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/CallGraph.h"
19 #include "llvm/Analysis/InlineCost.h"
20 #include "llvm/Analysis/ProfileSummaryInfo.h"
21 #include "llvm/Analysis/TargetLibraryInfo.h"
22 #include "llvm/IR/CallSite.h"
23 #include "llvm/IR/CallingConv.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/Instructions.h"
26 #include "llvm/IR/IntrinsicInst.h"
27 #include "llvm/IR/Module.h"
28 #include "llvm/IR/Type.h"
29 #include "llvm/Transforms/IPO.h"
30 #include "llvm/Transforms/IPO/Inliner.h"
31 #include "llvm/Transforms/Utils/Cloning.h"
32 #include "llvm/Transforms/Utils/ModuleUtils.h"
33 
34 using namespace llvm;
35 
36 #define DEBUG_TYPE "inline"
37 
38 PreservedAnalyses AlwaysInlinerPass::run(Module &M, ModuleAnalysisManager &) {
39   InlineFunctionInfo IFI;
40   SmallSetVector<CallSite, 16> Calls;
41   bool Changed = false;
42   SmallVector<Function *, 16> InlinedFunctions;
43   for (Function &F : M)
44     if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
45         isInlineViable(F)) {
46       Calls.clear();
47 
48       for (User *U : F.users())
49         if (auto CS = CallSite(U))
50           if (CS.getCalledFunction() == &F)
51             Calls.insert(CS);
52 
53       for (CallSite CS : Calls)
54         // FIXME: We really shouldn't be able to fail to inline at this point!
55         // We should do something to log or check the inline failures here.
56         Changed |= InlineFunction(CS, IFI);
57 
58       // Remember to try and delete this function afterward. This both avoids
59       // re-walking the rest of the module and avoids dealing with any iterator
60       // invalidation issues while deleting functions.
61       InlinedFunctions.push_back(&F);
62     }
63 
64   // Remove any live functions.
65   erase_if(InlinedFunctions, [&](Function *F) {
66     F->removeDeadConstantUsers();
67     return !F->isDefTriviallyDead();
68   });
69 
70   // Delete the non-comdat ones from the module and also from our vector.
71   auto NonComdatBegin = partition(
72       InlinedFunctions, [&](Function *F) { return F->hasComdat(); });
73   for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end()))
74     M.getFunctionList().erase(F);
75   InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end());
76 
77   if (!InlinedFunctions.empty()) {
78     // Now we just have the comdat functions. Filter out the ones whose comdats
79     // are not actually dead.
80     filterDeadComdatFunctions(M, InlinedFunctions);
81     // The remaining functions are actually dead.
82     for (Function *F : InlinedFunctions)
83       M.getFunctionList().erase(F);
84   }
85 
86   return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
87 }
88 
89 namespace {
90 
91 /// Inliner pass which only handles "always inline" functions.
92 ///
93 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner
94 /// base class to provide several facilities such as array alloca merging.
95 class AlwaysInlinerLegacyPass : public LegacyInlinerBase {
96 
97 public:
98   AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
99     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
100   }
101 
102   AlwaysInlinerLegacyPass(bool InsertLifetime)
103       : LegacyInlinerBase(ID, InsertLifetime) {
104     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
105   }
106 
107   /// Main run interface method.  We override here to avoid calling skipSCC().
108   bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); }
109 
110   static char ID; // Pass identification, replacement for typeid
111 
112   InlineCost getInlineCost(CallSite CS) override;
113 
114   using llvm::Pass::doFinalization;
115   bool doFinalization(CallGraph &CG) override {
116     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
117   }
118 };
119 }
120 
121 char AlwaysInlinerLegacyPass::ID = 0;
122 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline",
123                       "Inliner for always_inline functions", false, false)
124 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
125 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
126 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
127 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
128 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline",
129                     "Inliner for always_inline functions", false, false)
130 
131 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) {
132   return new AlwaysInlinerLegacyPass(InsertLifetime);
133 }
134 
135 /// \brief Get the inline cost for the always-inliner.
136 ///
137 /// The always inliner *only* handles functions which are marked with the
138 /// attribute to force inlining. As such, it is dramatically simpler and avoids
139 /// using the powerful (but expensive) inline cost analysis. Instead it uses
140 /// a very simple and boring direct walk of the instructions looking for
141 /// impossible-to-inline constructs.
142 ///
143 /// Note, it would be possible to go to some lengths to cache the information
144 /// computed here, but as we only expect to do this for relatively few and
145 /// small functions which have the explicit attribute to force inlining, it is
146 /// likely not worth it in practice.
147 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallSite CS) {
148   Function *Callee = CS.getCalledFunction();
149 
150   // Only inline direct calls to functions with always-inline attributes
151   // that are viable for inlining. FIXME: We shouldn't even get here for
152   // declarations.
153   if (Callee && !Callee->isDeclaration() &&
154       CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
155     return InlineCost::getAlways();
156 
157   return InlineCost::getNever();
158 }
159