InlineAlways.cpp revision 303975 
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.h"
16#include "llvm/ADT/SmallPtrSet.h"
17#include "llvm/Analysis/AssumptionCache.h"
18#include "llvm/Analysis/CallGraph.h"
19#include "llvm/Analysis/InlineCost.h"
20#include "llvm/Analysis/TargetLibraryInfo.h"
21#include "llvm/IR/CallSite.h"
22#include "llvm/IR/CallingConv.h"
23#include "llvm/IR/DataLayout.h"
24#include "llvm/IR/Instructions.h"
25#include "llvm/IR/IntrinsicInst.h"
26#include "llvm/IR/Module.h"
27#include "llvm/IR/Type.h"
28#include "llvm/Transforms/IPO/InlinerPass.h"
29
30using namespace llvm;
31
32#define DEBUG_TYPE "inline"
33
34namespace {
35
36/// \brief Inliner pass which only handles "always inline" functions.
37class AlwaysInliner : public Inliner {
38
39public:
40  // Use extremely low threshold.
41  AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true) {
42    initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
43  }
44
45  AlwaysInliner(bool InsertLifetime)
46      : Inliner(ID, -2000000000, InsertLifetime) {
47    initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
48  }
49
50  static char ID; // Pass identification, replacement for typeid
51
52  InlineCost getInlineCost(CallSite CS) override;
53
54  using llvm::Pass::doFinalization;
55  bool doFinalization(CallGraph &CG) override {
56    return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/ true);
57  }
58};
59
60}
61
62char AlwaysInliner::ID = 0;
63INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
64                "Inliner for always_inline functions", false, false)
65INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
66INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
67INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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      CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
97    return InlineCost::getAlways();
98
99  return InlineCost::getNever();
100}
101