1 //===- InlineAlways.cpp - Code to inline always_inline functions ----------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements a custom inliner that handles only functions that 10 // are marked as "always inline". 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/Transforms/IPO/AlwaysInliner.h" 15 #include "llvm/ADT/SetVector.h" 16 #include "llvm/Analysis/AssumptionCache.h" 17 #include "llvm/Analysis/InlineCost.h" 18 #include "llvm/Analysis/TargetLibraryInfo.h" 19 #include "llvm/IR/CallSite.h" 20 #include "llvm/IR/CallingConv.h" 21 #include "llvm/IR/DataLayout.h" 22 #include "llvm/IR/Instructions.h" 23 #include "llvm/IR/Module.h" 24 #include "llvm/IR/Type.h" 25 #include "llvm/InitializePasses.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, 36 ModuleAnalysisManager &MAM) { 37 // Add inline assumptions during code generation. 38 FunctionAnalysisManager &FAM = 39 MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager(); 40 std::function<AssumptionCache &(Function &)> GetAssumptionCache = 41 [&](Function &F) -> AssumptionCache & { 42 return FAM.getResult<AssumptionAnalysis>(F); 43 }; 44 InlineFunctionInfo IFI(/*cg=*/nullptr, &GetAssumptionCache); 45 46 SmallSetVector<CallSite, 16> Calls; 47 bool Changed = false; 48 SmallVector<Function *, 16> InlinedFunctions; 49 for (Function &F : M) 50 if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) && 51 isInlineViable(F)) { 52 Calls.clear(); 53 54 for (User *U : F.users()) 55 if (auto CS = CallSite(U)) 56 if (CS.getCalledFunction() == &F) 57 Calls.insert(CS); 58 59 for (CallSite CS : Calls) 60 // FIXME: We really shouldn't be able to fail to inline at this point! 61 // We should do something to log or check the inline failures here. 62 Changed |= 63 InlineFunction(CS, IFI, /*CalleeAAR=*/nullptr, InsertLifetime); 64 65 // Remember to try and delete this function afterward. This both avoids 66 // re-walking the rest of the module and avoids dealing with any iterator 67 // invalidation issues while deleting functions. 68 InlinedFunctions.push_back(&F); 69 } 70 71 // Remove any live functions. 72 erase_if(InlinedFunctions, [&](Function *F) { 73 F->removeDeadConstantUsers(); 74 return !F->isDefTriviallyDead(); 75 }); 76 77 // Delete the non-comdat ones from the module and also from our vector. 78 auto NonComdatBegin = partition( 79 InlinedFunctions, [&](Function *F) { return F->hasComdat(); }); 80 for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end())) 81 M.getFunctionList().erase(F); 82 InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end()); 83 84 if (!InlinedFunctions.empty()) { 85 // Now we just have the comdat functions. Filter out the ones whose comdats 86 // are not actually dead. 87 filterDeadComdatFunctions(M, InlinedFunctions); 88 // The remaining functions are actually dead. 89 for (Function *F : InlinedFunctions) 90 M.getFunctionList().erase(F); 91 } 92 93 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all(); 94 } 95 96 namespace { 97 98 /// Inliner pass which only handles "always inline" functions. 99 /// 100 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner 101 /// base class to provide several facilities such as array alloca merging. 102 class AlwaysInlinerLegacyPass : public LegacyInlinerBase { 103 104 public: 105 AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) { 106 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 107 } 108 109 AlwaysInlinerLegacyPass(bool InsertLifetime) 110 : LegacyInlinerBase(ID, InsertLifetime) { 111 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 112 } 113 114 /// Main run interface method. We override here to avoid calling skipSCC(). 115 bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); } 116 117 static char ID; // Pass identification, replacement for typeid 118 119 InlineCost getInlineCost(CallSite CS) override; 120 121 using llvm::Pass::doFinalization; 122 bool doFinalization(CallGraph &CG) override { 123 return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true); 124 } 125 }; 126 } 127 128 char AlwaysInlinerLegacyPass::ID = 0; 129 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline", 130 "Inliner for always_inline functions", false, false) 131 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 132 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass) 133 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass) 134 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 135 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline", 136 "Inliner for always_inline functions", false, false) 137 138 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) { 139 return new AlwaysInlinerLegacyPass(InsertLifetime); 140 } 141 142 /// Get the inline cost for the always-inliner. 143 /// 144 /// The always inliner *only* handles functions which are marked with the 145 /// attribute to force inlining. As such, it is dramatically simpler and avoids 146 /// using the powerful (but expensive) inline cost analysis. Instead it uses 147 /// a very simple and boring direct walk of the instructions looking for 148 /// impossible-to-inline constructs. 149 /// 150 /// Note, it would be possible to go to some lengths to cache the information 151 /// computed here, but as we only expect to do this for relatively few and 152 /// small functions which have the explicit attribute to force inlining, it is 153 /// likely not worth it in practice. 154 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallSite CS) { 155 Function *Callee = CS.getCalledFunction(); 156 157 // Only inline direct calls to functions with always-inline attributes 158 // that are viable for inlining. 159 if (!Callee) 160 return InlineCost::getNever("indirect call"); 161 162 // FIXME: We shouldn't even get here for declarations. 163 if (Callee->isDeclaration()) 164 return InlineCost::getNever("no definition"); 165 166 if (!CS.hasFnAttr(Attribute::AlwaysInline)) 167 return InlineCost::getNever("no alwaysinline attribute"); 168 169 auto IsViable = isInlineViable(*Callee); 170 if (!IsViable) 171 return InlineCost::getNever(IsViable.message); 172 173 return InlineCost::getAlways("always inliner"); 174 } 175