1 //===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements a custom inliner that handles only functions that
11 // are marked as "always inline".
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "llvm/Transforms/IPO/AlwaysInliner.h"
16 #include "llvm/ADT/SetVector.h"
17 #include "llvm/Analysis/AssumptionCache.h"
18 #include "llvm/Analysis/InlineCost.h"
19 #include "llvm/Analysis/TargetLibraryInfo.h"
20 #include "llvm/IR/CallSite.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/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
run(Module & M,ModuleAnalysisManager &)35 PreservedAnalyses AlwaysInlinerPass::run(Module &M, ModuleAnalysisManager &) {
36 InlineFunctionInfo IFI;
37 SmallSetVector<CallSite, 16> Calls;
38 bool Changed = false;
39 SmallVector<Function *, 16> InlinedFunctions;
40 for (Function &F : M)
41 if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
42 isInlineViable(F)) {
43 Calls.clear();
44
45 for (User *U : F.users())
46 if (auto CS = CallSite(U))
47 if (CS.getCalledFunction() == &F)
48 Calls.insert(CS);
49
50 for (CallSite CS : Calls)
51 // FIXME: We really shouldn't be able to fail to inline at this point!
52 // We should do something to log or check the inline failures here.
53 Changed |=
54 InlineFunction(CS, IFI, /*CalleeAAR=*/nullptr, InsertLifetime);
55
56 // Remember to try and delete this function afterward. This both avoids
57 // re-walking the rest of the module and avoids dealing with any iterator
58 // invalidation issues while deleting functions.
59 InlinedFunctions.push_back(&F);
60 }
61
62 // Remove any live functions.
63 erase_if(InlinedFunctions, [&](Function *F) {
64 F->removeDeadConstantUsers();
65 return !F->isDefTriviallyDead();
66 });
67
68 // Delete the non-comdat ones from the module and also from our vector.
69 auto NonComdatBegin = partition(
70 InlinedFunctions, [&](Function *F) { return F->hasComdat(); });
71 for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end()))
72 M.getFunctionList().erase(F);
73 InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end());
74
75 if (!InlinedFunctions.empty()) {
76 // Now we just have the comdat functions. Filter out the ones whose comdats
77 // are not actually dead.
78 filterDeadComdatFunctions(M, InlinedFunctions);
79 // The remaining functions are actually dead.
80 for (Function *F : InlinedFunctions)
81 M.getFunctionList().erase(F);
82 }
83
84 return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
85 }
86
87 namespace {
88
89 /// Inliner pass which only handles "always inline" functions.
90 ///
91 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner
92 /// base class to provide several facilities such as array alloca merging.
93 class AlwaysInlinerLegacyPass : public LegacyInlinerBase {
94
95 public:
AlwaysInlinerLegacyPass()96 AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
97 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
98 }
99
AlwaysInlinerLegacyPass(bool InsertLifetime)100 AlwaysInlinerLegacyPass(bool InsertLifetime)
101 : LegacyInlinerBase(ID, InsertLifetime) {
102 initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
103 }
104
105 /// Main run interface method. We override here to avoid calling skipSCC().
runOnSCC(CallGraphSCC & SCC)106 bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); }
107
108 static char ID; // Pass identification, replacement for typeid
109
110 InlineCost getInlineCost(CallSite CS) override;
111
112 using llvm::Pass::doFinalization;
doFinalization(CallGraph & CG)113 bool doFinalization(CallGraph &CG) override {
114 return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
115 }
116 };
117 }
118
119 char AlwaysInlinerLegacyPass::ID = 0;
120 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline",
121 "Inliner for always_inline functions", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)122 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
123 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
124 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
125 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
126 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline",
127 "Inliner for always_inline functions", false, false)
128
129 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) {
130 return new AlwaysInlinerLegacyPass(InsertLifetime);
131 }
132
133 /// Get the inline cost for the always-inliner.
134 ///
135 /// The always inliner *only* handles functions which are marked with the
136 /// attribute to force inlining. As such, it is dramatically simpler and avoids
137 /// using the powerful (but expensive) inline cost analysis. Instead it uses
138 /// a very simple and boring direct walk of the instructions looking for
139 /// impossible-to-inline constructs.
140 ///
141 /// Note, it would be possible to go to some lengths to cache the information
142 /// computed here, but as we only expect to do this for relatively few and
143 /// small functions which have the explicit attribute to force inlining, it is
144 /// likely not worth it in practice.
getInlineCost(CallSite CS)145 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallSite CS) {
146 Function *Callee = CS.getCalledFunction();
147
148 // Only inline direct calls to functions with always-inline attributes
149 // that are viable for inlining. FIXME: We shouldn't even get here for
150 // declarations.
151 if (Callee && !Callee->isDeclaration() &&
152 CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
153 return InlineCost::getAlways();
154
155 return InlineCost::getNever();
156 }
157