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//===- InlineCost.h - Cost analysis for inliner -----------------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file implements heuristics for inlining decisions.
#include "llvm/Analysis/CallGraphSCCPass.h"
#include <cassert>
#include <climits>
namespace llvm {
class CallSite;
class DataLayout;
class Function;
class TargetTransformInfo;
namespace InlineConstants {
// Various magic constants used to adjust heuristics.
const int InstrCost = 5;
const int IndirectCallThreshold = 100;
const int CallPenalty = 25;
const int LastCallToStaticBonus = -15000;
const int ColdccPenalty = 2000;
const int NoreturnPenalty = 10000;
/// Do not inline functions which allocate this many bytes on the stack
/// when the caller is recursive.
const unsigned TotalAllocaSizeRecursiveCaller = 1024;
/// \brief Represents the cost of inlining a function.
/// This supports special values for functions which should "always" or
/// "never" be inlined. Otherwise, the cost represents a unitless amount;
/// smaller values increase the likelihood of the function being inlined.
/// Objects of this type also provide the adjusted threshold for inlining
/// based on the information available for a particular callsite. They can be
/// directly tested to determine if inlining should occur given the cost and
/// threshold for this cost metric.
class InlineCost {
enum SentinelValues {
AlwaysInlineCost = INT_MIN,
NeverInlineCost = INT_MAX
/// \brief The estimated cost of inlining this callsite.
const int Cost;
/// \brief The adjusted threshold against which this cost was computed.
const int Threshold;
// Trivial constructor, interesting logic in the factory functions below.
InlineCost(int Cost, int Threshold) : Cost(Cost), Threshold(Threshold) {}
static InlineCost get(int Cost, int Threshold) {
assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
return InlineCost(Cost, Threshold);
static InlineCost getAlways() {
return InlineCost(AlwaysInlineCost, 0);
static InlineCost getNever() {
return InlineCost(NeverInlineCost, 0);
/// \brief Test whether the inline cost is low enough for inlining.
LLVM_EXPLICIT operator bool() const {
return Cost < Threshold;
bool isAlways() const { return Cost == AlwaysInlineCost; }
bool isNever() const { return Cost == NeverInlineCost; }
bool isVariable() const { return !isAlways() && !isNever(); }
/// \brief Get the inline cost estimate.
/// It is an error to call this on an "always" or "never" InlineCost.
int getCost() const {
assert(isVariable() && "Invalid access of InlineCost");
return Cost;
/// \brief Get the cost delta from the threshold for inlining.
/// Only valid if the cost is of the variable kind. Returns a negative
/// value if the cost is too high to inline.
int getCostDelta() const { return Threshold - getCost(); }
/// \brief Cost analyzer used by inliner.
class InlineCostAnalysis : public CallGraphSCCPass {
const TargetTransformInfo *TTI;
static char ID;
// Pass interface implementation.
void getAnalysisUsage(AnalysisUsage &AU) const override;
bool runOnSCC(CallGraphSCC &SCC) override;
/// \brief Get an InlineCost object representing the cost of inlining this
/// callsite.
/// Note that threshold is passed into this function. Only costs below the
/// threshold are computed with any accuracy. The threshold can be used to
/// bound the computation necessary to determine whether the cost is
/// sufficiently low to warrant inlining.
/// Also note that calling this function *dynamically* computes the cost of
/// inlining the callsite. It is an expensive, heavyweight call.
InlineCost getInlineCost(CallSite CS, int Threshold);
/// \brief Get an InlineCost with the callee explicitly specified.
/// This allows you to calculate the cost of inlining a function via a
/// pointer. This behaves exactly as the version with no explicit callee
/// parameter in all other respects.
// Note: This is used by out-of-tree passes, please do not remove without
// adding a replacement API.
InlineCost getInlineCost(CallSite CS, Function *Callee, int Threshold);
/// \brief Minimal filter to detect invalid constructs for inlining.
bool isInlineViable(Function &Callee);