Inliner.cpp revision ae56c0de911bf5328ffda48e51ce37bcd7aa0d76 
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/IntrinsicInst.h"
20#include "llvm/Analysis/CallGraph.h"
21#include "llvm/Support/CallSite.h"
22#include "llvm/Target/TargetData.h"
23#include "llvm/Transforms/IPO/InlinerPass.h"
24#include "llvm/Transforms/Utils/Cloning.h"
25#include "llvm/Support/CommandLine.h"
26#include "llvm/Support/Debug.h"
27#include "llvm/Support/raw_ostream.h"
28#include "llvm/ADT/Statistic.h"
29#include <set>
30using namespace llvm;
31
32STATISTIC(NumInlined, "Number of functions inlined");
33STATISTIC(NumDeleted, "Number of functions deleted because all callers found");
34
35static cl::opt<int>
36InlineLimit("inline-threshold", cl::Hidden, cl::init(200), cl::ZeroOrMore,
37        cl::desc("Control the amount of inlining to perform (default = 200)"));
38
39Inliner::Inliner(void *ID)
40  : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {}
41
42Inliner::Inliner(void *ID, int Threshold)
43  : CallGraphSCCPass(ID), InlineThreshold(Threshold) {}
44
45/// getAnalysisUsage - For this class, we declare that we require and preserve
46/// the call graph.  If the derived class implements this method, it should
47/// always explicitly call the implementation here.
48void Inliner::getAnalysisUsage(AnalysisUsage &Info) const {
49  CallGraphSCCPass::getAnalysisUsage(Info);
50}
51
52// InlineCallIfPossible - If it is possible to inline the specified call site,
53// do so and update the CallGraph for this operation.
54bool Inliner::InlineCallIfPossible(CallSite CS, CallGraph &CG,
55                                 const SmallPtrSet<Function*, 8> &SCCFunctions,
56                                 const TargetData *TD) {
57  Function *Callee = CS.getCalledFunction();
58  Function *Caller = CS.getCaller();
59
60  if (!InlineFunction(CS, &CG, TD)) return false;
61
62  // If the inlined function had a higher stack protection level than the
63  // calling function, then bump up the caller's stack protection level.
64  if (Callee->hasFnAttr(Attribute::StackProtectReq))
65    Caller->addFnAttr(Attribute::StackProtectReq);
66  else if (Callee->hasFnAttr(Attribute::StackProtect) &&
67           !Caller->hasFnAttr(Attribute::StackProtectReq))
68    Caller->addFnAttr(Attribute::StackProtect);
69
70  // If we inlined the last possible call site to the function, delete the
71  // function body now.
72  if (Callee->use_empty() &&
73      (Callee->hasLocalLinkage() || Callee->hasAvailableExternallyLinkage()) &&
74      !SCCFunctions.count(Callee)) {
75    DEBUG(errs() << "    -> Deleting dead function: "
76          << Callee->getName() << "\n");
77    CallGraphNode *CalleeNode = CG[Callee];
78
79    // Remove any call graph edges from the callee to its callees.
80    CalleeNode->removeAllCalledFunctions();
81
82    resetCachedCostInfo(CalleeNode->getFunction());
83
84    // Removing the node for callee from the call graph and delete it.
85    delete CG.removeFunctionFromModule(CalleeNode);
86    ++NumDeleted;
87  }
88  return true;
89}
90
91/// shouldInline - Return true if the inliner should attempt to inline
92/// at the given CallSite.
93bool Inliner::shouldInline(CallSite CS) {
94  InlineCost IC = getInlineCost(CS);
95
96  if (IC.isAlways()) {
97    DEBUG(errs() << "    Inlining: cost=always"
98          << ", Call: " << *CS.getInstruction() << "\n");
99    return true;
100  }
101
102  if (IC.isNever()) {
103    DEBUG(errs() << "    NOT Inlining: cost=never"
104          << ", Call: " << *CS.getInstruction() << "\n");
105    return false;
106  }
107
108  int Cost = IC.getValue();
109  int CurrentThreshold = InlineThreshold;
110  Function *Fn = CS.getCaller();
111  if (Fn && !Fn->isDeclaration() &&
112      Fn->hasFnAttr(Attribute::OptimizeForSize) &&
113      InlineThreshold != 50)
114    CurrentThreshold = 50;
115
116  float FudgeFactor = getInlineFudgeFactor(CS);
117  if (Cost >= (int)(CurrentThreshold * FudgeFactor)) {
118    DEBUG(errs() << "    NOT Inlining: cost=" << Cost
119          << ", Call: " << *CS.getInstruction() << "\n");
120    return false;
121  }
122
123  DEBUG(errs() << "    Inlining: cost=" << Cost
124        << ", Call: " << *CS.getInstruction() << "\n");
125  return true;
126}
127
128bool Inliner::runOnSCC(const std::vector<CallGraphNode*> &SCC) {
129  CallGraph &CG = getAnalysis<CallGraph>();
130  const TargetData *TD = getAnalysisIfAvailable<TargetData>();
131
132  SmallPtrSet<Function*, 8> SCCFunctions;
133  DEBUG(errs() << "Inliner visiting SCC:");
134  for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
135    Function *F = SCC[i]->getFunction();
136    if (F) SCCFunctions.insert(F);
137    DEBUG(errs() << " " << (F ? F->getName() : "INDIRECTNODE"));
138  }
139
140  // Scan through and identify all call sites ahead of time so that we only
141  // inline call sites in the original functions, not call sites that result
142  // from inlining other functions.
143  std::vector<CallSite> CallSites;
144
145  for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
146    Function *F = SCC[i]->getFunction();
147    if (!F) continue;
148
149    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
150      for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
151        CallSite CS = CallSite::get(I);
152        if (CS.getInstruction() == 0 || isa<DbgInfoIntrinsic>(I))
153          continue;
154
155        if (CS.getCalledFunction() == 0 ||
156            !CS.getCalledFunction()->isDeclaration())
157          CallSites.push_back(CS);
158      }
159  }
160
161  DEBUG(errs() << ": " << CallSites.size() << " call sites.\n");
162
163  // Now that we have all of the call sites, move the ones to functions in the
164  // current SCC to the end of the list.
165  unsigned FirstCallInSCC = CallSites.size();
166  for (unsigned i = 0; i < FirstCallInSCC; ++i)
167    if (Function *F = CallSites[i].getCalledFunction())
168      if (SCCFunctions.count(F))
169        std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
170
171  // Now that we have all of the call sites, loop over them and inline them if
172  // it looks profitable to do so.
173  bool Changed = false;
174  bool LocalChange;
175  do {
176    LocalChange = false;
177    // Iterate over the outer loop because inlining functions can cause indirect
178    // calls to become direct calls.
179    for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
180      // We can only inline direct calls.
181      Function *Callee = CallSites[CSi].getCalledFunction();
182      if (!Callee) continue;
183
184      // Calls to external functions are never inlinable.
185      if (Callee->isDeclaration()) {
186        if (SCC.size() == 1) {
187          std::swap(CallSites[CSi], CallSites.back());
188          CallSites.pop_back();
189        } else {
190          // Keep the 'in SCC / not in SCC' boundary correct.
191          CallSites.erase(CallSites.begin()+CSi);
192        }
193        --CSi;
194        continue;
195      }
196
197      // If the policy determines that we should inline this function,
198      // try to do so.
199      CallSite CS = CallSites[CSi];
200      if (!shouldInline(CS))
201        continue;
202
203      Function *Caller = CS.getCaller();
204      // Attempt to inline the function...
205      if (!InlineCallIfPossible(CS, CG, SCCFunctions, TD))
206        continue;
207
208      // Remove any cached cost info for this caller, as inlining the
209      // callee has increased the size of the caller (which may be the
210      // same as the callee).
211      resetCachedCostInfo(Caller);
212
213      // Remove this call site from the list.  If possible, use
214      // swap/pop_back for efficiency, but do not use it if doing so would
215      // move a call site to a function in this SCC before the
216      // 'FirstCallInSCC' barrier.
217      if (SCC.size() == 1) {
218        std::swap(CallSites[CSi], CallSites.back());
219        CallSites.pop_back();
220      } else {
221        CallSites.erase(CallSites.begin()+CSi);
222      }
223      --CSi;
224
225      ++NumInlined;
226      Changed = true;
227      LocalChange = true;
228    }
229  } while (LocalChange);
230
231  return Changed;
232}
233
234// doFinalization - Remove now-dead linkonce functions at the end of
235// processing to avoid breaking the SCC traversal.
236bool Inliner::doFinalization(CallGraph &CG) {
237  return removeDeadFunctions(CG);
238}
239
240/// removeDeadFunctions - Remove dead functions that are not included in
241/// DNR (Do Not Remove) list.
242bool Inliner::removeDeadFunctions(CallGraph &CG,
243                                  SmallPtrSet<const Function *, 16> *DNR) {
244  SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove;
245
246  // Scan for all of the functions, looking for ones that should now be removed
247  // from the program.  Insert the dead ones in the FunctionsToRemove set.
248  for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
249    CallGraphNode *CGN = I->second;
250    if (CGN == 0 || CGN->getFunction() == 0)
251      continue;
252
253    Function *F = CGN->getFunction();
254
255    // If the only remaining users of the function are dead constants, remove
256    // them.
257    F->removeDeadConstantUsers();
258
259    if (DNR && DNR->count(F))
260      continue;
261    if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage())
262      continue;
263    if (!F->use_empty())
264      continue;
265
266    // Remove any call graph edges from the function to its callees.
267    CGN->removeAllCalledFunctions();
268
269    // Remove any edges from the external node to the function's call graph
270    // node.  These edges might have been made irrelegant due to
271    // optimization of the program.
272    CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
273
274    // Removing the node for callee from the call graph and delete it.
275    FunctionsToRemove.insert(CGN);
276  }
277
278  // Now that we know which functions to delete, do so.  We didn't want to do
279  // this inline, because that would invalidate our CallGraph::iterator
280  // objects. :(
281  //
282  // Note that it doesn't matter that we are iterating over a non-stable set
283  // here to do this, it doesn't matter which order the functions are deleted
284  // in.
285  bool Changed = false;
286  for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(),
287       E = FunctionsToRemove.end(); I != E; ++I) {
288    resetCachedCostInfo((*I)->getFunction());
289    delete CG.removeFunctionFromModule(*I);
290    ++NumDeleted;
291    Changed = true;
292  }
293
294  return Changed;
295}
296