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() && F.hasFnAttribute(Attribute::AlwaysInline) && 58 isInlineViable(F).isSuccess()) { 59 Calls.clear(); 60 61 for (User *U : F.users()) 62 if (auto *CB = dyn_cast<CallBase>(U)) 63 if (CB->getCalledFunction() == &F) 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 // Remember to try and delete this function afterward. This both avoids 96 // re-walking the rest of the module and avoids dealing with any iterator 97 // invalidation issues while deleting functions. 98 InlinedFunctions.push_back(&F); 99 } 100 } 101 102 // Remove any live functions. 103 erase_if(InlinedFunctions, [&](Function *F) { 104 F->removeDeadConstantUsers(); 105 return !F->isDefTriviallyDead(); 106 }); 107 108 // Delete the non-comdat ones from the module and also from our vector. 109 auto NonComdatBegin = partition( 110 InlinedFunctions, [&](Function *F) { return F->hasComdat(); }); 111 for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end())) { 112 M.getFunctionList().erase(F); 113 Changed = true; 114 } 115 InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end()); 116 117 if (!InlinedFunctions.empty()) { 118 // Now we just have the comdat functions. Filter out the ones whose comdats 119 // are not actually dead. 120 filterDeadComdatFunctions(M, InlinedFunctions); 121 // The remaining functions are actually dead. 122 for (Function *F : InlinedFunctions) { 123 M.getFunctionList().erase(F); 124 Changed = true; 125 } 126 } 127 128 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all(); 129 } 130 131 namespace { 132 133 /// Inliner pass which only handles "always inline" functions. 134 /// 135 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner 136 /// base class to provide several facilities such as array alloca merging. 137 class AlwaysInlinerLegacyPass : public LegacyInlinerBase { 138 139 public: 140 AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) { 141 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 142 } 143 144 AlwaysInlinerLegacyPass(bool InsertLifetime) 145 : LegacyInlinerBase(ID, InsertLifetime) { 146 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry()); 147 } 148 149 /// Main run interface method. We override here to avoid calling skipSCC(). 150 bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); } 151 152 static char ID; // Pass identification, replacement for typeid 153 154 InlineCost getInlineCost(CallBase &CB) override; 155 156 using llvm::Pass::doFinalization; 157 bool doFinalization(CallGraph &CG) override { 158 return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true); 159 } 160 }; 161 } 162 163 char AlwaysInlinerLegacyPass::ID = 0; 164 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline", 165 "Inliner for always_inline functions", false, false) 166 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 167 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass) 168 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass) 169 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 170 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline", 171 "Inliner for always_inline functions", false, false) 172 173 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) { 174 return new AlwaysInlinerLegacyPass(InsertLifetime); 175 } 176 177 /// Get the inline cost for the always-inliner. 178 /// 179 /// The always inliner *only* handles functions which are marked with the 180 /// attribute to force inlining. As such, it is dramatically simpler and avoids 181 /// using the powerful (but expensive) inline cost analysis. Instead it uses 182 /// a very simple and boring direct walk of the instructions looking for 183 /// impossible-to-inline constructs. 184 /// 185 /// Note, it would be possible to go to some lengths to cache the information 186 /// computed here, but as we only expect to do this for relatively few and 187 /// small functions which have the explicit attribute to force inlining, it is 188 /// likely not worth it in practice. 189 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallBase &CB) { 190 Function *Callee = CB.getCalledFunction(); 191 192 // Only inline direct calls to functions with always-inline attributes 193 // that are viable for inlining. 194 if (!Callee) 195 return InlineCost::getNever("indirect call"); 196 197 // When callee coroutine function is inlined into caller coroutine function 198 // before coro-split pass, 199 // coro-early pass can not handle this quiet well. 200 // So we won't inline the coroutine function if it have not been unsplited 201 if (Callee->isPresplitCoroutine()) 202 return InlineCost::getNever("unsplited coroutine call"); 203 204 // FIXME: We shouldn't even get here for declarations. 205 if (Callee->isDeclaration()) 206 return InlineCost::getNever("no definition"); 207 208 if (!CB.hasFnAttr(Attribute::AlwaysInline)) 209 return InlineCost::getNever("no alwaysinline attribute"); 210 211 auto IsViable = isInlineViable(*Callee); 212 if (!IsViable.isSuccess()) 213 return InlineCost::getNever(IsViable.getFailureReason()); 214 215 return InlineCost::getAlways("always inliner"); 216 } 217