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df9c75fb12
llvm-svn: 22113
276 lines
10 KiB
C++
276 lines
10 KiB
C++
//===- InlineSimple.cpp - Code to perform simple function inlining --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements bottom-up inlining of functions into callees.
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//
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//===----------------------------------------------------------------------===//
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#include "Inliner.h"
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#include "llvm/CallingConv.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Function.h"
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#include "llvm/Type.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/Transforms/IPO.h"
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using namespace llvm;
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namespace {
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struct ArgInfo {
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unsigned ConstantWeight;
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unsigned AllocaWeight;
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ArgInfo(unsigned CWeight, unsigned AWeight)
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: ConstantWeight(CWeight), AllocaWeight(AWeight) {}
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};
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// FunctionInfo - For each function, calculate the size of it in blocks and
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// instructions.
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struct FunctionInfo {
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// HasAllocas - Keep track of whether or not a function contains an alloca
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// instruction that is not in the entry block of the function. Inlining
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// this call could cause us to blow out the stack, because the stack memory
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// would never be released.
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//
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// FIXME: LLVM needs a way of dealloca'ing memory, which would make this
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// irrelevant!
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//
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bool HasAllocas;
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// NumInsts, NumBlocks - Keep track of how large each function is, which is
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// used to estimate the code size cost of inlining it.
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unsigned NumInsts, NumBlocks;
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// ArgumentWeights - Each formal argument of the function is inspected to
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// see if it is used in any contexts where making it a constant or alloca
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// would reduce the code size. If so, we add some value to the argument
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// entry here.
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std::vector<ArgInfo> ArgumentWeights;
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FunctionInfo() : HasAllocas(false), NumInsts(0), NumBlocks(0) {}
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/// analyzeFunction - Fill in the current structure with information gleaned
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/// from the specified function.
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void analyzeFunction(Function *F);
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};
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class SimpleInliner : public Inliner {
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std::map<const Function*, FunctionInfo> CachedFunctionInfo;
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public:
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int getInlineCost(CallSite CS);
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};
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RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining");
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}
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ModulePass *llvm::createFunctionInliningPass() { return new SimpleInliner(); }
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// CountCodeReductionForConstant - Figure out an approximation for how many
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// instructions will be constant folded if the specified value is constant.
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//
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static unsigned CountCodeReductionForConstant(Value *V) {
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unsigned Reduction = 0;
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for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
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if (isa<BranchInst>(*UI))
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Reduction += 40; // Eliminating a conditional branch is a big win
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else if (SwitchInst *SI = dyn_cast<SwitchInst>(*UI))
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// Eliminating a switch is a big win, proportional to the number of edges
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// deleted.
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Reduction += (SI->getNumSuccessors()-1) * 40;
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else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
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// Turning an indirect call into a direct call is a BIG win
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Reduction += CI->getCalledValue() == V ? 500 : 0;
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} else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
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// Turning an indirect call into a direct call is a BIG win
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Reduction += II->getCalledValue() == V ? 500 : 0;
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} else {
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// Figure out if this instruction will be removed due to simple constant
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// propagation.
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Instruction &Inst = cast<Instruction>(**UI);
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bool AllOperandsConstant = true;
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for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i)
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if (!isa<Constant>(Inst.getOperand(i)) && Inst.getOperand(i) != V) {
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AllOperandsConstant = false;
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break;
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}
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if (AllOperandsConstant) {
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// We will get to remove this instruction...
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Reduction += 7;
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// And any other instructions that use it which become constants
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// themselves.
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Reduction += CountCodeReductionForConstant(&Inst);
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}
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}
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return Reduction;
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}
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// CountCodeReductionForAlloca - Figure out an approximation of how much smaller
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// the function will be if it is inlined into a context where an argument
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// becomes an alloca.
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//
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static unsigned CountCodeReductionForAlloca(Value *V) {
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if (!isa<PointerType>(V->getType())) return 0; // Not a pointer
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unsigned Reduction = 0;
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for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
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Instruction *I = cast<Instruction>(*UI);
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if (isa<LoadInst>(I) || isa<StoreInst>(I))
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Reduction += 10;
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else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
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// If the GEP has variable indices, we won't be able to do much with it.
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for (Instruction::op_iterator I = GEP->op_begin()+1, E = GEP->op_end();
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I != E; ++I)
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if (!isa<Constant>(*I)) return 0;
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Reduction += CountCodeReductionForAlloca(GEP)+15;
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} else {
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// If there is some other strange instruction, we're not going to be able
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// to do much if we inline this.
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return 0;
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}
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}
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return Reduction;
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}
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/// analyzeFunction - Fill in the current structure with information gleaned
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/// from the specified function.
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void FunctionInfo::analyzeFunction(Function *F) {
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unsigned NumInsts = 0, NumBlocks = 0;
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// Look at the size of the callee. Each basic block counts as 20 units, and
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// each instruction counts as 10.
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for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
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for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
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II != E; ++II) {
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if (!isa<DbgInfoIntrinsic>(II)) ++NumInsts;
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// If there is an alloca in the body of the function, we cannot currently
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// inline the function without the risk of exploding the stack.
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if (isa<AllocaInst>(II) && BB != F->begin()) {
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HasAllocas = true;
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this->NumBlocks = this->NumInsts = 1;
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return;
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}
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}
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++NumBlocks;
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}
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this->NumBlocks = NumBlocks;
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this->NumInsts = NumInsts;
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// Check out all of the arguments to the function, figuring out how much
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// code can be eliminated if one of the arguments is a constant.
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for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
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ArgumentWeights.push_back(ArgInfo(CountCodeReductionForConstant(I),
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CountCodeReductionForAlloca(I)));
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}
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// getInlineCost - The heuristic used to determine if we should inline the
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// function call or not.
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//
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int SimpleInliner::getInlineCost(CallSite CS) {
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Instruction *TheCall = CS.getInstruction();
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Function *Callee = CS.getCalledFunction();
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const Function *Caller = TheCall->getParent()->getParent();
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// Don't inline a directly recursive call.
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if (Caller == Callee) return 2000000000;
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// InlineCost - This value measures how good of an inline candidate this call
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// site is to inline. A lower inline cost make is more likely for the call to
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// be inlined. This value may go negative.
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//
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int InlineCost = 0;
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// If there is only one call of the function, and it has internal linkage,
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// make it almost guaranteed to be inlined.
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//
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if (Callee->hasInternalLinkage() && Callee->hasOneUse())
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InlineCost -= 30000;
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// If this function uses the coldcc calling convention, prefer not to inline
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// it.
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if (Callee->getCallingConv() == CallingConv::Cold)
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InlineCost += 2000;
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// If the instruction after the call, or if the normal destination of the
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// invoke is an unreachable instruction, the function is noreturn. As such,
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// there is little point in inlining this.
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if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) {
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if (isa<UnreachableInst>(II->getNormalDest()->begin()))
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InlineCost += 10000;
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} else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall)))
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InlineCost += 10000;
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// Get information about the callee...
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FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
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// If we haven't calculated this information yet, do so now.
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if (CalleeFI.NumBlocks == 0)
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CalleeFI.analyzeFunction(Callee);
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// Don't inline calls to functions with allocas that are not in the entry
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// block of the function.
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if (CalleeFI.HasAllocas)
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return 2000000000;
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// Add to the inline quality for properties that make the call valuable to
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// inline. This includes factors that indicate that the result of inlining
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// the function will be optimizable. Currently this just looks at arguments
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// passed into the function.
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//
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unsigned ArgNo = 0;
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for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
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I != E; ++I, ++ArgNo) {
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// Each argument passed in has a cost at both the caller and the callee
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// sides. This favors functions that take many arguments over functions
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// that take few arguments.
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InlineCost -= 20;
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// If this is a function being passed in, it is very likely that we will be
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// able to turn an indirect function call into a direct function call.
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if (isa<Function>(I))
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InlineCost -= 100;
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// If an alloca is passed in, inlining this function is likely to allow
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// significant future optimization possibilities (like scalar promotion, and
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// scalarization), so encourage the inlining of the function.
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//
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else if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
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if (ArgNo < CalleeFI.ArgumentWeights.size())
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InlineCost -= CalleeFI.ArgumentWeights[ArgNo].AllocaWeight;
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// If this is a constant being passed into the function, use the argument
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// weights calculated for the callee to determine how much will be folded
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// away with this information.
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} else if (isa<Constant>(I)) {
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if (ArgNo < CalleeFI.ArgumentWeights.size())
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InlineCost -= CalleeFI.ArgumentWeights[ArgNo].ConstantWeight;
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}
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}
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// Now that we have considered all of the factors that make the call site more
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// likely to be inlined, look at factors that make us not want to inline it.
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// Don't inline into something too big, which would make it bigger. Here, we
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// count each basic block as a single unit.
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//
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InlineCost += Caller->size()/20;
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// Look at the size of the callee. Each basic block counts as 20 units, and
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// each instruction counts as 5.
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InlineCost += CalleeFI.NumInsts*5 + CalleeFI.NumBlocks*20;
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return InlineCost;
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}
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