1 //===- InlineCoast.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 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/InlineCost.h"
16 #include "llvm/Support/CallSite.h"
17 #include "llvm/CallingConv.h"
18 #include "llvm/IntrinsicInst.h"
22 // CountCodeReductionForConstant - Figure out an approximation for how many
23 // instructions will be constant folded if the specified value is constant.
25 unsigned InlineCostAnalyzer::FunctionInfo::
26 CountCodeReductionForConstant(Value *V) {
27 unsigned Reduction = 0;
28 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
29 if (isa<BranchInst>(*UI))
30 Reduction += 40; // Eliminating a conditional branch is a big win
31 else if (SwitchInst *SI = dyn_cast<SwitchInst>(*UI))
32 // Eliminating a switch is a big win, proportional to the number of edges
34 Reduction += (SI->getNumSuccessors()-1) * 40;
35 else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
36 // Turning an indirect call into a direct call is a BIG win
37 Reduction += CI->getCalledValue() == V ? 500 : 0;
38 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
39 // Turning an indirect call into a direct call is a BIG win
40 Reduction += II->getCalledValue() == V ? 500 : 0;
42 // Figure out if this instruction will be removed due to simple constant
44 Instruction &Inst = cast<Instruction>(**UI);
45 bool AllOperandsConstant = true;
46 for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i)
47 if (!isa<Constant>(Inst.getOperand(i)) && Inst.getOperand(i) != V) {
48 AllOperandsConstant = false;
52 if (AllOperandsConstant) {
53 // We will get to remove this instruction...
56 // And any other instructions that use it which become constants
58 Reduction += CountCodeReductionForConstant(&Inst);
65 // CountCodeReductionForAlloca - Figure out an approximation of how much smaller
66 // the function will be if it is inlined into a context where an argument
69 unsigned InlineCostAnalyzer::FunctionInfo::
70 CountCodeReductionForAlloca(Value *V) {
71 if (!isa<PointerType>(V->getType())) return 0; // Not a pointer
72 unsigned Reduction = 0;
73 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
74 Instruction *I = cast<Instruction>(*UI);
75 if (isa<LoadInst>(I) || isa<StoreInst>(I))
77 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
78 // If the GEP has variable indices, we won't be able to do much with it.
79 for (Instruction::op_iterator I = GEP->op_begin()+1, E = GEP->op_end();
81 if (!isa<Constant>(*I)) return 0;
82 Reduction += CountCodeReductionForAlloca(GEP)+15;
84 // If there is some other strange instruction, we're not going to be able
85 // to do much if we inline this.
93 /// analyzeFunction - Fill in the current structure with information gleaned
94 /// from the specified function.
95 void InlineCostAnalyzer::FunctionInfo::analyzeFunction(Function *F) {
96 unsigned NumInsts = 0, NumBlocks = 0;
98 // Look at the size of the callee. Each basic block counts as 20 units, and
99 // each instruction counts as 5.
100 for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
101 for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
103 if (isa<DbgInfoIntrinsic>(II)) continue; // Debug intrinsics don't count.
105 // Noop casts, including ptr <-> int, don't count.
106 if (const CastInst *CI = dyn_cast<CastInst>(II)) {
107 if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) ||
108 isa<PtrToIntInst>(CI))
110 } else if (const GetElementPtrInst *GEPI =
111 dyn_cast<GetElementPtrInst>(II)) {
112 // If a GEP has all constant indices, it will probably be folded with
114 bool AllConstant = true;
115 for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
116 if (!isa<ConstantInt>(GEPI->getOperand(i))) {
120 if (AllConstant) continue;
129 this->NumBlocks = NumBlocks;
130 this->NumInsts = NumInsts;
132 // Check out all of the arguments to the function, figuring out how much
133 // code can be eliminated if one of the arguments is a constant.
134 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
135 ArgumentWeights.push_back(ArgInfo(CountCodeReductionForConstant(I),
136 CountCodeReductionForAlloca(I)));
141 // getInlineCost - The heuristic used to determine if we should inline the
142 // function call or not.
144 int InlineCostAnalyzer::getInlineCost(CallSite CS, SmallPtrSet<const Function *, 16> &NeverInline) {
145 Instruction *TheCall = CS.getInstruction();
146 Function *Callee = CS.getCalledFunction();
147 const Function *Caller = TheCall->getParent()->getParent();
149 // Don't inline a directly recursive call.
150 if (Caller == Callee ||
151 // Don't inline functions which can be redefined at link-time to mean
152 // something else. link-once linkage is ok though.
153 Callee->hasWeakLinkage() ||
155 // Don't inline functions marked noinline.
156 NeverInline.count(Callee))
159 // InlineCost - This value measures how good of an inline candidate this call
160 // site is to inline. A lower inline cost make is more likely for the call to
161 // be inlined. This value may go negative.
165 // If there is only one call of the function, and it has internal linkage,
166 // make it almost guaranteed to be inlined.
168 if (Callee->hasInternalLinkage() && Callee->hasOneUse())
171 // If this function uses the coldcc calling convention, prefer not to inline
173 if (Callee->getCallingConv() == CallingConv::Cold)
176 // If the instruction after the call, or if the normal destination of the
177 // invoke is an unreachable instruction, the function is noreturn. As such,
178 // there is little point in inlining this.
179 if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) {
180 if (isa<UnreachableInst>(II->getNormalDest()->begin()))
182 } else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall)))
185 // Get information about the callee...
186 FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
188 // If we haven't calculated this information yet, do so now.
189 if (CalleeFI.NumBlocks == 0)
190 CalleeFI.analyzeFunction(Callee);
192 // Add to the inline quality for properties that make the call valuable to
193 // inline. This includes factors that indicate that the result of inlining
194 // the function will be optimizable. Currently this just looks at arguments
195 // passed into the function.
198 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
199 I != E; ++I, ++ArgNo) {
200 // Each argument passed in has a cost at both the caller and the callee
201 // sides. This favors functions that take many arguments over functions
202 // that take few arguments.
205 // If this is a function being passed in, it is very likely that we will be
206 // able to turn an indirect function call into a direct function call.
207 if (isa<Function>(I))
210 // If an alloca is passed in, inlining this function is likely to allow
211 // significant future optimization possibilities (like scalar promotion, and
212 // scalarization), so encourage the inlining of the function.
214 else if (isa<AllocaInst>(I)) {
215 if (ArgNo < CalleeFI.ArgumentWeights.size())
216 InlineCost -= CalleeFI.ArgumentWeights[ArgNo].AllocaWeight;
218 // If this is a constant being passed into the function, use the argument
219 // weights calculated for the callee to determine how much will be folded
220 // away with this information.
221 } else if (isa<Constant>(I)) {
222 if (ArgNo < CalleeFI.ArgumentWeights.size())
223 InlineCost -= CalleeFI.ArgumentWeights[ArgNo].ConstantWeight;
227 // Now that we have considered all of the factors that make the call site more
228 // likely to be inlined, look at factors that make us not want to inline it.
230 // Don't inline into something too big, which would make it bigger. Here, we
231 // count each basic block as a single unit.
233 InlineCost += Caller->size()/20;
236 // Look at the size of the callee. Each basic block counts as 20 units, and
237 // each instruction counts as 5.
238 InlineCost += CalleeFI.NumInsts*5 + CalleeFI.NumBlocks*20;