Inliner.cpp

//===- Inliner.cpp - Code common to all inliners --------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the mechanics required to implement inlining without
// missing any calls and updating the call graph.  The decisions of which calls
// are profitable to inline are implemented elsewhere.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "inline"
#include "llvm/Module.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/IPO/InlinerPass.h"
#include "llvm/Transforms/Utils/InlineCost.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include <set>
using namespace llvm;

STATISTIC(NumInlined, "Number of functions inlined");
STATISTIC(NumDeleted, "Number of functions deleted because all callers found");

static cl::opt<int>
InlineLimit("inline-threshold", cl::Hidden, cl::init(200), cl::ZeroOrMore,
        cl::desc("Control the amount of inlining to perform (default = 200)"));

Inliner::Inliner(void *ID) 
  : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {}

Inliner::Inliner(void *ID, int Threshold) 
  : CallGraphSCCPass(ID), InlineThreshold(Threshold) {}

/// getAnalysisUsage - For this class, we declare that we require and preserve
/// the call graph.  If the derived class implements this method, it should
/// always explicitly call the implementation here.
void Inliner::getAnalysisUsage(AnalysisUsage &Info) const {
  CallGraphSCCPass::getAnalysisUsage(Info);
}

// InlineCallIfPossible - If it is possible to inline the specified call site,
// do so and update the CallGraph for this operation.
bool Inliner::InlineCallIfPossible(CallSite CS, CallGraph &CG,
                                 const SmallPtrSet<Function*, 8> &SCCFunctions,
                                 const TargetData *TD) {
  Function *Callee = CS.getCalledFunction();
  Function *Caller = CS.getCaller();

  if (!InlineFunction(CS, &CG, TD))
    return false;

  // If the inlined function had a higher stack protection level than the
  // calling function, then bump up the caller's stack protection level.
  if (Callee->hasFnAttr(Attribute::StackProtectReq))
    Caller->addFnAttr(Attribute::StackProtectReq);
  else if (Callee->hasFnAttr(Attribute::StackProtect) &&
           !Caller->hasFnAttr(Attribute::StackProtectReq))
    Caller->addFnAttr(Attribute::StackProtect);

  // If we inlined the last possible call site to the function, delete the
  // function body now.
  if (Callee->use_empty() && 
      (Callee->hasLocalLinkage() || Callee->hasAvailableExternallyLinkage()) &&
      !SCCFunctions.count(Callee)) {
    DEBUG(errs() << "    -> Deleting dead function: " 
          << Callee->getName() << "\n");
    CallGraphNode *CalleeNode = CG[Callee];

    // Remove any call graph edges from the callee to its callees.
    CalleeNode->removeAllCalledFunctions();

    resetCachedCostInfo(CalleeNode->getFunction());

    // Removing the node for callee from the call graph and delete it.
    delete CG.removeFunctionFromModule(CalleeNode);
    ++NumDeleted;
  }
  return true;
}
        
/// shouldInline - Return true if the inliner should attempt to inline
/// at the given CallSite.
bool Inliner::shouldInline(CallSite CS) {
  InlineCost IC = getInlineCost(CS);
  
  if (IC.isAlways()) {
    DEBUG(errs() << "    Inlining: cost=always"
          << ", Call: " << *CS.getInstruction() << "\n");
    return true;
  }
  
  if (IC.isNever()) {
    DEBUG(errs() << "    NOT Inlining: cost=never"
          << ", Call: " << *CS.getInstruction() << "\n");
    return false;
  }
  
  int Cost = IC.getValue();
  int CurrentThreshold = InlineThreshold;
  Function *Fn = CS.getCaller();
  if (Fn && !Fn->isDeclaration() &&
      Fn->hasFnAttr(Attribute::OptimizeForSize) &&
      InlineThreshold != 50)
    CurrentThreshold = 50;
  
  float FudgeFactor = getInlineFudgeFactor(CS);
  if (Cost >= (int)(CurrentThreshold * FudgeFactor)) {
    DEBUG(errs() << "    NOT Inlining: cost=" << Cost
          << ", Call: " << *CS.getInstruction() << "\n");
    return false;
  }
  
  DEBUG(errs() << "    Inlining: cost=" << Cost
        << ", Call: " << *CS.getInstruction() << "\n");
  return true;
}

bool Inliner::runOnSCC(const std::vector<CallGraphNode*> &SCC) {
  CallGraph &CG = getAnalysis<CallGraph>();
  const TargetData *TD = getAnalysisIfAvailable<TargetData>();

  SmallPtrSet<Function*, 8> SCCFunctions;
  DEBUG(errs() << "Inliner visiting SCC:");
  for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
    Function *F = SCC[i]->getFunction();
    if (F) SCCFunctions.insert(F);
    DEBUG(errs() << " " << (F ? F->getName() : "INDIRECTNODE"));
  }

  // Scan through and identify all call sites ahead of time so that we only
  // inline call sites in the original functions, not call sites that result
  // from inlining other functions.
  std::vector<CallSite> CallSites;

  for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
    Function *F = SCC[i]->getFunction();
    if (!F) continue;
    
    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
      for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
        CallSite CS = CallSite::get(I);
        if (CS.getInstruction() == 0 || isa<DbgInfoIntrinsic>(I))
          continue;
        
        if (CS.getCalledFunction() == 0 ||
            !CS.getCalledFunction()->isDeclaration())
          CallSites.push_back(CS);
      }
  }

  DEBUG(errs() << ": " << CallSites.size() << " call sites.\n");

  // Now that we have all of the call sites, move the ones to functions in the
  // current SCC to the end of the list.
  unsigned FirstCallInSCC = CallSites.size();
  for (unsigned i = 0; i < FirstCallInSCC; ++i)
    if (Function *F = CallSites[i].getCalledFunction())
      if (SCCFunctions.count(F))
        std::swap(CallSites[i--], CallSites[--FirstCallInSCC]);

  // Now that we have all of the call sites, loop over them and inline them if
  // it looks profitable to do so.
  bool Changed = false;
  bool LocalChange;
  do {
    LocalChange = false;
    // Iterate over the outer loop because inlining functions can cause indirect
    // calls to become direct calls.
    for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
      // We can only inline direct calls.
      Function *Callee = CallSites[CSi].getCalledFunction();
      if (!Callee) continue;
      
      // Calls to external functions are never inlinable.
      if (Callee->isDeclaration()) {
        if (SCC.size() == 1) {
          std::swap(CallSites[CSi], CallSites.back());
          CallSites.pop_back();
        } else {
          // Keep the 'in SCC / not in SCC' boundary correct.
          CallSites.erase(CallSites.begin()+CSi);
        }
        --CSi;
        continue;
      }

      // If the policy determines that we should inline this function,
      // try to do so.
      CallSite CS = CallSites[CSi];
      if (!shouldInline(CS))
        continue;
      
      Function *Caller = CS.getCaller();
      // Attempt to inline the function...
      if (!InlineCallIfPossible(CS, CG, SCCFunctions, TD))
        continue;
      
      // Remove any cached cost info for this caller, as inlining the
      // callee has increased the size of the caller (which may be the
      // same as the callee).
      resetCachedCostInfo(Caller);

      // Remove this call site from the list.  If possible, use 
      // swap/pop_back for efficiency, but do not use it if doing so would
      // move a call site to a function in this SCC before the
      // 'FirstCallInSCC' barrier.
      if (SCC.size() == 1) {
        std::swap(CallSites[CSi], CallSites.back());
        CallSites.pop_back();
      } else {
        CallSites.erase(CallSites.begin()+CSi);
      }
      --CSi;

      ++NumInlined;
      Changed = true;
      LocalChange = true;
    }
  } while (LocalChange);

  return Changed;
}

// doFinalization - Remove now-dead linkonce functions at the end of
// processing to avoid breaking the SCC traversal.
bool Inliner::doFinalization(CallGraph &CG) {
  return removeDeadFunctions(CG);
}

/// removeDeadFunctions - Remove dead functions that are not included in
/// DNR (Do Not Remove) list.
bool Inliner::removeDeadFunctions(CallGraph &CG, 
                                  SmallPtrSet<const Function *, 16> *DNR) {
  SmallPtrSet<CallGraphNode*, 16> FunctionsToRemove;

  // Scan for all of the functions, looking for ones that should now be removed
  // from the program.  Insert the dead ones in the FunctionsToRemove set.
  for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
    CallGraphNode *CGN = I->second;
    if (CGN == 0 || CGN->getFunction() == 0)
      continue;
    
    Function *F = CGN->getFunction();
    
    // If the only remaining users of the function are dead constants, remove
    // them.
    F->removeDeadConstantUsers();

    if (DNR && DNR->count(F))
      continue;
    if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage())
      continue;
    if (!F->use_empty())
      continue;
    
    // Remove any call graph edges from the function to its callees.
    CGN->removeAllCalledFunctions();

    // Remove any edges from the external node to the function's call graph
    // node.  These edges might have been made irrelegant due to
    // optimization of the program.
    CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);

    // Removing the node for callee from the call graph and delete it.
    FunctionsToRemove.insert(CGN);
  }

  // Now that we know which functions to delete, do so.  We didn't want to do
  // this inline, because that would invalidate our CallGraph::iterator
  // objects. :(
  //
  // Note that it doesn't matter that we are iterating over a non-stable set
  // here to do this, it doesn't matter which order the functions are deleted
  // in.
  bool Changed = false;
  for (SmallPtrSet<CallGraphNode*, 16>::iterator I = FunctionsToRemove.begin(),
       E = FunctionsToRemove.end(); I != E; ++I) {
    resetCachedCostInfo((*I)->getFunction());
    delete CG.removeFunctionFromModule(*I);
    ++NumDeleted;
    Changed = true;
  }

  return Changed;
}