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/CallingConv.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/Instructions.h"
22 #include "llvm/IR/Module.h"
23 #include "llvm/IR/Type.h"
24 #include "llvm/InitializePasses.h"
25 #include "llvm/Transforms/Coroutines.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   auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
41     return FAM.getResult<AssumptionAnalysis>(F);
42   };
43   InlineFunctionInfo IFI(/*cg=*/nullptr, GetAssumptionCache);
44 
45   SmallSetVector<CallBase *, 16> Calls;
46   bool Changed = false;
47   SmallVector<Function *, 16> InlinedFunctions;
48   for (Function &F : M) {
49     // When callee coroutine function is inlined into caller coroutine function
50     // before coro-split pass,
51     // coro-early pass can not handle this quiet well.
52     // So we won't inline the coroutine function if it have not been unsplited
53     if (F.hasFnAttribute(CORO_PRESPLIT_ATTR))
54       continue;
55 
56     if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
57         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             Calls.insert(CB);
64 
65       for (CallBase *CB : Calls)
66         // FIXME: We really shouldn't be able to fail to inline at this point!
67         // We should do something to log or check the inline failures here.
68         Changed |=
69             InlineFunction(*CB, IFI, /*CalleeAAR=*/nullptr, InsertLifetime)
70                 .isSuccess();
71 
72       // Remember to try and delete this function afterward. This both avoids
73       // re-walking the rest of the module and avoids dealing with any iterator
74       // invalidation issues while deleting functions.
75       InlinedFunctions.push_back(&F);
76     }
77   }
78 
79   // Remove any live functions.
80   erase_if(InlinedFunctions, [&](Function *F) {
81     F->removeDeadConstantUsers();
82     return !F->isDefTriviallyDead();
83   });
84 
85   // Delete the non-comdat ones from the module and also from our vector.
86   auto NonComdatBegin = partition(
87       InlinedFunctions, [&](Function *F) { return F->hasComdat(); });
88   for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end()))
89     M.getFunctionList().erase(F);
90   InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end());
91 
92   if (!InlinedFunctions.empty()) {
93     // Now we just have the comdat functions. Filter out the ones whose comdats
94     // are not actually dead.
95     filterDeadComdatFunctions(M, InlinedFunctions);
96     // The remaining functions are actually dead.
97     for (Function *F : InlinedFunctions)
98       M.getFunctionList().erase(F);
99   }
100 
101   return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
102 }
103 
104 namespace {
105 
106 /// Inliner pass which only handles "always inline" functions.
107 ///
108 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner
109 /// base class to provide several facilities such as array alloca merging.
110 class AlwaysInlinerLegacyPass : public LegacyInlinerBase {
111 
112 public:
113   AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
114     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
115   }
116 
117   AlwaysInlinerLegacyPass(bool InsertLifetime)
118       : LegacyInlinerBase(ID, InsertLifetime) {
119     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
120   }
121 
122   /// Main run interface method.  We override here to avoid calling skipSCC().
123   bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); }
124 
125   static char ID; // Pass identification, replacement for typeid
126 
127   InlineCost getInlineCost(CallBase &CB) override;
128 
129   using llvm::Pass::doFinalization;
130   bool doFinalization(CallGraph &CG) override {
131     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
132   }
133 };
134 }
135 
136 char AlwaysInlinerLegacyPass::ID = 0;
137 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline",
138                       "Inliner for always_inline functions", false, false)
139 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
140 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
141 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
142 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
143 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline",
144                     "Inliner for always_inline functions", false, false)
145 
146 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) {
147   return new AlwaysInlinerLegacyPass(InsertLifetime);
148 }
149 
150 /// Get the inline cost for the always-inliner.
151 ///
152 /// The always inliner *only* handles functions which are marked with the
153 /// attribute to force inlining. As such, it is dramatically simpler and avoids
154 /// using the powerful (but expensive) inline cost analysis. Instead it uses
155 /// a very simple and boring direct walk of the instructions looking for
156 /// impossible-to-inline constructs.
157 ///
158 /// Note, it would be possible to go to some lengths to cache the information
159 /// computed here, but as we only expect to do this for relatively few and
160 /// small functions which have the explicit attribute to force inlining, it is
161 /// likely not worth it in practice.
162 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallBase &CB) {
163   Function *Callee = CB.getCalledFunction();
164 
165   // Only inline direct calls to functions with always-inline attributes
166   // that are viable for inlining.
167   if (!Callee)
168     return InlineCost::getNever("indirect call");
169 
170   // When callee coroutine function is inlined into caller coroutine function
171   // before coro-split pass,
172   // coro-early pass can not handle this quiet well.
173   // So we won't inline the coroutine function if it have not been unsplited
174   if (Callee->hasFnAttribute(CORO_PRESPLIT_ATTR))
175     return InlineCost::getNever("unsplited coroutine call");
176 
177   // FIXME: We shouldn't even get here for declarations.
178   if (Callee->isDeclaration())
179     return InlineCost::getNever("no definition");
180 
181   if (!CB.hasFnAttr(Attribute::AlwaysInline))
182     return InlineCost::getNever("no alwaysinline attribute");
183 
184   auto IsViable = isInlineViable(*Callee);
185   if (!IsViable.isSuccess())
186     return InlineCost::getNever(IsViable.getFailureReason());
187 
188   return InlineCost::getAlways("always inliner");
189 }
190