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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 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,
     function_ref<const TargetLibraryInfo &(Function &)> GetTLI = 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,
     function_ref<const TargetLibraryInfo &(Function &)> GetTLI = 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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