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f7477470d3
The Caller cost info would be reset everytime a callee was inlined. If the caller has lots of calls and there is some mutual recursion going on, the caller cost info could be calculated many times. This patch reduces inliner runtime from 240s to 0.5s for a function with 20000 small function calls. This is a more conservative version of r98089 that doesn't break the clang test CodeGenCXX/temp-order.cpp. That test relies on rather extreme inlining for constant folding. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98099 91177308-0d34-0410-b5e6-96231b3b80d8
428 lines
17 KiB
C++
428 lines
17 KiB
C++
//===- InlineCost.cpp - Cost analysis for inliner -------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// 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 inline cost analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/InlineCost.h"
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#include "llvm/Support/CallSite.h"
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#include "llvm/CallingConv.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/ADT/SmallPtrSet.h"
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using namespace llvm;
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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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unsigned InlineCostAnalyzer::FunctionInfo::
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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) || isa<SwitchInst>(*UI)) {
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// We will be able to eliminate all but one of the successors.
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const TerminatorInst &TI = cast<TerminatorInst>(**UI);
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const unsigned NumSucc = TI.getNumSuccessors();
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unsigned Instrs = 0;
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for (unsigned I = 0; I != NumSucc; ++I)
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Instrs += TI.getSuccessor(I)->size();
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// We don't know which blocks will be eliminated, so use the average size.
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Reduction += InlineConstants::InstrCost*Instrs*(NumSucc-1)/NumSucc;
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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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if (CI->getCalledValue() == V)
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Reduction += InlineConstants::IndirectCallBonus;
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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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if (II->getCalledValue() == V)
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Reduction += InlineConstants::IndirectCallBonus;
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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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// We can't constant propagate instructions which have effects or
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// read memory.
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//
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// FIXME: It would be nice to capture the fact that a load from a
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// pointer-to-constant-global is actually a *really* good thing to zap.
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// Unfortunately, we don't know the pointer that may get propagated here,
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// so we can't make this decision.
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if (Inst.mayReadFromMemory() || Inst.mayHaveSideEffects() ||
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isa<AllocaInst>(Inst))
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continue;
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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 += InlineConstants::InstrCost;
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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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unsigned InlineCostAnalyzer::FunctionInfo::
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CountCodeReductionForAlloca(Value *V) {
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if (!V->getType()->isPointerTy()) 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 += InlineConstants::InstrCost;
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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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if (GEP->hasAllConstantIndices())
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Reduction += CountCodeReductionForAlloca(GEP);
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} else if (BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
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// Track pointer through bitcasts.
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Reduction += CountCodeReductionForAlloca(BCI);
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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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// callIsSmall - If a call is likely to lower to a single target instruction, or
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// is otherwise deemed small return true.
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// TODO: Perhaps calls like memcpy, strcpy, etc?
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static bool callIsSmall(const Function *F) {
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if (!F) return false;
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if (F->hasLocalLinkage()) return false;
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if (!F->hasName()) return false;
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StringRef Name = F->getName();
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// These will all likely lower to a single selection DAG node.
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if (Name == "copysign" || Name == "copysignf" ||
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Name == "fabs" || Name == "fabsf" || Name == "fabsl" ||
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Name == "sin" || Name == "sinf" || Name == "sinl" ||
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Name == "cos" || Name == "cosf" || Name == "cosl" ||
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Name == "sqrt" || Name == "sqrtf" || Name == "sqrtl" )
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return true;
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// These are all likely to be optimized into something smaller.
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if (Name == "pow" || Name == "powf" || Name == "powl" ||
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Name == "exp2" || Name == "exp2l" || Name == "exp2f" ||
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Name == "floor" || Name == "floorf" || Name == "ceil" ||
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Name == "round" || Name == "ffs" || Name == "ffsl" ||
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Name == "abs" || Name == "labs" || Name == "llabs")
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return true;
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return false;
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}
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/// analyzeBasicBlock - Fill in the current structure with information gleaned
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/// from the specified block.
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void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB) {
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++NumBlocks;
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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<PHINode>(II)) continue; // PHI nodes don't count.
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// Special handling for calls.
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if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
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if (isa<DbgInfoIntrinsic>(II))
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continue; // Debug intrinsics don't count as size.
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CallSite CS = CallSite::get(const_cast<Instruction*>(&*II));
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// If this function contains a call to setjmp or _setjmp, never inline
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// it. This is a hack because we depend on the user marking their local
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// variables as volatile if they are live across a setjmp call, and they
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// probably won't do this in callers.
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if (Function *F = CS.getCalledFunction())
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if (F->isDeclaration() &&
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(F->getName() == "setjmp" || F->getName() == "_setjmp"))
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NeverInline = true;
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if (!isa<IntrinsicInst>(II) && !callIsSmall(CS.getCalledFunction())) {
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// Each argument to a call takes on average one instruction to set up.
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NumInsts += CS.arg_size();
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++NumCalls;
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}
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}
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if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
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if (!AI->isStaticAlloca())
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this->usesDynamicAlloca = true;
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}
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if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
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++NumVectorInsts;
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if (const CastInst *CI = dyn_cast<CastInst>(II)) {
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// Noop casts, including ptr <-> int, don't count.
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if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) ||
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isa<PtrToIntInst>(CI))
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continue;
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// Result of a cmp instruction is often extended (to be used by other
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// cmp instructions, logical or return instructions). These are usually
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// nop on most sane targets.
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if (isa<CmpInst>(CI->getOperand(0)))
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continue;
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} else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(II)){
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// If a GEP has all constant indices, it will probably be folded with
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// a load/store.
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if (GEPI->hasAllConstantIndices())
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continue;
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}
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++NumInsts;
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}
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if (isa<ReturnInst>(BB->getTerminator()))
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++NumRets;
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// We never want to inline functions that contain an indirectbr. This is
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// incorrect because all the blockaddress's (in static global initializers
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// for example) would be referring to the original function, and this indirect
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// jump would jump from the inlined copy of the function into the original
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// function which is extremely undefined behavior.
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if (isa<IndirectBrInst>(BB->getTerminator()))
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NeverInline = true;
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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 CodeMetrics::analyzeFunction(Function *F) {
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// Look at the size of the callee.
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for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
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analyzeBasicBlock(&*BB);
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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 InlineCostAnalyzer::FunctionInfo::analyzeFunction(Function *F) {
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Metrics.analyzeFunction(F);
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// A function with exactly one return has it removed during the inlining
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// process (see InlineFunction), so don't count it.
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// FIXME: This knowledge should really be encoded outside of FunctionInfo.
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if (Metrics.NumRets==1)
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--Metrics.NumInsts;
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// Don't bother calculating argument weights if we are never going to inline
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// the function anyway.
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if (Metrics.NeverInline)
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return;
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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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ArgumentWeights.reserve(F->arg_size());
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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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InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS,
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SmallPtrSet<const Function *, 16> &NeverInline) {
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Instruction *TheCall = CS.getInstruction();
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Function *Callee = CS.getCalledFunction();
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Function *Caller = TheCall->getParent()->getParent();
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// Don't inline functions which can be redefined at link-time to mean
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// something else. Don't inline functions marked noinline.
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if (Callee->mayBeOverridden() ||
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Callee->hasFnAttr(Attribute::NoInline) || NeverInline.count(Callee))
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return llvm::InlineCost::getNever();
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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->hasLocalLinkage() && Callee->hasOneUse())
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InlineCost += InlineConstants::LastCallToStaticBonus;
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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 += InlineConstants::ColdccPenalty;
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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 += InlineConstants::NoreturnPenalty;
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} else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall)))
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InlineCost += InlineConstants::NoreturnPenalty;
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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.Metrics.NumBlocks == 0)
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CalleeFI.analyzeFunction(Callee);
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// If we should never inline this, return a huge cost.
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if (CalleeFI.Metrics.NeverInline)
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return InlineCost::getNever();
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// FIXME: It would be nice to kill off CalleeFI.NeverInline. Then we
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// could move this up and avoid computing the FunctionInfo for
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// things we are going to just return always inline for. This
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// requires handling setjmp somewhere else, however.
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if (!Callee->isDeclaration() && Callee->hasFnAttr(Attribute::AlwaysInline))
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return InlineCost::getAlways();
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if (CalleeFI.Metrics.usesDynamicAlloca) {
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// Get infomation about the caller...
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FunctionInfo &CallerFI = CachedFunctionInfo[Caller];
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// If we haven't calculated this information yet, do so now.
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if (CallerFI.Metrics.NumBlocks == 0)
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CallerFI.analyzeFunction(Caller);
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// Don't inline a callee with dynamic alloca into a caller without them.
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// Functions containing dynamic alloca's are inefficient in various ways;
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// don't create more inefficiency.
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if (!CallerFI.Metrics.usesDynamicAlloca)
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return InlineCost::getNever();
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}
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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. Measurements show that each argument costs about the same as an
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// instruction.
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InlineCost -= InlineConstants::InstrCost;
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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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if (isa<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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// Calls usually take a long time, so they make the inlining gain smaller.
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InlineCost += CalleeFI.Metrics.NumCalls * InlineConstants::CallPenalty;
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// Look at the size of the callee. Each instruction counts as 5.
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InlineCost += CalleeFI.Metrics.NumInsts*InlineConstants::InstrCost;
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return llvm::InlineCost::get(InlineCost);
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}
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// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a
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// higher threshold to determine if the function call should be inlined.
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float InlineCostAnalyzer::getInlineFudgeFactor(CallSite CS) {
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Function *Callee = CS.getCalledFunction();
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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.Metrics.NumBlocks == 0)
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CalleeFI.analyzeFunction(Callee);
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float Factor = 1.0f;
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// Single BB functions are often written to be inlined.
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if (CalleeFI.Metrics.NumBlocks == 1)
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Factor += 0.5f;
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// Be more aggressive if the function contains a good chunk (if it mades up
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// at least 10% of the instructions) of vector instructions.
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if (CalleeFI.Metrics.NumVectorInsts > CalleeFI.Metrics.NumInsts/2)
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Factor += 2.0f;
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else if (CalleeFI.Metrics.NumVectorInsts > CalleeFI.Metrics.NumInsts/10)
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Factor += 1.5f;
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return Factor;
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}
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/// growCachedCostInfo - update the cached cost info for Caller after Callee has
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/// been inlined.
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void
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InlineCostAnalyzer::growCachedCostInfo(Function* Caller, Function* Callee) {
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FunctionInfo &CallerFI = CachedFunctionInfo[Caller];
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// For small functions we prefer to recalculate the cost for better accuracy.
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if (CallerFI.Metrics.NumBlocks < 10 || CallerFI.Metrics.NumInsts < 1000) {
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resetCachedCostInfo(Caller);
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return;
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}
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// For large functions, we can save a lot of computation time by skipping
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// recalculations.
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if (CallerFI.Metrics.NumCalls > 0)
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--CallerFI.Metrics.NumCalls;
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if (Callee) {
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FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
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if (!CalleeFI.Metrics.NumBlocks) {
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resetCachedCostInfo(Caller);
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return;
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}
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CallerFI.Metrics.NeverInline |= CalleeFI.Metrics.NeverInline;
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CallerFI.Metrics.usesDynamicAlloca |= CalleeFI.Metrics.usesDynamicAlloca;
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CallerFI.Metrics.NumInsts += CalleeFI.Metrics.NumInsts;
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CallerFI.Metrics.NumBlocks += CalleeFI.Metrics.NumBlocks;
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CallerFI.Metrics.NumCalls += CalleeFI.Metrics.NumCalls;
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CallerFI.Metrics.NumVectorInsts += CalleeFI.Metrics.NumVectorInsts;
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CallerFI.Metrics.NumRets += CalleeFI.Metrics.NumRets;
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// analyzeBasicBlock counts each function argument as an inst.
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if (CallerFI.Metrics.NumInsts >= Callee->arg_size())
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CallerFI.Metrics.NumInsts -= Callee->arg_size();
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else
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CallerFI.Metrics.NumInsts = 0;
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}
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// We are not updating the argumentweights. We have already determined that
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// Caller is a fairly large function, so we accept the loss of precision.
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}
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