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 AssumptionCacheTracker;
23 class CallSite;
24 class DataLayout;
25 class Function;
26 class TargetTransformInfoWrapperPass;
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.
InlineCost(int Cost,int Threshold)64   InlineCost(int Cost, int Threshold) : Cost(Cost), Threshold(Threshold) {}
65 
66 public:
get(int Cost,int Threshold)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   }
getAlways()72   static InlineCost getAlways() {
73     return InlineCost(AlwaysInlineCost, 0);
74   }
getNever()75   static InlineCost getNever() {
76     return InlineCost(NeverInlineCost, 0);
77   }
78 
79   /// \brief Test whether the inline cost is low enough for inlining.
80   explicit operator bool() const {
81     return Cost < Threshold;
82   }
83 
isAlways()84   bool isAlways() const { return Cost == AlwaysInlineCost; }
isNever()85   bool isNever() const { return Cost == NeverInlineCost; }
isVariable()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.
getCost()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.
getCostDelta()98   int getCostDelta() const { return Threshold - getCost(); }
99 };
100 
101 /// \brief Cost analyzer used by inliner.
102 class InlineCostAnalysis : public CallGraphSCCPass {
103   TargetTransformInfoWrapperPass *TTIWP;
104   AssumptionCacheTracker *ACT;
105 
106 public:
107   static char ID;
108 
109   InlineCostAnalysis();
110   ~InlineCostAnalysis() override;
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
144