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//===- InlineCost.h - Cost analysis for inliner -----------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements heuristics for inlining decisions.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_INLINECOST_H
#define LLVM_ANALYSIS_INLINECOST_H
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/STLFunctionalExtras.h"
#include "llvm/Analysis/InlineModelFeatureMaps.h"
#include "llvm/IR/PassManager.h"
#include <cassert>
#include <climits>
#include <optional>
namespace llvm {
class AssumptionCache;
class OptimizationRemarkEmitter;
class BlockFrequencyInfo;
class CallBase;
class DataLayout;
class Function;
class ProfileSummaryInfo;
class TargetTransformInfo;
class TargetLibraryInfo;
namespace InlineConstants {
// Various thresholds used by inline cost analysis.
/// Use when optsize (-Os) is specified.
const int OptSizeThreshold = 50;
/// Use when minsize (-Oz) is specified.
const int OptMinSizeThreshold = 5;
/// Use when -O3 is specified.
const int OptAggressiveThreshold = 250;
// Various magic constants used to adjust heuristics.
int getInstrCost();
const int IndirectCallThreshold = 100;
const int LoopPenalty = 25;
const int LastCallToStaticBonus = 15000;
const int ColdccPenalty = 2000;
/// Do not inline functions which allocate this many bytes on the stack
/// when the caller is recursive.
const unsigned TotalAllocaSizeRecursiveCaller = 1024;
/// Do not inline dynamic allocas that have been constant propagated to be
/// static allocas above this amount in bytes.
const uint64_t MaxSimplifiedDynamicAllocaToInline = 65536;
const char FunctionInlineCostMultiplierAttributeName[] =
"function-inline-cost-multiplier";
const char MaxInlineStackSizeAttributeName[] = "inline-max-stacksize";
} // namespace InlineConstants
// The cost-benefit pair computed by cost-benefit analysis.
class CostBenefitPair {
public:
CostBenefitPair(APInt Cost, APInt Benefit)
: Cost(std::move(Cost)), Benefit(std::move(Benefit)) {}
const APInt &getCost() const { return Cost; }
const APInt &getBenefit() const { return Benefit; }
private:
APInt Cost;
APInt Benefit;
};
/// 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 };
/// The estimated cost of inlining this callsite.
int Cost = 0;
/// The adjusted threshold against which this cost was computed.
int Threshold = 0;
/// The amount of StaticBonus that has been applied.
int StaticBonusApplied = 0;
/// Must be set for Always and Never instances.
const char *Reason = nullptr;
/// The cost-benefit pair computed by cost-benefit analysis.
std::optional<CostBenefitPair> CostBenefit;
// Trivial constructor, interesting logic in the factory functions below.
InlineCost(int Cost, int Threshold, int StaticBonusApplied,
const char *Reason = nullptr,
std::optional<CostBenefitPair> CostBenefit = std::nullopt)
: Cost(Cost), Threshold(Threshold),
StaticBonusApplied(StaticBonusApplied), Reason(Reason),
CostBenefit(CostBenefit) {
assert((isVariable() || Reason) &&
"Reason must be provided for Never or Always");
}
public:
static InlineCost get(int Cost, int Threshold, int StaticBonus = 0) {
assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
return InlineCost(Cost, Threshold, StaticBonus);
}
static InlineCost
getAlways(const char *Reason,
std::optional<CostBenefitPair> CostBenefit = std::nullopt) {
return InlineCost(AlwaysInlineCost, 0, 0, Reason, CostBenefit);
}
static InlineCost
getNever(const char *Reason,
std::optional<CostBenefitPair> CostBenefit = std::nullopt) {
return InlineCost(NeverInlineCost, 0, 0, Reason, CostBenefit);
}
/// Test whether the inline cost is low enough for inlining.
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(); }
/// 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;
}
/// Get the threshold against which the cost was computed
int getThreshold() const {
assert(isVariable() && "Invalid access of InlineCost");
return Threshold;
}
/// Get the amount of StaticBonus applied.
int getStaticBonusApplied() const {
assert(isVariable() && "Invalid access of InlineCost");
return StaticBonusApplied;
}
/// Get the cost-benefit pair which was computed by cost-benefit analysis
std::optional<CostBenefitPair> getCostBenefit() const { return CostBenefit; }
/// Get the reason of Always or Never.
const char *getReason() const {
assert((Reason || isVariable()) &&
"InlineCost reason must be set for Always or Never");
return Reason;
}
/// 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(); }
};
/// InlineResult is basically true or false. For false results the message
/// describes a reason.
class InlineResult {
const char *Message = nullptr;
InlineResult(const char *Message = nullptr) : Message(Message) {}
public:
static InlineResult success() { return {}; }
static InlineResult failure(const char *Reason) {
return InlineResult(Reason);
}
bool isSuccess() const { return Message == nullptr; }
const char *getFailureReason() const {
assert(!isSuccess() &&
"getFailureReason should only be called in failure cases");
return Message;
}
};
/// Thresholds to tune inline cost analysis. The inline cost analysis decides
/// the condition to apply a threshold and applies it. Otherwise,
/// DefaultThreshold is used. If a threshold is Optional, it is applied only
/// when it has a valid value. Typically, users of inline cost analysis
/// obtain an InlineParams object through one of the \c getInlineParams methods
/// and pass it to \c getInlineCost. Some specialized versions of inliner
/// (such as the pre-inliner) might have custom logic to compute \c InlineParams
/// object.
struct InlineParams {
/// The default threshold to start with for a callee.
int DefaultThreshold = -1;
/// Threshold to use for callees with inline hint.
std::optional<int> HintThreshold;
/// Threshold to use for cold callees.
std::optional<int> ColdThreshold;
/// Threshold to use when the caller is optimized for size.
std::optional<int> OptSizeThreshold;
/// Threshold to use when the caller is optimized for minsize.
std::optional<int> OptMinSizeThreshold;
/// Threshold to use when the callsite is considered hot.
std::optional<int> HotCallSiteThreshold;
/// Threshold to use when the callsite is considered hot relative to function
/// entry.
std::optional<int> LocallyHotCallSiteThreshold;
/// Threshold to use when the callsite is considered cold.
std::optional<int> ColdCallSiteThreshold;
/// Compute inline cost even when the cost has exceeded the threshold.
std::optional<bool> ComputeFullInlineCost;
/// Indicate whether we should allow inline deferral.
std::optional<bool> EnableDeferral;
/// Indicate whether we allow inlining for recursive call.
std::optional<bool> AllowRecursiveCall = false;
};
std::optional<int> getStringFnAttrAsInt(CallBase &CB, StringRef AttrKind);
/// Generate the parameters to tune the inline cost analysis based only on the
/// commandline options.
InlineParams getInlineParams();
/// Generate the parameters to tune the inline cost analysis based on command
/// line options. If -inline-threshold option is not explicitly passed,
/// \p Threshold is used as the default threshold.
InlineParams getInlineParams(int Threshold);
/// Generate the parameters to tune the inline cost analysis based on command
/// line options. If -inline-threshold option is not explicitly passed,
/// the default threshold is computed from \p OptLevel and \p SizeOptLevel.
/// An \p OptLevel value above 3 is considered an aggressive optimization mode.
/// \p SizeOptLevel of 1 corresponds to the -Os flag and 2 corresponds to
/// the -Oz flag.
InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
/// Return the cost associated with a callsite, including parameter passing
/// and the call/return instruction.
int getCallsiteCost(const TargetTransformInfo &TTI, const CallBase &Call,
const DataLayout &DL);
/// Get an InlineCost object representing the cost of inlining this
/// callsite.
///
/// Note that a default threshold is passed into this function. This threshold
/// could be modified based on callsite's properties and only costs below this
/// new threshold are computed with any accuracy. The new 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(CallBase &Call, const InlineParams &Params,
TargetTransformInfo &CalleeTTI,
function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
function_ref<const TargetLibraryInfo &(Function &)> GetTLI,
function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
ProfileSummaryInfo *PSI = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// 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.
//
InlineCost
getInlineCost(CallBase &Call, Function *Callee, const InlineParams &Params,
TargetTransformInfo &CalleeTTI,
function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
function_ref<const TargetLibraryInfo &(Function &)> GetTLI,
function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
ProfileSummaryInfo *PSI = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Returns InlineResult::success() if the call site should be always inlined
/// because of user directives, and the inlining is viable. Returns
/// InlineResult::failure() if the inlining may never happen because of user
/// directives or incompatibilities detectable without needing callee traversal.
/// Otherwise returns std::nullopt, meaning that inlining should be decided
/// based on other criteria (e.g. cost modeling).
std::optional<InlineResult> getAttributeBasedInliningDecision(
CallBase &Call, Function *Callee, TargetTransformInfo &CalleeTTI,
function_ref<const TargetLibraryInfo &(Function &)> GetTLI);
/// Get the cost estimate ignoring thresholds. This is similar to getInlineCost
/// when passed InlineParams::ComputeFullInlineCost, or a non-null ORE. It
/// uses default InlineParams otherwise.
/// Contrary to getInlineCost, which makes a threshold-based final evaluation of
/// should/shouldn't inline, captured in InlineResult, getInliningCostEstimate
/// returns:
/// - std::nullopt, if the inlining cannot happen (is illegal)
/// - an integer, representing the cost.
std::optional<int> getInliningCostEstimate(
CallBase &Call, TargetTransformInfo &CalleeTTI,
function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
ProfileSummaryInfo *PSI = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Get the expanded cost features. The features are returned unconditionally,
/// even if inlining is impossible.
std::optional<InlineCostFeatures> getInliningCostFeatures(
CallBase &Call, TargetTransformInfo &CalleeTTI,
function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
function_ref<BlockFrequencyInfo &(Function &)> GetBFI = nullptr,
ProfileSummaryInfo *PSI = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Minimal filter to detect invalid constructs for inlining.
InlineResult isInlineViable(Function &Callee);
// This pass is used to annotate instructions during the inline process for
// debugging and analysis. The main purpose of the pass is to see and test
// inliner's decisions when creating new optimizations to InlineCost.
struct InlineCostAnnotationPrinterPass
: PassInfoMixin<InlineCostAnnotationPrinterPass> {
raw_ostream &OS;
public:
explicit InlineCostAnnotationPrinterPass(raw_ostream &OS) : OS(OS) {}
PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
static bool isRequired() { return true; }
};
} // namespace llvm
#endif
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