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