Inliner.cpp revision d1586b1a1d27d5efeb8e487bbeb7ed255159e53b 
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/InlineCost.h"
25#include "llvm/Transforms/Utils/Cloning.h"
26#include "llvm/Support/CommandLine.h"
27#include "llvm/Support/Debug.h"
28#include "llvm/Support/raw_ostream.h"
29#include "llvm/ADT/SmallPtrSet.h"
30#include "llvm/ADT/Statistic.h"
31#include <set>
32using namespace llvm;
33
34STATISTIC(NumInlined, "Number of functions inlined");
35STATISTIC(NumDeleted, "Number of functions deleted because all callers found");
36
37static cl::opt<int>
38InlineLimit("inline-threshold", cl::Hidden, cl::init(200), cl::ZeroOrMore,
39        cl::desc("Control the amount of inlining to perform (default = 200)"));
40
41Inliner::Inliner(void *ID)
42  : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {}
43
44Inliner::Inliner(void *ID, int Threshold)
45  : CallGraphSCCPass(ID), InlineThreshold(Threshold) {}
46
47/// getAnalysisUsage - For this class, we declare that we require and preserve
48/// the call graph.  If the derived class implements this method, it should
49/// always explicitly call the implementation here.
50void Inliner::getAnalysisUsage(AnalysisUsage &Info) const {
51  CallGraphSCCPass::getAnalysisUsage(Info);
52}
53
54// InlineCallIfPossible - If it is possible to inline the specified call site,
55// do so and update the CallGraph for this operation.
56bool Inliner::InlineCallIfPossible(CallSite CS, CallGraph &CG,
57                                 const SmallPtrSet<Function*, 8> &SCCFunctions,
58                                 const TargetData *TD) {
59  Function *Callee = CS.getCalledFunction();
60  Function *Caller = CS.getCaller();
61
62  if (!InlineFunction(CS, &CG, TD))
63    return false;
64
65  // If the inlined function had a higher stack protection level than the
66  // calling function, then bump up the caller's stack protection level.
67  if (Callee->hasFnAttr(Attribute::StackProtectReq))
68    Caller->addFnAttr(Attribute::StackProtectReq);
69  else if (Callee->hasFnAttr(Attribute::StackProtect) &&
70           !Caller->hasFnAttr(Attribute::StackProtectReq))
71    Caller->addFnAttr(Attribute::StackProtect);
72
73  // If we inlined the last possible call site to the function, delete the
74  // function body now.
75  if (Callee->use_empty() &&
76      (Callee->hasLocalLinkage() || Callee->hasAvailableExternallyLinkage()) &&
77      !SCCFunctions.count(Callee)) {
78    DEBUG(errs() << "    -> Deleting dead function: "
79          << Callee->getName() << "\n");
80    CallGraphNode *CalleeNode = CG[Callee];
81
82    // Remove any call graph edges from the callee to its callees.
83    CalleeNode->removeAllCalledFunctions();
84
85    resetCachedCostInfo(CalleeNode->getFunction());
86
87    // Removing the node for callee from the call graph and delete it.
88    delete CG.removeFunctionFromModule(CalleeNode);
89    ++NumDeleted;
90  }
91  return true;
92}
93
94/// shouldInline - Return true if the inliner should attempt to inline
95/// at the given CallSite.
96bool Inliner::shouldInline(CallSite CS) {
97  InlineCost IC = getInlineCost(CS);
98
99  if (IC.isAlways()) {
100    DEBUG(errs() << "    Inlining: cost=always"
101          << ", Call: " << *CS.getInstruction() << "\n");
102    return true;
103  }
104
105  if (IC.isNever()) {
106    DEBUG(errs() << "    NOT Inlining: cost=never"
107          << ", Call: " << *CS.getInstruction() << "\n");
108    return false;
109  }
110
111  int Cost = IC.getValue();
112  int CurrentThreshold = InlineThreshold;
113  Function *Fn = CS.getCaller();
114  if (Fn && !Fn->isDeclaration() &&
115      Fn->hasFnAttr(Attribute::OptimizeForSize) &&
116      InlineThreshold != 50)
117    CurrentThreshold = 50;
118
119  float FudgeFactor = getInlineFudgeFactor(CS);
120  if (Cost >= (int)(CurrentThreshold * FudgeFactor)) {
121    DEBUG(errs() << "    NOT Inlining: cost=" << Cost
122          << ", Call: " << *CS.getInstruction() << "\n");
123    return false;
124  }
125
126  DEBUG(errs() << "    Inlining: cost=" << Cost
127        << ", Call: " << *CS.getInstruction() << "\n");
128  return true;
129}
130
131bool Inliner::runOnSCC(const std::vector<CallGraphNode*> &SCC) {
132  CallGraph &CG = getAnalysis<CallGraph>();
133  const TargetData *TD = getAnalysisIfAvailable<TargetData>();
134
135  SmallPtrSet<Function*, 8> SCCFunctions;
136  DEBUG(errs() << "Inliner visiting SCC:");
137  for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
138    Function *F = SCC[i]->getFunction();
139    if (F) SCCFunctions.insert(F);
140    DEBUG(errs() << " " << (F ? F->getName() : "INDIRECTNODE"));
141  }
142
143  // Scan through and identify all call sites ahead of time so that we only
144  // inline call sites in the original functions, not call sites that result
145  // from inlining other functions.
146  std::vector<CallSite> CallSites;
147
148  for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
149    Function *F = SCC[i]->getFunction();
150    if (!F) continue;
151
152    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
153      for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
154        CallSite CS = CallSite::get(I);
155        if (CS.getInstruction() == 0 || isa<DbgInfoIntrinsic>(I))
156          continue;
157
158        if (CS.getCalledFunction() == 0 ||
159            !CS.getCalledFunction()->isDeclaration())
160          CallSites.push_back(CS);
161      }
162  }
163
164  DEBUG(errs() << ": " << CallSites.size() << " call sites.\n");
165
166  // Now that we have all of the call sites, move the ones to functions in the
167  // current SCC to the end of the list.
168  unsigned FirstCallInSCC = CallSites.size();
169  for (unsigned i = 0; i < FirstCallInSCC; ++i)
170    if (Function *F = CallSites[i].getCalledFunction())
171      if (SCCFunctions.count(F))
172        std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);
173
174  // Now that we have all of the call sites, loop over them and inline them if
175  // it looks profitable to do so.
176  bool Changed = false;
177  bool LocalChange;
178  do {
179    LocalChange = false;
180    // Iterate over the outer loop because inlining functions can cause indirect
181    // calls to become direct calls.
182    for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
183      // We can only inline direct calls.
184      Function *Callee = CallSites[CSi].getCalledFunction();
185      if (!Callee) continue;
186
187      // Calls to external functions are never inlinable.
188      if (Callee->isDeclaration()) {
189        if (SCC.size() == 1) {
190          std::swap(CallSites[CSi], CallSites.back());
191          CallSites.pop_back();
192        } else {
193          // Keep the 'in SCC / not in SCC' boundary correct.
194          CallSites.erase(CallSites.begin()+CSi);
195        }
196        --CSi;
197        continue;
198      }
199
200      // If the policy determines that we should inline this function,
201      // try to do so.
202      CallSite CS = CallSites[CSi];
203      if (!shouldInline(CS))
204        continue;
205
206      Function *Caller = CS.getCaller();
207      // Attempt to inline the function...
208      if (!InlineCallIfPossible(CS, CG, SCCFunctions, TD))
209        continue;
210
211      // Remove any cached cost info for this caller, as inlining the
212      // callee has increased the size of the caller (which may be the
213      // same as the callee).
214      resetCachedCostInfo(Caller);
215
216      // Remove this call site from the list.  If possible, use
217      // swap/pop_back for efficiency, but do not use it if doing so would
218      // move a call site to a function in this SCC before the
219      // 'FirstCallInSCC' barrier.
220      if (SCC.size() == 1) {
221        std::swap(CallSites[CSi], CallSites.back());
222        CallSites.pop_back();
223      } else {
224        CallSites.erase(CallSites.begin()+CSi);
225      }
226      --CSi;
227
228      ++NumInlined;
229      Changed = true;
230      LocalChange = true;
231    }
232  } while (LocalChange);
233
234  return Changed;
235}
236
237// doFinalization - Remove now-dead linkonce functions at the end of
238// processing to avoid breaking the SCC traversal.
239bool Inliner::doFinalization(CallGraph &CG) {
240  return removeDeadFunctions(CG);
241}
242
243/// removeDeadFunctions - Remove dead functions that are not included in
244/// DNR (Do Not Remove) list.
245bool Inliner::removeDeadFunctions(CallGraph &CG,
246                                  SmallPtrSet<const Function *, 16> *DNR) {
247  SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove;
248
249  // Scan for all of the functions, looking for ones that should now be removed
250  // from the program.  Insert the dead ones in the FunctionsToRemove set.
251  for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
252    CallGraphNode *CGN = I->second;
253    if (CGN == 0 || CGN->getFunction() == 0)
254      continue;
255
256    Function *F = CGN->getFunction();
257
258    // If the only remaining users of the function are dead constants, remove
259    // them.
260    F->removeDeadConstantUsers();
261
262    if (DNR && DNR->count(F))
263      continue;
264    if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage())
265      continue;
266    if (!F->use_empty())
267      continue;
268
269    // Remove any call graph edges from the function to its callees.
270    CGN->removeAllCalledFunctions();
271
272    // Remove any edges from the external node to the function's call graph
273    // node.  These edges might have been made irrelegant due to
274    // optimization of the program.
275    CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);
276
277    // Removing the node for callee from the call graph and delete it.
278    FunctionsToRemove.insert(CGN);
279  }
280
281  // Now that we know which functions to delete, do so.  We didn't want to do
282  // this inline, because that would invalidate our CallGraph::iterator
283  // objects. :(
284  //
285  // Note that it doesn't matter that we are iterating over a non-stable set
286  // here to do this, it doesn't matter which order the functions are deleted
287  // in.
288  bool Changed = false;
289  for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(),
290       E = FunctionsToRemove.end(); I != E; ++I) {
291    resetCachedCostInfo((*I)->getFunction());
292    delete CG.removeFunctionFromModule(*I);
293    ++NumDeleted;
294    Changed = true;
295  }
296
297  return Changed;
298}
299