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/AssumptionCache.h" 18 #include "llvm/Analysis/CallGraph.h" 19 #include "llvm/Analysis/InlineCost.h" 20 #include "llvm/Analysis/TargetLibraryInfo.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. 42 AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true), 43 ICA(nullptr) { 44 initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry()); 45 } 46 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; 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) 70 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 71 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass) 72 INITIALIZE_PASS_DEPENDENCY(InlineCostAnalysis) 73 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 74 INITIALIZE_PASS_END(AlwaysInliner, "always-inline", 75 "Inliner for always_inline functions", false, false) 76 77 Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); } 78 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. 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 } 108 109 bool AlwaysInliner::runOnSCC(CallGraphSCC &SCC) { 110 ICA = &getAnalysis<InlineCostAnalysis>(); 111 return Inliner::runOnSCC(SCC); 112 } 113 114 void AlwaysInliner::getAnalysisUsage(AnalysisUsage &AU) const { 115 AU.addRequired<InlineCostAnalysis>(); 116 Inliner::getAnalysisUsage(AU); 117 } 118