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      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/CodeMetrics.h"
     18 #include "llvm/Analysis/CallGraphSCCPass.h"
     19 #include <cassert>
     20 #include <climits>
     21 
     22 namespace llvm {
     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   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 DataLayout *TD;
    104   const TargetTransformInfo *TTI;
    105 
    106 public:
    107   static char ID;
    108 
    109   InlineCostAnalysis();
    110   ~InlineCostAnalysis();
    111 
    112   // Pass interface implementation.
    113   void getAnalysisUsage(AnalysisUsage &AU) const;
    114   bool runOnSCC(CallGraphSCC &SCC);
    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
    144