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/AliasAnalysis.h" 17 #include "llvm/Analysis/AssumptionCache.h" 18 #include "llvm/Analysis/InlineCost.h" 19 #include "llvm/Analysis/ProfileSummaryInfo.h" 20 #include "llvm/Analysis/TargetLibraryInfo.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/InitializePasses.h" 27 #include "llvm/Transforms/IPO.h" 28 #include "llvm/Transforms/IPO/Inliner.h" 29 #include "llvm/Transforms/Utils/Cloning.h" 30 #include "llvm/Transforms/Utils/ModuleUtils.h" 31 32 using namespace llvm; 33 34 #define DEBUG_TYPE "inline" 35 36 PreservedAnalyses AlwaysInlinerPass::run(Module &M, 37 ModuleAnalysisManager &MAM) { 38 // Add inline assumptions during code generation. 39 FunctionAnalysisManager &FAM = 40 MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager(); 41 auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & { 42 return FAM.getResult<AssumptionAnalysis>(F); 43 }; 44 auto &PSI = MAM.getResult<ProfileSummaryAnalysis>(M); 45 46 SmallSetVector<CallBase *, 16> Calls; 47 bool Changed = false; 48 SmallVector<Function *, 16> InlinedFunctions; 49 for (Function &F : M) { 50 // When callee coroutine function is inlined into caller coroutine function 51 // before coro-split pass, 52 // coro-early pass can not handle this quiet well. 53 // So we won't inline the coroutine function if it have not been unsplited 54 if (F.isPresplitCoroutine()) 55 continue; 56 57 if (!F.isDeclaration() && isInlineViable(F).isSuccess()) { 58 Calls.clear(); 59 60 for (User *U : F.users()) 61 if (auto *CB = dyn_cast<CallBase>(U)) 62 if (CB->getCalledFunction() == &F && 63 CB->hasFnAttr(Attribute::AlwaysInline)) 64 Calls.insert(CB); 65 66 for (CallBase *CB : Calls) { 67 Function *Caller = CB->getCaller(); 68 OptimizationRemarkEmitter ORE(Caller); 69 auto OIC = shouldInline( 70 *CB, 71 [&](CallBase &CB) { 72 return InlineCost::getAlways("always inline attribute"); 73 }, 74 ORE); 75 assert(OIC); 76 emitInlinedIntoBasedOnCost(ORE, CB->getDebugLoc(), CB->getParent(), F, 77 *Caller, *OIC, false, DEBUG_TYPE); 78 79 InlineFunctionInfo IFI( 80 /*cg=*/nullptr, GetAssumptionCache, &PSI, 81 &FAM.getResult<BlockFrequencyAnalysis>(*(CB->getCaller())), 82 &FAM.getResult<BlockFrequencyAnalysis>(F)); 83 84 InlineResult Res = InlineFunction( 85 *CB, IFI, &FAM.getResult<AAManager>(F), InsertLifetime); 86 assert(Res.isSuccess() && "unexpected failure to inline"); 87 (void)Res; 88 89 // Merge the attributes based on the inlining. 90 AttributeFuncs::mergeAttributesForInlining(*Caller, F); 91 92 Changed = true; 93 } 94 95 if (F.hasFnAttribute(Attribute::AlwaysInline)) { 96 // Remember to try and delete this function afterward. This both avoids 97 // re-walking the rest of the module and avoids dealing with any 98 // iterator invalidation issues while deleting functions. 99 InlinedFunctions.push_back(&F); 100 } 101 } 102 } 103 104 // Remove any live functions. 105 erase_if(InlinedFunctions, [&](Function *F) { 106 F->removeDeadConstantUsers(); 107 return !F->isDefTriviallyDead(); 108 }); 109 110 // Delete the non-comdat ones from the module and also from our vector. 111 auto NonComdatBegin = partition( 112 InlinedFunctions, [&](Function *F) { return F->hasComdat(); }); 113 for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end())) { 114 M.getFunctionList().erase(F); 115 Changed = true; 116 } 117 InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end()); 118 119 if (!InlinedFunctions.empty()) { 120 // Now we just have the comdat functions. Filter out the ones whose comdats 121 // are not actually dead. 122 filterDeadComdatFunctions(InlinedFunctions); 123 // The remaining functions are actually dead. 124 for (Function *F : InlinedFunctions) { 125 M.getFunctionList().erase(F); 126 Changed = true; 127 } 128 } 129 130 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all(); 131 } 132 133 namespace { 134 135 /// Inliner pass which only handles "always inline" functions. 136 /// 137 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner 138 /// base class to provide several facilities such as array alloca merging. 139 class AlwaysInlinerLegacyPass : public LegacyInlinerBase { 140 141 public: 142 AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) { 143 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 144 } 145 146 AlwaysInlinerLegacyPass(bool InsertLifetime) 147 : LegacyInlinerBase(ID, InsertLifetime) { 148 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 149 } 150 151 /// Main run interface method. We override here to avoid calling skipSCC(). 152 bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); } 153 154 static char ID; // Pass identification, replacement for typeid 155 156 InlineCost getInlineCost(CallBase &CB) override; 157 158 using llvm::Pass::doFinalization; 159 bool doFinalization(CallGraph &CG) override { 160 return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true); 161 } 162 }; 163 } 164 165 char AlwaysInlinerLegacyPass::ID = 0; 166 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline", 167 "Inliner for always_inline functions", false, false) 168 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 169 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass) 170 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass) 171 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 172 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline", 173 "Inliner for always_inline functions", false, false) 174 175 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) { 176 return new AlwaysInlinerLegacyPass(InsertLifetime); 177 } 178 179 /// Get the inline cost for the always-inliner. 180 /// 181 /// The always inliner *only* handles functions which are marked with the 182 /// attribute to force inlining. As such, it is dramatically simpler and avoids 183 /// using the powerful (but expensive) inline cost analysis. Instead it uses 184 /// a very simple and boring direct walk of the instructions looking for 185 /// impossible-to-inline constructs. 186 /// 187 /// Note, it would be possible to go to some lengths to cache the information 188 /// computed here, but as we only expect to do this for relatively few and 189 /// small functions which have the explicit attribute to force inlining, it is 190 /// likely not worth it in practice. 191 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallBase &CB) { 192 Function *Callee = CB.getCalledFunction(); 193 194 // Only inline direct calls to functions with always-inline attributes 195 // that are viable for inlining. 196 if (!Callee) 197 return InlineCost::getNever("indirect call"); 198 199 // When callee coroutine function is inlined into caller coroutine function 200 // before coro-split pass, 201 // coro-early pass can not handle this quiet well. 202 // So we won't inline the coroutine function if it have not been unsplited 203 if (Callee->isPresplitCoroutine()) 204 return InlineCost::getNever("unsplited coroutine call"); 205 206 // FIXME: We shouldn't even get here for declarations. 207 if (Callee->isDeclaration()) 208 return InlineCost::getNever("no definition"); 209 210 if (!CB.hasFnAttr(Attribute::AlwaysInline)) 211 return InlineCost::getNever("no alwaysinline attribute"); 212 213 auto IsViable = isInlineViable(*Callee); 214 if (!IsViable.isSuccess()) 215 return InlineCost::getNever(IsViable.getFailureReason()); 216 217 return InlineCost::getAlways("always inliner"); 218 } 219