Inliner.cpp revision 2ce7f303f44a09519e7f133642fb12130003057f 
1//===- Inliner.cpp - Code common to all inliners --------------------------===//
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 the mechanics required to implement inlining without
11// missing any calls and updating the call graph.  The decisions of which calls
12// are profitable to inline are implemented elsewhere.
13//
14//===----------------------------------------------------------------------===//
15
16#define DEBUG_TYPE "inline"
17#include "llvm/Module.h"
18#include "llvm/Instructions.h"
19#include "llvm/Analysis/CallGraph.h"
20#include "llvm/Support/CallSite.h"
21#include "llvm/Target/TargetData.h"
22#include "llvm/Transforms/IPO/InlinerPass.h"
23#include "llvm/Transforms/Utils/Cloning.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Support/Debug.h"
26#include "llvm/ADT/Statistic.h"
27#include <set>
28using namespace llvm;
29
30STATISTIC(NumInlined, "Number of functions inlined");
31STATISTIC(NumDeleted, "Number of functions deleted because all callers found");
32
33static cl::opt<int>
34InlineLimit("inline-threshold", cl::Hidden, cl::init(200),
35        cl::desc("Control the amount of inlining to perform (default = 200)"));
36
37Inliner::Inliner(void *ID)
38  : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {}
39
40Inliner::Inliner(void *ID, int Threshold)
41  : CallGraphSCCPass(ID), InlineThreshold(Threshold) {}
42
43/// getAnalysisUsage - For this class, we declare that we require and preserve
44/// the call graph.  If the derived class implements this method, it should
45/// always explicitly call the implementation here.
46void Inliner::getAnalysisUsage(AnalysisUsage &Info) const {
47  Info.addRequired<TargetData>();
48  CallGraphSCCPass::getAnalysisUsage(Info);
49}
50
51// InlineCallIfPossible - If it is possible to inline the specified call site,
52// do so and update the CallGraph for this operation.
53static bool InlineCallIfPossible(CallSite CS, CallGraph &CG,
54                                 const std::set<Function*> &SCCFunctions,
55                                 const TargetData &TD) {
56  Function *Callee = CS.getCalledFunction();
57  if (!InlineFunction(CS, &CG, &TD)) return false;
58
59  // If the inlined function had a higher stack protection level than the
60  // calling function, then bump up the caller's stack protection level.
61  Function *Caller = CS.getCaller();
62  if (Callee->hasFnAttr(Attribute::StackProtectReq))
63    Caller->addFnAttr(Attribute::StackProtectReq);
64  else if (Callee->hasFnAttr(Attribute::StackProtect) &&
65           !Caller->hasFnAttr(Attribute::StackProtectReq))
66    Caller->addFnAttr(Attribute::StackProtect);
67
68  // If we inlined the last possible call site to the function, delete the
69  // function body now.
70  if (Callee->use_empty() && Callee->hasInternalLinkage() &&
71      !SCCFunctions.count(Callee)) {
72    DOUT << "    -> Deleting dead function: " << Callee->getName() << "\n";
73    CallGraphNode *CalleeNode = CG[Callee];
74
75    // Remove any call graph edges from the callee to its callees.
76    CalleeNode->removeAllCalledFunctions();
77
78    // Removing the node for callee from the call graph and delete it.
79    delete CG.removeFunctionFromModule(CalleeNode);
80    ++NumDeleted;
81  }
82  return true;
83}
84
85/// shouldInline - Return true if the inliner should attempt to inline
86/// at the given CallSite.
87bool Inliner::shouldInline(CallSite CS) {
88  InlineCost IC = getInlineCost(CS);
89  float FudgeFactor = getInlineFudgeFactor(CS);
90
91  if (IC.isAlways()) {
92    DOUT << "    Inlining: cost=always"
93         << ", Call: " << *CS.getInstruction();
94    return true;
95  }
96
97  if (IC.isNever()) {
98    DOUT << "    NOT Inlining: cost=never"
99         << ", Call: " << *CS.getInstruction();
100    return false;
101  }
102
103  int Cost = IC.getValue();
104  int CurrentThreshold = InlineThreshold;
105  Function *Fn = CS.getCaller();
106  if (Fn && !Fn->isDeclaration()
107      && Fn->hasFnAttr(Attribute::OptimizeForSize)
108      && InlineThreshold != 50) {
109    CurrentThreshold = 50;
110  }
111
112  if (Cost >= (int)(CurrentThreshold * FudgeFactor)) {
113    DOUT << "    NOT Inlining: cost=" << Cost
114         << ", Call: " << *CS.getInstruction();
115    return false;
116  } else {
117    DOUT << "    Inlining: cost=" << Cost
118         << ", Call: " << *CS.getInstruction();
119    return true;
120  }
121}
122
123bool Inliner::runOnSCC(const std::vector<CallGraphNode*> &SCC) {
124  CallGraph &CG = getAnalysis<CallGraph>();
125
126  std::set<Function*> SCCFunctions;
127  DOUT << "Inliner visiting SCC:";
128  for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
129    Function *F = SCC[i]->getFunction();
130    if (F) SCCFunctions.insert(F);
131    DOUT << " " << (F ? F->getName() : "INDIRECTNODE");
132  }
133
134  // Scan through and identify all call sites ahead of time so that we only
135  // inline call sites in the original functions, not call sites that result
136  // from inlining other functions.
137  std::vector<CallSite> CallSites;
138
139  for (unsigned i = 0, e = SCC.size(); i != e; ++i)
140    if (Function *F = SCC[i]->getFunction())
141      for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
142        for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
143          CallSite CS = CallSite::get(I);
144          if (CS.getInstruction() && (!CS.getCalledFunction() ||
145                                      !CS.getCalledFunction()->isDeclaration()))
146            CallSites.push_back(CS);
147        }
148
149  DOUT << ": " << CallSites.size() << " call sites.\n";
150
151  // Now that we have all of the call sites, move the ones to functions in the
152  // current SCC to the end of the list.
153  unsigned FirstCallInSCC = CallSites.size();
154  for (unsigned i = 0; i < FirstCallInSCC; ++i)
155    if (Function *F = CallSites[i].getCalledFunction())
156      if (SCCFunctions.count(F))
157        std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
158
159  // Now that we have all of the call sites, loop over them and inline them if
160  // it looks profitable to do so.
161  bool Changed = false;
162  bool LocalChange;
163  do {
164    LocalChange = false;
165    // Iterate over the outer loop because inlining functions can cause indirect
166    // calls to become direct calls.
167    for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi)
168      if (Function *Callee = CallSites[CSi].getCalledFunction()) {
169        // Calls to external functions are never inlinable.
170        if (Callee->isDeclaration() ||
171            CallSites[CSi].getInstruction()->getParent()->getParent() ==Callee){
172          if (SCC.size() == 1) {
173            std::swap(CallSites[CSi], CallSites.back());
174            CallSites.pop_back();
175          } else {
176            // Keep the 'in SCC / not in SCC' boundary correct.
177            CallSites.erase(CallSites.begin()+CSi);
178          }
179          --CSi;
180          continue;
181        }
182
183        // If the policy determines that we should inline this function,
184        // try to do so.
185        CallSite CS = CallSites[CSi];
186        if (shouldInline(CS)) {
187          // Attempt to inline the function...
188          if (InlineCallIfPossible(CS, CG, SCCFunctions,
189                                   getAnalysis<TargetData>())) {
190            // Remove this call site from the list.  If possible, use
191            // swap/pop_back for efficiency, but do not use it if doing so would
192            // move a call site to a function in this SCC before the
193            // 'FirstCallInSCC' barrier.
194            if (SCC.size() == 1) {
195              std::swap(CallSites[CSi], CallSites.back());
196              CallSites.pop_back();
197            } else {
198              CallSites.erase(CallSites.begin()+CSi);
199            }
200            --CSi;
201
202            ++NumInlined;
203            Changed = true;
204            LocalChange = true;
205          }
206        }
207      }
208  } while (LocalChange);
209
210  return Changed;
211}
212
213// doFinalization - Remove now-dead linkonce functions at the end of
214// processing to avoid breaking the SCC traversal.
215bool Inliner::doFinalization(CallGraph &CG) {
216  return removeDeadFunctions(CG);
217}
218
219  /// removeDeadFunctions - Remove dead functions that are not included in
220  /// DNR (Do Not Remove) list.
221bool Inliner::removeDeadFunctions(CallGraph &CG,
222                                 SmallPtrSet<const Function *, 16> *DNR) {
223  std::set<CallGraphNode*> FunctionsToRemove;
224
225  // Scan for all of the functions, looking for ones that should now be removed
226  // from the program.  Insert the dead ones in the FunctionsToRemove set.
227  for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
228    CallGraphNode *CGN = I->second;
229    if (Function *F = CGN ? CGN->getFunction() : 0) {
230      // If the only remaining users of the function are dead constants, remove
231      // them.
232      F->removeDeadConstantUsers();
233
234      if (DNR && DNR->count(F))
235        continue;
236
237      if ((F->hasLinkOnceLinkage() || F->hasInternalLinkage()) &&
238          F->use_empty()) {
239
240        // Remove any call graph edges from the function to its callees.
241        CGN->removeAllCalledFunctions();
242
243        // Remove any edges from the external node to the function's call graph
244        // node.  These edges might have been made irrelegant due to
245        // optimization of the program.
246        CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
247
248        // Removing the node for callee from the call graph and delete it.
249        FunctionsToRemove.insert(CGN);
250      }
251    }
252  }
253
254  // Now that we know which functions to delete, do so.  We didn't want to do
255  // this inline, because that would invalidate our CallGraph::iterator
256  // objects. :(
257  bool Changed = false;
258  for (std::set<CallGraphNode*>::iterator I = FunctionsToRemove.begin(),
259         E = FunctionsToRemove.end(); I != E; ++I) {
260    delete CG.removeFunctionFromModule(*I);
261    ++NumDeleted;
262    Changed = true;
263  }
264
265  return Changed;
266}
267