1 //===- AlwaysInliner.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/OptimizationRemarkEmitter.h"
20 #include "llvm/Analysis/ProfileSummaryInfo.h"
21 #include "llvm/IR/Module.h"
22 #include "llvm/InitializePasses.h"
23 #include "llvm/Transforms/IPO/Inliner.h"
24 #include "llvm/Transforms/Utils/Cloning.h"
25 #include "llvm/Transforms/Utils/ModuleUtils.h"
26
27 using namespace llvm;
28
29 #define DEBUG_TYPE "inline"
30
run(Module & M,ModuleAnalysisManager & MAM)31 PreservedAnalyses AlwaysInlinerPass::run(Module &M,
32 ModuleAnalysisManager &MAM) {
33 // Add inline assumptions during code generation.
34 FunctionAnalysisManager &FAM =
35 MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
36 auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
37 return FAM.getResult<AssumptionAnalysis>(F);
38 };
39 auto &PSI = MAM.getResult<ProfileSummaryAnalysis>(M);
40
41 SmallSetVector<CallBase *, 16> Calls;
42 bool Changed = false;
43 SmallVector<Function *, 16> InlinedFunctions;
44 for (Function &F : M) {
45 // When callee coroutine function is inlined into caller coroutine function
46 // before coro-split pass,
47 // coro-early pass can not handle this quiet well.
48 // So we won't inline the coroutine function if it have not been unsplited
49 if (F.isPresplitCoroutine())
50 continue;
51
52 if (!F.isDeclaration() && isInlineViable(F).isSuccess()) {
53 Calls.clear();
54
55 for (User *U : F.users())
56 if (auto *CB = dyn_cast<CallBase>(U))
57 if (CB->getCalledFunction() == &F &&
58 CB->hasFnAttr(Attribute::AlwaysInline) &&
59 !CB->getAttributes().hasFnAttr(Attribute::NoInline))
60 Calls.insert(CB);
61
62 for (CallBase *CB : Calls) {
63 Function *Caller = CB->getCaller();
64 OptimizationRemarkEmitter ORE(Caller);
65 DebugLoc DLoc = CB->getDebugLoc();
66 BasicBlock *Block = CB->getParent();
67
68 InlineFunctionInfo IFI(
69 /*cg=*/nullptr, GetAssumptionCache, &PSI,
70 &FAM.getResult<BlockFrequencyAnalysis>(*Caller),
71 &FAM.getResult<BlockFrequencyAnalysis>(F));
72
73 InlineResult Res =
74 InlineFunction(*CB, IFI, /*MergeAttributes=*/true,
75 &FAM.getResult<AAManager>(F), InsertLifetime);
76 if (!Res.isSuccess()) {
77 ORE.emit([&]() {
78 return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc,
79 Block)
80 << "'" << ore::NV("Callee", &F) << "' is not inlined into '"
81 << ore::NV("Caller", Caller)
82 << "': " << ore::NV("Reason", Res.getFailureReason());
83 });
84 continue;
85 }
86
87 emitInlinedIntoBasedOnCost(
88 ORE, DLoc, Block, F, *Caller,
89 InlineCost::getAlways("always inline attribute"),
90 /*ForProfileContext=*/false, DEBUG_TYPE);
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:
AlwaysInlinerLegacyPass()142 AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
143 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
144 }
145
AlwaysInlinerLegacyPass(bool InsertLifetime)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().
runOnSCC(CallGraphSCC & SCC)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;
doFinalization(CallGraph & CG)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)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)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.
getInlineCost(CallBase & CB)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 if (Callee->hasFnAttribute(Attribute::AlwaysInline) && CB.isNoInline())
214 return InlineCost::getNever("noinline call site attribute");
215
216 auto IsViable = isInlineViable(*Callee);
217 if (!IsViable.isSuccess())
218 return InlineCost::getNever(IsViable.getFailureReason());
219
220 return InlineCost::getAlways("always inliner");
221 }
222