include/llvm/Analysis/InlineCost.h

   1 //===- InlineCost.h - Cost analysis for inliner -----------------*- C++ -*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements heuristics for inlining decisions.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_ANALYSIS_INLINECOST_H
  15 #define LLVM_ANALYSIS_INLINECOST_H
  16
  17 #include "llvm/Analysis/AssumptionCache.h"
  18 #include "llvm/Analysis/CallGraphSCCPass.h"
  19 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
  20 #include <cassert>
  21 #include <climits>
  22
  23 namespace llvm {
  24 class AssumptionCacheTracker;
  25 class BlockFrequencyInfo;
  26 class CallSite;
  27 class DataLayout;
  28 class Function;
  29 class ProfileSummaryInfo;
  30 class TargetTransformInfo;
  31
  32 namespace InlineConstants {
  33 // Various thresholds used by inline cost analysis.
  34 /// Use when optsize (-Os) is specified.
  35 const int OptSizeThreshold = 50;
  36
  37 /// Use when minsize (-Oz) is specified.
  38 const int OptMinSizeThreshold = 5;
  39
  40 /// Use when -O3 is specified.
  41 const int OptAggressiveThreshold = 250;
  42
  43 // Various magic constants used to adjust heuristics.
  44 const int InstrCost = 5;
  45 const int IndirectCallThreshold = 100;
  46 const int CallPenalty = 25;
  47 const int LastCallToStaticBonus = 15000;
  48 const int ColdccPenalty = 2000;
  49 const int NoreturnPenalty = 10000;
  50 /// Do not inline functions which allocate this many bytes on the stack
  51 /// when the caller is recursive.
  52 const unsigned TotalAllocaSizeRecursiveCaller = 1024;
  53 }
  54
  55 /// Represents the cost of inlining a function.
  56 ///
  57 /// This supports special values for functions which should "always" or
  58 /// "never" be inlined. Otherwise, the cost represents a unitless amount;
  59 /// smaller values increase the likelihood of the function being inlined.
  60 ///
  61 /// Objects of this type also provide the adjusted threshold for inlining
  62 /// based on the information available for a particular callsite. They can be
  63 /// directly tested to determine if inlining should occur given the cost and
  64 /// threshold for this cost metric.
  65 class InlineCost {
  66   enum SentinelValues {
  67     AlwaysInlineCost = INT_MIN,
  68     NeverInlineCost = INT_MAX
  69   };
  70
  71   /// The estimated cost of inlining this callsite.
  72   const int Cost;
  73
  74   /// The adjusted threshold against which this cost was computed.
  75   const int Threshold;
  76
  77   /// Must be set for Always and Never instances.
  78   const char *Reason = nullptr;
  79
  80   // Trivial constructor, interesting logic in the factory functions below.
  81   InlineCost(int Cost, int Threshold, const char *Reason = nullptr)
  82       : Cost(Cost), Threshold(Threshold), Reason(Reason) {
  83     assert((isVariable() || Reason) &&
  84            "Reason must be provided for Never or Always");
  85   }
  86
  87 public:
  88   static InlineCost get(int Cost, int Threshold) {
  89     assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
  90     assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
  91     return InlineCost(Cost, Threshold);
  92   }
  93   static InlineCost getAlways(const char *Reason) {
  94     return InlineCost(AlwaysInlineCost, 0, Reason);
  95   }
  96   static InlineCost getNever(const char *Reason) {
  97     return InlineCost(NeverInlineCost, 0, Reason);
  98   }
  99
 100   /// Test whether the inline cost is low enough for inlining.
 101   explicit operator bool() const {
 102     return Cost < Threshold;
 103   }
 104
 105   bool isAlways() const { return Cost == AlwaysInlineCost; }
 106   bool isNever() const { return Cost == NeverInlineCost; }
 107   bool isVariable() const { return !isAlways() && !isNever(); }
 108
 109   /// Get the inline cost estimate.
 110   /// It is an error to call this on an "always" or "never" InlineCost.
 111   int getCost() const {
 112     assert(isVariable() && "Invalid access of InlineCost");
 113     return Cost;
 114   }
 115
 116   /// Get the threshold against which the cost was computed
 117   int getThreshold() const {
 118     assert(isVariable() && "Invalid access of InlineCost");
 119     return Threshold;
 120   }
 121
 122   /// Get the reason of Always or Never.
 123   const char *getReason() const {
 124     assert((Reason || isVariable()) &&
 125            "InlineCost reason must be set for Always or Never");
 126     return Reason;
 127   }
 128
 129   /// Get the cost delta from the threshold for inlining.
 130   /// Only valid if the cost is of the variable kind. Returns a negative
 131   /// value if the cost is too high to inline.
 132   int getCostDelta() const { return Threshold - getCost(); }
 133 };
 134
 135 /// InlineResult is basically true or false. For false results the message
 136 /// describes a reason why it is decided not to inline.
 137 struct InlineResult {
 138   const char *message = nullptr;
 139   InlineResult(bool result, const char *message = nullptr)
 140       : message(result ? nullptr : (message ? message : "cost > threshold")) {}
 141   InlineResult(const char *message = nullptr) : message(message) {}
 142   operator bool() const { return !message; }
 143   operator const char *() const { return message; }
 144 };
 145
 146 /// Thresholds to tune inline cost analysis. The inline cost analysis decides
 147 /// the condition to apply a threshold and applies it. Otherwise,
 148 /// DefaultThreshold is used. If a threshold is Optional, it is applied only
 149 /// when it has a valid value. Typically, users of inline cost analysis
 150 /// obtain an InlineParams object through one of the \c getInlineParams methods
 151 /// and pass it to \c getInlineCost. Some specialized versions of inliner
 152 /// (such as the pre-inliner) might have custom logic to compute \c InlineParams
 153 /// object.
 154
 155 struct InlineParams {
 156   /// The default threshold to start with for a callee.
 157   int DefaultThreshold;
 158
 159   /// Threshold to use for callees with inline hint.
 160   Optional<int> HintThreshold;
 161
 162   /// Threshold to use for cold callees.
 163   Optional<int> ColdThreshold;
 164
 165   /// Threshold to use when the caller is optimized for size.
 166   Optional<int> OptSizeThreshold;
 167
 168   /// Threshold to use when the caller is optimized for minsize.
 169   Optional<int> OptMinSizeThreshold;
 170
 171   /// Threshold to use when the callsite is considered hot.
 172   Optional<int> HotCallSiteThreshold;
 173
 174   /// Threshold to use when the callsite is considered hot relative to function
 175   /// entry.
 176   Optional<int> LocallyHotCallSiteThreshold;
 177
 178   /// Threshold to use when the callsite is considered cold.
 179   Optional<int> ColdCallSiteThreshold;
 180
 181   /// Compute inline cost even when the cost has exceeded the threshold.
 182   Optional<bool> ComputeFullInlineCost;
 183 };
 184
 185 /// Generate the parameters to tune the inline cost analysis based only on the
 186 /// commandline options.
 187 InlineParams getInlineParams();
 188
 189 /// Generate the parameters to tune the inline cost analysis based on command
 190 /// line options. If -inline-threshold option is not explicitly passed,
 191 /// \p Threshold is used as the default threshold.
 192 InlineParams getInlineParams(int Threshold);
 193
 194 /// Generate the parameters to tune the inline cost analysis based on command
 195 /// line options. If -inline-threshold option is not explicitly passed,
 196 /// the default threshold is computed from \p OptLevel and \p SizeOptLevel.
 197 /// An \p OptLevel value above 3 is considered an aggressive optimization mode.
 198 /// \p SizeOptLevel of 1 corresponds to the -Os flag and 2 corresponds to
 199 /// the -Oz flag.
 200 InlineParams getInlineParams(unsigned OptLevel, unsigned SizeOptLevel);
 201
 202 /// Return the cost associated with a callsite, including parameter passing
 203 /// and the call/return instruction.
 204 int getCallsiteCost(CallSite CS, const DataLayout &DL);
 205
 206 /// Get an InlineCost object representing the cost of inlining this
 207 /// callsite.
 208 ///
 209 /// Note that a default threshold is passed into this function. This threshold
 210 /// could be modified based on callsite's properties and only costs below this
 211 /// new threshold are computed with any accuracy. The new threshold can be
 212 /// used to bound the computation necessary to determine whether the cost is
 213 /// sufficiently low to warrant inlining.
 214 ///
 215 /// Also note that calling this function *dynamically* computes the cost of
 216 /// inlining the callsite. It is an expensive, heavyweight call.
 217 InlineCost getInlineCost(
 218     CallSite CS, const InlineParams &Params, TargetTransformInfo &CalleeTTI,
 219     std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
 220     Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
 221     ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE = nullptr);
 222
 223 /// Get an InlineCost with the callee explicitly specified.
 224 /// This allows you to calculate the cost of inlining a function via a
 225 /// pointer. This behaves exactly as the version with no explicit callee
 226 /// parameter in all other respects.
 227 //
 228 InlineCost
 229 getInlineCost(CallSite CS, Function *Callee, const InlineParams &Params,
 230               TargetTransformInfo &CalleeTTI,
 231               std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
 232               Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
 233               ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE);
 234
 235 /// Minimal filter to detect invalid constructs for inlining.
 236 bool isInlineViable(Function &Callee);
 237 }
 238
 239 #endif