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 #define DEBUG_TYPE "inline"
16 #include "llvm/CallingConv.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Module.h"
20 #include "llvm/Type.h"
21 #include "llvm/Analysis/CallGraph.h"
22 #include "llvm/Analysis/InlineCost.h"
23 #include "llvm/Support/CallSite.h"
24 #include "llvm/Transforms/IPO.h"
25 #include "llvm/Transforms/IPO/InlinerPass.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28
29 using namespace llvm;
30
31 namespace {
32
33 // AlwaysInliner only inlines functions that are mark as "always inline".
34 class AlwaysInliner : public Inliner {
35 public:
36 // Use extremely low threshold.
AlwaysInliner()37 AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/true) {
38 initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
39 }
AlwaysInliner(bool InsertLifetime)40 AlwaysInliner(bool InsertLifetime) : Inliner(ID, -2000000000,
41 InsertLifetime) {
42 initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
43 }
44 static char ID; // Pass identification, replacement for typeid
45 virtual InlineCost getInlineCost(CallSite CS);
doFinalization(CallGraph & CG)46 virtual bool doFinalization(CallGraph &CG) {
47 return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
48 }
49 virtual bool doInitialization(CallGraph &CG);
50 };
51 }
52
53 char AlwaysInliner::ID = 0;
54 INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
55 "Inliner for always_inline functions", false, false)
INITIALIZE_AG_DEPENDENCY(CallGraph)56 INITIALIZE_AG_DEPENDENCY(CallGraph)
57 INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
58 "Inliner for always_inline functions", false, false)
59
60 Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
61
createAlwaysInlinerPass(bool InsertLifetime)62 Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
63 return new AlwaysInliner(InsertLifetime);
64 }
65
66 /// \brief Minimal filter to detect invalid constructs for inlining.
isInlineViable(Function & F)67 static bool isInlineViable(Function &F) {
68 bool ReturnsTwice = F.hasFnAttr(Attribute::ReturnsTwice);
69 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
70 // Disallow inlining of functions which contain an indirect branch.
71 if (isa<IndirectBrInst>(BI->getTerminator()))
72 return false;
73
74 for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;
75 ++II) {
76 CallSite CS(II);
77 if (!CS)
78 continue;
79
80 // Disallow recursive calls.
81 if (&F == CS.getCalledFunction())
82 return false;
83
84 // Disallow calls which expose returns-twice to a function not previously
85 // attributed as such.
86 if (!ReturnsTwice && CS.isCall() &&
87 cast<CallInst>(CS.getInstruction())->canReturnTwice())
88 return false;
89 }
90 }
91
92 return true;
93 }
94
95 /// \brief Get the inline cost for the always-inliner.
96 ///
97 /// The always inliner *only* handles functions which are marked with the
98 /// attribute to force inlining. As such, it is dramatically simpler and avoids
99 /// using the powerful (but expensive) inline cost analysis. Instead it uses
100 /// a very simple and boring direct walk of the instructions looking for
101 /// impossible-to-inline constructs.
102 ///
103 /// Note, it would be possible to go to some lengths to cache the information
104 /// computed here, but as we only expect to do this for relatively few and
105 /// small functions which have the explicit attribute to force inlining, it is
106 /// likely not worth it in practice.
getInlineCost(CallSite CS)107 InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
108 Function *Callee = CS.getCalledFunction();
109 // We assume indirect calls aren't calling an always-inline function.
110 if (!Callee) return InlineCost::getNever();
111
112 // We can't inline calls to external functions.
113 // FIXME: We shouldn't even get here.
114 if (Callee->isDeclaration()) return InlineCost::getNever();
115
116 // Return never for anything not marked as always inline.
117 if (!Callee->hasFnAttr(Attribute::AlwaysInline))
118 return InlineCost::getNever();
119
120 // Do some minimal analysis to preclude non-viable functions.
121 if (!isInlineViable(*Callee))
122 return InlineCost::getNever();
123
124 // Otherwise, force inlining.
125 return InlineCost::getAlways();
126 }
127
128 // doInitialization - Initializes the vector of functions that have not
129 // been annotated with the "always inline" attribute.
doInitialization(CallGraph & CG)130 bool AlwaysInliner::doInitialization(CallGraph &CG) {
131 return false;
132 }
133