1 //===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
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 a custom inliner that handles only functions that
11 // are marked as "always inline".
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/Transforms/IPO.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/Analysis/AliasAnalysis.h"
18 #include "llvm/Analysis/AssumptionCache.h"
19 #include "llvm/Analysis/CallGraph.h"
20 #include "llvm/Analysis/InlineCost.h"
21 #include "llvm/IR/CallSite.h"
22 #include "llvm/IR/CallingConv.h"
23 #include "llvm/IR/DataLayout.h"
24 #include "llvm/IR/Instructions.h"
25 #include "llvm/IR/IntrinsicInst.h"
26 #include "llvm/IR/Module.h"
27 #include "llvm/IR/Type.h"
28 #include "llvm/Transforms/IPO/InlinerPass.h"
29 
30 using namespace llvm;
31 
32 #define DEBUG_TYPE "inline"
33 
34 namespace {
35 
36 /// \brief Inliner pass which only handles "always inline" functions.
37 class AlwaysInliner : public Inliner {
38   InlineCostAnalysis *ICA;
39 
40 public:
41   // Use extremely low threshold.
AlwaysInliner()42   AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true),
43                     ICA(nullptr) {
44     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
45   }
46 
AlwaysInliner(bool InsertLifetime)47   AlwaysInliner(bool InsertLifetime)
48       : Inliner(ID, -2000000000, InsertLifetime), ICA(nullptr) {
49     initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
50   }
51 
52   static char ID; // Pass identification, replacement for typeid
53 
54   InlineCost getInlineCost(CallSite CS) override;
55 
56   void getAnalysisUsage(AnalysisUsage &AU) const override;
57   bool runOnSCC(CallGraphSCC &SCC) override;
58 
59   using llvm::Pass::doFinalization;
doFinalization(CallGraph & CG)60   bool doFinalization(CallGraph &CG) override {
61     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/ true);
62   }
63 };
64 
65 }
66 
67 char AlwaysInliner::ID = 0;
68 INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
69                 "Inliner for always_inline functions", false, false)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)70 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
71 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
72 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
73 INITIALIZE_PASS_DEPENDENCY(InlineCostAnalysis)
74 INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
75                 "Inliner for always_inline functions", false, false)
76 
77 Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
78 
createAlwaysInlinerPass(bool InsertLifetime)79 Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
80   return new AlwaysInliner(InsertLifetime);
81 }
82 
83 /// \brief Get the inline cost for the always-inliner.
84 ///
85 /// The always inliner *only* handles functions which are marked with the
86 /// attribute to force inlining. As such, it is dramatically simpler and avoids
87 /// using the powerful (but expensive) inline cost analysis. Instead it uses
88 /// a very simple and boring direct walk of the instructions looking for
89 /// impossible-to-inline constructs.
90 ///
91 /// Note, it would be possible to go to some lengths to cache the information
92 /// computed here, but as we only expect to do this for relatively few and
93 /// small functions which have the explicit attribute to force inlining, it is
94 /// likely not worth it in practice.
getInlineCost(CallSite CS)95 InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
96   Function *Callee = CS.getCalledFunction();
97 
98   // Only inline direct calls to functions with always-inline attributes
99   // that are viable for inlining. FIXME: We shouldn't even get here for
100   // declarations.
101   if (Callee && !Callee->isDeclaration() &&
102       CS.hasFnAttr(Attribute::AlwaysInline) &&
103       ICA->isInlineViable(*Callee))
104     return InlineCost::getAlways();
105 
106   return InlineCost::getNever();
107 }
108 
runOnSCC(CallGraphSCC & SCC)109 bool AlwaysInliner::runOnSCC(CallGraphSCC &SCC) {
110   ICA = &getAnalysis<InlineCostAnalysis>();
111   return Inliner::runOnSCC(SCC);
112 }
113 
getAnalysisUsage(AnalysisUsage & AU) const114 void AlwaysInliner::getAnalysisUsage(AnalysisUsage &AU) const {
115   AU.addRequired<InlineCostAnalysis>();
116   Inliner::getAnalysisUsage(AU);
117 }
118