src/llvm/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/CallGraphSCCPass.h"
  18 #include <cassert>
  19 #include <climits>
  20
  21 namespace llvm {
  22 class AssumptionTracker;
  23 class CallSite;
  24 class DataLayout;
  25 class Function;
  26 class TargetTransformInfo;
  27
  28 namespace InlineConstants {
  29   // Various magic constants used to adjust heuristics.
  30   const int InstrCost = 5;
  31   const int IndirectCallThreshold = 100;
  32   const int CallPenalty = 25;
  33   const int LastCallToStaticBonus = -15000;
  34   const int ColdccPenalty = 2000;
  35   const int NoreturnPenalty = 10000;
  36   /// Do not inline functions which allocate this many bytes on the stack
  37   /// when the caller is recursive.
  38   const unsigned TotalAllocaSizeRecursiveCaller = 1024;
  39 }
  40
  41 /// \brief Represents the cost of inlining a function.
  42 ///
  43 /// This supports special values for functions which should "always" or
  44 /// "never" be inlined. Otherwise, the cost represents a unitless amount;
  45 /// smaller values increase the likelihood of the function being inlined.
  46 ///
  47 /// Objects of this type also provide the adjusted threshold for inlining
  48 /// based on the information available for a particular callsite. They can be
  49 /// directly tested to determine if inlining should occur given the cost and
  50 /// threshold for this cost metric.
  51 class InlineCost {
  52   enum SentinelValues {
  53     AlwaysInlineCost = INT_MIN,
  54     NeverInlineCost = INT_MAX
  55   };
  56
  57   /// \brief The estimated cost of inlining this callsite.
  58   const int Cost;
  59
  60   /// \brief The adjusted threshold against which this cost was computed.
  61   const int Threshold;
  62
  63   // Trivial constructor, interesting logic in the factory functions below.
  64   InlineCost(int Cost, int Threshold) : Cost(Cost), Threshold(Threshold) {}
  65
  66 public:
  67   static InlineCost get(int Cost, int Threshold) {
  68     assert(Cost > AlwaysInlineCost && "Cost crosses sentinel value");
  69     assert(Cost < NeverInlineCost && "Cost crosses sentinel value");
  70     return InlineCost(Cost, Threshold);
  71   }
  72   static InlineCost getAlways() {
  73     return InlineCost(AlwaysInlineCost, 0);
  74   }
  75   static InlineCost getNever() {
  76     return InlineCost(NeverInlineCost, 0);
  77   }
  78
  79   /// \brief Test whether the inline cost is low enough for inlining.
  80   LLVM_EXPLICIT operator bool() const {
  81     return Cost < Threshold;
  82   }
  83
  84   bool isAlways() const { return Cost == AlwaysInlineCost; }
  85   bool isNever() const { return Cost == NeverInlineCost; }
  86   bool isVariable() const { return !isAlways() && !isNever(); }
  87
  88   /// \brief Get the inline cost estimate.
  89   /// It is an error to call this on an "always" or "never" InlineCost.
  90   int getCost() const {
  91     assert(isVariable() && "Invalid access of InlineCost");
  92     return Cost;
  93   }
  94
  95   /// \brief Get the cost delta from the threshold for inlining.
  96   /// Only valid if the cost is of the variable kind. Returns a negative
  97   /// value if the cost is too high to inline.
  98   int getCostDelta() const { return Threshold - getCost(); }
  99 };
 100
 101 /// \brief Cost analyzer used by inliner.
 102 class InlineCostAnalysis : public CallGraphSCCPass {
 103   const TargetTransformInfo *TTI;
 104   AssumptionTracker *AT;
 105
 106 public:
 107   static char ID;
 108
 109   InlineCostAnalysis();
 110   ~InlineCostAnalysis();
 111
 112   // Pass interface implementation.
 113   void getAnalysisUsage(AnalysisUsage &AU) const override;
 114   bool runOnSCC(CallGraphSCC &SCC) override;
 115
 116   /// \brief Get an InlineCost object representing the cost of inlining this
 117   /// callsite.
 118   ///
 119   /// Note that threshold is passed into this function. Only costs below the
 120   /// threshold are computed with any accuracy. The threshold can be used to
 121   /// bound the computation necessary to determine whether the cost is
 122   /// sufficiently low to warrant inlining.
 123   ///
 124   /// Also note that calling this function *dynamically* computes the cost of
 125   /// inlining the callsite. It is an expensive, heavyweight call.
 126   InlineCost getInlineCost(CallSite CS, int Threshold);
 127
 128   /// \brief Get an InlineCost with the callee explicitly specified.
 129   /// This allows you to calculate the cost of inlining a function via a
 130   /// pointer. This behaves exactly as the version with no explicit callee
 131   /// parameter in all other respects.
 132   //
 133   //  Note: This is used by out-of-tree passes, please do not remove without
 134   //  adding a replacement API.
 135   InlineCost getInlineCost(CallSite CS, Function *Callee, int Threshold);
 136
 137   /// \brief Minimal filter to detect invalid constructs for inlining.
 138   bool isInlineViable(Function &Callee);
 139 };
 140
 141 }
 142
 143 #endif