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/AlwaysInliner.h" 16 #include "llvm/ADT/SetVector.h" 17 #include "llvm/Analysis/AssumptionCache.h" 18 #include "llvm/Analysis/InlineCost.h" 19 #include "llvm/Analysis/TargetLibraryInfo.h" 20 #include "llvm/IR/CallSite.h" 21 #include "llvm/IR/CallingConv.h" 22 #include "llvm/IR/DataLayout.h" 23 #include "llvm/IR/Instructions.h" 24 #include "llvm/IR/Module.h" 25 #include "llvm/IR/Type.h" 26 #include "llvm/Transforms/IPO.h" 27 #include "llvm/Transforms/IPO/Inliner.h" 28 #include "llvm/Transforms/Utils/Cloning.h" 29 #include "llvm/Transforms/Utils/ModuleUtils.h" 30 31 using namespace llvm; 32 33 #define DEBUG_TYPE "inline" 34 35 PreservedAnalyses AlwaysInlinerPass::run(Module &M, ModuleAnalysisManager &) { 36 InlineFunctionInfo IFI; 37 SmallSetVector<CallSite, 16> Calls; 38 bool Changed = false; 39 SmallVector<Function *, 16> InlinedFunctions; 40 for (Function &F : M) 41 if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) && 42 isInlineViable(F)) { 43 Calls.clear(); 44 45 for (User *U : F.users()) 46 if (auto CS = CallSite(U)) 47 if (CS.getCalledFunction() == &F) 48 Calls.insert(CS); 49 50 for (CallSite CS : Calls) 51 // FIXME: We really shouldn't be able to fail to inline at this point! 52 // We should do something to log or check the inline failures here. 53 Changed |= 54 InlineFunction(CS, IFI, /*CalleeAAR=*/nullptr, InsertLifetime); 55 56 // Remember to try and delete this function afterward. This both avoids 57 // re-walking the rest of the module and avoids dealing with any iterator 58 // invalidation issues while deleting functions. 59 InlinedFunctions.push_back(&F); 60 } 61 62 // Remove any live functions. 63 erase_if(InlinedFunctions, [&](Function *F) { 64 F->removeDeadConstantUsers(); 65 return !F->isDefTriviallyDead(); 66 }); 67 68 // Delete the non-comdat ones from the module and also from our vector. 69 auto NonComdatBegin = partition( 70 InlinedFunctions, [&](Function *F) { return F->hasComdat(); }); 71 for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end())) 72 M.getFunctionList().erase(F); 73 InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end()); 74 75 if (!InlinedFunctions.empty()) { 76 // Now we just have the comdat functions. Filter out the ones whose comdats 77 // are not actually dead. 78 filterDeadComdatFunctions(M, InlinedFunctions); 79 // The remaining functions are actually dead. 80 for (Function *F : InlinedFunctions) 81 M.getFunctionList().erase(F); 82 } 83 84 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all(); 85 } 86 87 namespace { 88 89 /// Inliner pass which only handles "always inline" functions. 90 /// 91 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner 92 /// base class to provide several facilities such as array alloca merging. 93 class AlwaysInlinerLegacyPass : public LegacyInlinerBase { 94 95 public: 96 AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) { 97 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 98 } 99 100 AlwaysInlinerLegacyPass(bool InsertLifetime) 101 : LegacyInlinerBase(ID, InsertLifetime) { 102 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 103 } 104 105 /// Main run interface method. We override here to avoid calling skipSCC(). 106 bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); } 107 108 static char ID; // Pass identification, replacement for typeid 109 110 InlineCost getInlineCost(CallSite CS) override; 111 112 using llvm::Pass::doFinalization; 113 bool doFinalization(CallGraph &CG) override { 114 return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true); 115 } 116 }; 117 } 118 119 char AlwaysInlinerLegacyPass::ID = 0; 120 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline", 121 "Inliner for always_inline functions", false, false) 122 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 123 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass) 124 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass) 125 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 126 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline", 127 "Inliner for always_inline functions", false, false) 128 129 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) { 130 return new AlwaysInlinerLegacyPass(InsertLifetime); 131 } 132 133 /// \brief Get the inline cost for the always-inliner. 134 /// 135 /// The always inliner *only* handles functions which are marked with the 136 /// attribute to force inlining. As such, it is dramatically simpler and avoids 137 /// using the powerful (but expensive) inline cost analysis. Instead it uses 138 /// a very simple and boring direct walk of the instructions looking for 139 /// impossible-to-inline constructs. 140 /// 141 /// Note, it would be possible to go to some lengths to cache the information 142 /// computed here, but as we only expect to do this for relatively few and 143 /// small functions which have the explicit attribute to force inlining, it is 144 /// likely not worth it in practice. 145 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallSite CS) { 146 Function *Callee = CS.getCalledFunction(); 147 148 // Only inline direct calls to functions with always-inline attributes 149 // that are viable for inlining. FIXME: We shouldn't even get here for 150 // declarations. 151 if (Callee && !Callee->isDeclaration() && 152 CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee)) 153 return InlineCost::getAlways(); 154 155 return InlineCost::getNever(); 156 } 157