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 
33 using namespace llvm;
34 
35 #define DEBUG_TYPE "inline"
36 
37 PreservedAnalyses AlwaysInlinerPass::run(Module &M, ModuleAnalysisManager &) {
38   InlineFunctionInfo IFI;
39   SmallSetVector<CallSite, 16> Calls;
40   bool Changed = false;
41   for (Function &F : M)
42     if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
43         isInlineViable(F)) {
44       Calls.clear();
45 
46       for (User *U : F.users())
47         if (auto CS = CallSite(U))
48           if (CS.getCalledFunction() == &F)
49             Calls.insert(CS);
50 
51       for (CallSite CS : Calls)
52         // FIXME: We really shouldn't be able to fail to inline at this point!
53         // We should do something to log or check the inline failures here.
54         Changed |= InlineFunction(CS, IFI);
55     }
56 
57   return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
58 }
59 
60 namespace {
61 
62 /// Inliner pass which only handles "always inline" functions.
63 ///
64 /// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner
65 /// base class to provide several facilities such as array alloca merging.
66 class AlwaysInlinerLegacyPass : public LegacyInlinerBase {
67 
68 public:
69   AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
70     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
71   }
72 
73   AlwaysInlinerLegacyPass(bool InsertLifetime)
74       : LegacyInlinerBase(ID, InsertLifetime) {
75     initializeAlwaysInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
76   }
77 
78   /// Main run interface method.  We override here to avoid calling skipSCC().
79   bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); }
80 
81   static char ID; // Pass identification, replacement for typeid
82 
83   InlineCost getInlineCost(CallSite CS) override;
84 
85   using llvm::Pass::doFinalization;
86   bool doFinalization(CallGraph &CG) override {
87     return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
88   }
89 };
90 }
91 
92 char AlwaysInlinerLegacyPass::ID = 0;
93 INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline",
94                       "Inliner for always_inline functions", false, false)
95 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
96 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
97 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
98 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
99 INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline",
100                     "Inliner for always_inline functions", false, false)
101 
102 Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) {
103   return new AlwaysInlinerLegacyPass(InsertLifetime);
104 }
105 
106 /// \brief Get the inline cost for the always-inliner.
107 ///
108 /// The always inliner *only* handles functions which are marked with the
109 /// attribute to force inlining. As such, it is dramatically simpler and avoids
110 /// using the powerful (but expensive) inline cost analysis. Instead it uses
111 /// a very simple and boring direct walk of the instructions looking for
112 /// impossible-to-inline constructs.
113 ///
114 /// Note, it would be possible to go to some lengths to cache the information
115 /// computed here, but as we only expect to do this for relatively few and
116 /// small functions which have the explicit attribute to force inlining, it is
117 /// likely not worth it in practice.
118 InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallSite CS) {
119   Function *Callee = CS.getCalledFunction();
120 
121   // Only inline direct calls to functions with always-inline attributes
122   // that are viable for inlining. FIXME: We shouldn't even get here for
123   // declarations.
124   if (Callee && !Callee->isDeclaration() &&
125       CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
126     return InlineCost::getAlways();
127 
128   return InlineCost::getNever();
129 }
130