 // make it almost guaranteed to be inlined.
217 if (Callee->hasLocalLinkage() && Callee->hasOneUse())
218 InlineCost += InlineConstants::LastCallToStaticBonus;
220 // If this function uses the coldcc calling convention, prefer not to inline
222 if (Callee->getCallingConv() == CallingConv::Cold)
223 InlineCost += InlineConstants::ColdccPenalty;
225 // If the instruction after the call, or if the normal destination of the
226 // invoke is an unreachable instruction, the function is noreturn. As such,
227 // there is little point in inlining this.
228 if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) {
229 if (isa<UnreachableInst>(II->getNormalDest()->begin()))
230 InlineCost += InlineConstants::NoreturnPenalty;
231 } else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall)))
232 InlineCost += InlineConstants::NoreturnPenalty;
234 // Get information about the callee...
235 FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
237 // If we haven't calculated this information yet, do so now.
238 if (CalleeFI.Metrics.NumBlocks == 0)
239 CalleeFI.analyzeFunction(Callee);
241 // If we should never inline this, return a huge cost.
242 if (CalleeFI.Metrics.NeverInline)
243 return InlineCost::getNever();
245 // FIXME: It would be nice to kill off CalleeFI.NeverInline. Then we
246 // could move this up and avoid computing the FunctionInfo for
247 // things we are going to just return always inline for. This
248 // requires handling setjmp somewhere else, however.
249 if (!Callee->isDeclaration() && Callee->hasFnAttr(Attribute::AlwaysInline))
250 return InlineCost::getAlways();
252 if (CalleeFI.Metrics.usesDynamicAlloca) {
253 // Get infomation about the caller...
254 FunctionInfo &CallerFI = CachedFunctionInfo[Caller];
256 // If we haven't calculated this information yet, do so now.
257 if (CallerFI.Metrics.NumBlocks == 0)
258 CallerFI.analyzeFunction(Caller);
260 // Don't inline a callee with dynamic alloca into a caller without them.
261 // Functions containing dynamic alloca's are inefficient in various ways;
262 // don't create more inefficiency.
263 if (!CallerFI.Metrics.usesDynamicAlloca)
264 return InlineCost::getNever();
267 // Add to the inline quality for properties that make the call valuable to
268 // inline. This includes factors that indicate that the result of inlining
269 // the function will be optimizable. Currently this just looks at arguments
270 // passed into the function.
273 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
274 I != E; ++I, ++ArgNo) {
275 // Each argument passed in has a cost at both the caller and the callee
276 // sides. This favors functions that take many arguments over functions
277 // that take few arguments.
280 // If this is a function being passed in, it is very likely that we will be
281 // able to turn an indirect function call into a direct function call.
282 if (isa<Function>(I))
285 // If an alloca is passed in, inlining this function is likely to allow
286 // significant future optimization possibilities (like scalar promotion, and
287 // scalarization), so encourage the inlining of the function.
289 else if (isa<AllocaInst>(I)) {
290 if (ArgNo < CalleeFI.ArgumentWeights.size())
291 InlineCost -= CalleeFI.ArgumentWeights[ArgNo].AllocaWeight;
293 // If this is a constant being passed into the function, use the argument
294 // weights calculated for the callee to determine how much will be folded
295 // away with this information.
296 } else if (isa<Constant>(I)) {
297 if (ArgNo < CalleeFI.ArgumentWeights.size())
298 InlineCost -= CalleeFI.ArgumentWeights[ArgNo].ConstantWeight;
302 // Now that we have considered all of the factors that make the call site more
303 // likely to be inlined, look at factors that make us not want to inline it.
305 // Don't inline into something too big, which would make it bigger.
306 // "size" here is the number of basic blocks, not instructions.
308 InlineCost += Caller->size()/15;
310 // Look at the size of the callee. Each instruction counts as 5.
311 InlineCost += CalleeFI.Metrics.NumInsts*5;
313 return llvm::InlineCost::get(InlineCost);
316 // getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a
317 // higher threshold to determine if the function call should be inlined.
318 float InlineCostAnalyzer::getInlineFudgeFactor(CallSite CS) {
319 Function *Callee = CS.getCalledFunction();
321 // Get information about the callee...
322 FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
324 // If we haven't calculated this information yet, do so now.
325 if (CalleeFI.Metrics.NumBlocks == 0)
326 CalleeFI.analyzeFunction(Callee);
329 // Single BB functions are often written to be inlined.
330 if (CalleeFI.Metrics.NumBlocks == 1)
333 // Be more aggressive if the function contains a good chunk (if it mades up
334 // at least 10% of the instructions) of vector instructions.
335 if (CalleeFI.Metrics.NumVectorInsts > CalleeFI.Metrics.NumInsts/2)
337 else if (CalleeFI.Metrics.NumVectorInsts > CalleeFI.Metrics.NumInsts/10)