InlineAlways.cpp revision 263508 
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/Transforms/IPO.h"
17#include "llvm/ADT/SmallPtrSet.h"
18#include "llvm/Analysis/CallGraph.h"
19#include "llvm/Analysis/InlineCost.h"
20#include "llvm/IR/CallingConv.h"
21#include "llvm/IR/DataLayout.h"
22#include "llvm/IR/Instructions.h"
23#include "llvm/IR/IntrinsicInst.h"
24#include "llvm/IR/Module.h"
25#include "llvm/IR/Type.h"
26#include "llvm/Support/CallSite.h"
27#include "llvm/Transforms/IPO/InlinerPass.h"
28
29using namespace llvm;
30
31namespace {
32
33/// \brief Inliner pass which only handles "always inline" functions.
34class AlwaysInliner : public Inliner {
35  InlineCostAnalysis *ICA;
36
37public:
38  // Use extremely low threshold.
39  AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true), ICA(0) {
40    initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
41  }
42
43  AlwaysInliner(bool InsertLifetime)
44      : Inliner(ID, -2000000000, InsertLifetime), ICA(0) {
45    initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
46  }
47
48  static char ID; // Pass identification, replacement for typeid
49
50  virtual InlineCost getInlineCost(CallSite CS);
51
52  virtual void getAnalysisUsage(AnalysisUsage &AU) const;
53  virtual bool runOnSCC(CallGraphSCC &SCC);
54
55  using llvm::Pass::doFinalization;
56  virtual bool doFinalization(CallGraph &CG) {
57    return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/ true);
58  }
59};
60
61}
62
63char AlwaysInliner::ID = 0;
64INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
65                "Inliner for always_inline functions", false, false)
66INITIALIZE_PASS_DEPENDENCY(CallGraph)
67INITIALIZE_PASS_DEPENDENCY(InlineCostAnalysis)
68INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
69                "Inliner for always_inline functions", false, false)
70
71Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
72
73Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
74  return new AlwaysInliner(InsertLifetime);
75}
76
77/// \brief Get the inline cost for the always-inliner.
78///
79/// The always inliner *only* handles functions which are marked with the
80/// attribute to force inlining. As such, it is dramatically simpler and avoids
81/// using the powerful (but expensive) inline cost analysis. Instead it uses
82/// a very simple and boring direct walk of the instructions looking for
83/// impossible-to-inline constructs.
84///
85/// Note, it would be possible to go to some lengths to cache the information
86/// computed here, but as we only expect to do this for relatively few and
87/// small functions which have the explicit attribute to force inlining, it is
88/// likely not worth it in practice.
89InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
90  Function *Callee = CS.getCalledFunction();
91
92  // Only inline direct calls to functions with always-inline attributes
93  // that are viable for inlining. FIXME: We shouldn't even get here for
94  // declarations.
95  if (Callee && !Callee->isDeclaration() &&
96      Callee->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
97                                           Attribute::AlwaysInline) &&
98      ICA->isInlineViable(*Callee))
99    return InlineCost::getAlways();
100
101  return InlineCost::getNever();
102}
103
104bool AlwaysInliner::runOnSCC(CallGraphSCC &SCC) {
105  ICA = &getAnalysis<InlineCostAnalysis>();
106  return Inliner::runOnSCC(SCC);
107}
108
109void AlwaysInliner::getAnalysisUsage(AnalysisUsage &AU) const {
110  AU.addRequired<InlineCostAnalysis>();
111  Inliner::getAnalysisUsage(AU);
112}
113