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