<commit_before>//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This transformation implements the well known scalar replacement of
// aggregates transformation.  This xform breaks up alloca instructions of
// aggregate type (structure or array) into individual alloca instructions for
// each member (if possible).  Then, if possible, it transforms the individual
// alloca instructions into nice clean scalar SSA form.
//
// This combines a simple SRoA algorithm with the Mem2Reg algorithm because
// often interact, especially for C++ programs.  As such, iterating between
// SRoA, then Mem2Reg until we run out of things to promote works well.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Pass.h"
#include "llvm/iMemory.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include "Support/StringExtras.h"
using namespace llvm;

namespace {
  Statistic<> NumReplaced("scalarrepl", "Number of allocas broken up");
  Statistic<> NumPromoted("scalarrepl", "Number of allocas promoted");

  struct SROA : public FunctionPass {
    bool runOnFunction(Function &F);

    bool performScalarRepl(Function &F);
    bool performPromotion(Function &F);

    // getAnalysisUsage - This pass does not require any passes, but we know it
    // will not alter the CFG, so say so.
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<DominatorTree>();
      AU.addRequired<DominanceFrontier>();
      AU.addRequired<TargetData>();
      AU.setPreservesCFG();
    }

  private:
    bool isSafeElementUse(Value *Ptr);
    bool isSafeUseOfAllocation(Instruction *User);
    bool isSafeAllocaToPromote(AllocationInst *AI);
    AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base);
  };

  RegisterOpt<SROA> X("scalarrepl", "Scalar Replacement of Aggregates");
}

// Public interface to the ScalarReplAggregates pass
Pass *llvm::createScalarReplAggregatesPass() { return new SROA(); }


bool SROA::runOnFunction(Function &F) {
  bool Changed = performPromotion(F);
  while (1) {
    bool LocalChange = performScalarRepl(F);
    if (!LocalChange) break;   // No need to repromote if no scalarrepl
    Changed = true;
    LocalChange = performPromotion(F);
    if (!LocalChange) break;   // No need to re-scalarrepl if no promotion
  }

  return Changed;
}


bool SROA::performPromotion(Function &F) {
  std::vector<AllocaInst*> Allocas;
  const TargetData &TD = getAnalysis<TargetData>();
  DominatorTree     &DT = getAnalysis<DominatorTree>();
  DominanceFrontier &DF = getAnalysis<DominanceFrontier>();

  BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function

  bool Changed = false;
  
  while (1) {
    Allocas.clear();

    // Find allocas that are safe to promote, by looking at all instructions in
    // the entry node
    for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
      if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
        if (isAllocaPromotable(AI, TD))
          Allocas.push_back(AI);

    if (Allocas.empty()) break;

    PromoteMemToReg(Allocas, DT, DF, TD);
    NumPromoted += Allocas.size();
    Changed = true;
  }

  return Changed;
}


// performScalarRepl - This algorithm is a simple worklist driven algorithm,
// which runs on all of the malloc/alloca instructions in the function, removing
// them if they are only used by getelementptr instructions.
//
bool SROA::performScalarRepl(Function &F) {
  std::vector<AllocationInst*> WorkList;

  // Scan the entry basic block, adding any alloca's and mallocs to the worklist
  BasicBlock &BB = F.getEntryBlock();
  for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
    if (AllocationInst *A = dyn_cast<AllocationInst>(I))
      WorkList.push_back(A);

  // Process the worklist
  bool Changed = false;
  while (!WorkList.empty()) {
    AllocationInst *AI = WorkList.back();
    WorkList.pop_back();

    // We cannot transform the allocation instruction if it is an array
    // allocation (allocations OF arrays are ok though), and an allocation of a
    // scalar value cannot be decomposed at all.
    //
    if (AI->isArrayAllocation() ||
        (!isa<StructType>(AI->getAllocatedType()) &&
         !isa<ArrayType>(AI->getAllocatedType()))) continue;

    // Check that all of the users of the allocation are capable of being
    // transformed.
    if (!isSafeAllocaToPromote(AI))
      continue;

    DEBUG(std::cerr << "Found inst to xform: " << *AI);
    Changed = true;
    
    std::vector<AllocaInst*> ElementAllocas;
    if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
      ElementAllocas.reserve(ST->getNumContainedTypes());
      for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
        AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0,
                                        AI->getName() + "." + utostr(i), AI);
        ElementAllocas.push_back(NA);
        WorkList.push_back(NA);  // Add to worklist for recursive processing
      }
    } else {
      const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
      ElementAllocas.reserve(AT->getNumElements());
      const Type *ElTy = AT->getElementType();
      for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
        AllocaInst *NA = new AllocaInst(ElTy, 0,
                                        AI->getName() + "." + utostr(i), AI);
        ElementAllocas.push_back(NA);
        WorkList.push_back(NA);  // Add to worklist for recursive processing
      }
    }
    
    // Now that we have created the alloca instructions that we want to use,
    // expand the getelementptr instructions to use them.
    //
    for (Value::use_iterator I = AI->use_begin(), E = AI->use_end();
         I != E; ++I) {
      Instruction *User = cast<Instruction>(*I);<commit_msg>Do not loop over uses as we delete them.  This causes iterators to be invalidated out from under us.  This bug goes back to revision 1.1: scary.<commit_after>//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This transformation implements the well known scalar replacement of
// aggregates transformation.  This xform breaks up alloca instructions of
// aggregate type (structure or array) into individual alloca instructions for
// each member (if possible).  Then, if possible, it transforms the individual
// alloca instructions into nice clean scalar SSA form.
//
// This combines a simple SRoA algorithm with the Mem2Reg algorithm because
// often interact, especially for C++ programs.  As such, iterating between
// SRoA, then Mem2Reg until we run out of things to promote works well.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/Pass.h"
#include "llvm/iMemory.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include "Support/StringExtras.h"
using namespace llvm;

namespace {
  Statistic<> NumReplaced("scalarrepl", "Number of allocas broken up");
  Statistic<> NumPromoted("scalarrepl", "Number of allocas promoted");

  struct SROA : public FunctionPass {
    bool runOnFunction(Function &F);

    bool performScalarRepl(Function &F);
    bool performPromotion(Function &F);

    // getAnalysisUsage - This pass does not require any passes, but we know it
    // will not alter the CFG, so say so.
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<DominatorTree>();
      AU.addRequired<DominanceFrontier>();
      AU.addRequired<TargetData>();
      AU.setPreservesCFG();
    }

  private:
    bool isSafeElementUse(Value *Ptr);
    bool isSafeUseOfAllocation(Instruction *User);
    bool isSafeAllocaToPromote(AllocationInst *AI);
    AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base);
  };

  RegisterOpt<SROA> X("scalarrepl", "Scalar Replacement of Aggregates");
}

// Public interface to the ScalarReplAggregates pass
Pass *llvm::createScalarReplAggregatesPass() { return new SROA(); }


bool SROA::runOnFunction(Function &F) {
  bool Changed = performPromotion(F);
  while (1) {
    bool LocalChange = performScalarRepl(F);
    if (!LocalChange) break;   // No need to repromote if no scalarrepl
    Changed = true;
    LocalChange = performPromotion(F);
    if (!LocalChange) break;   // No need to re-scalarrepl if no promotion
  }

  return Changed;
}


bool SROA::performPromotion(Function &F) {
  std::vector<AllocaInst*> Allocas;
  const TargetData &TD = getAnalysis<TargetData>();
  DominatorTree     &DT = getAnalysis<DominatorTree>();
  DominanceFrontier &DF = getAnalysis<DominanceFrontier>();

  BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function

  bool Changed = false;
  
  while (1) {
    Allocas.clear();

    // Find allocas that are safe to promote, by looking at all instructions in
    // the entry node
    for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
      if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
        if (isAllocaPromotable(AI, TD))
          Allocas.push_back(AI);

    if (Allocas.empty()) break;

    PromoteMemToReg(Allocas, DT, DF, TD);
    NumPromoted += Allocas.size();
    Changed = true;
  }

  return Changed;
}


// performScalarRepl - This algorithm is a simple worklist driven algorithm,
// which runs on all of the malloc/alloca instructions in the function, removing
// them if they are only used by getelementptr instructions.
//
bool SROA::performScalarRepl(Function &F) {
  std::vector<AllocationInst*> WorkList;

  // Scan the entry basic block, adding any alloca's and mallocs to the worklist
  BasicBlock &BB = F.getEntryBlock();
  for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
    if (AllocationInst *A = dyn_cast<AllocationInst>(I))
      WorkList.push_back(A);

  // Process the worklist
  bool Changed = false;
  while (!WorkList.empty()) {
    AllocationInst *AI = WorkList.back();
    WorkList.pop_back();

    // We cannot transform the allocation instruction if it is an array
    // allocation (allocations OF arrays are ok though), and an allocation of a
    // scalar value cannot be decomposed at all.
    //
    if (AI->isArrayAllocation() ||
        (!isa<StructType>(AI->getAllocatedType()) &&
         !isa<ArrayType>(AI->getAllocatedType()))) continue;

    // Check that all of the users of the allocation are capable of being
    // transformed.
    if (!isSafeAllocaToPromote(AI))
      continue;

    DEBUG(std::cerr << "Found inst to xform: " << *AI);
    Changed = true;
    
    std::vector<AllocaInst*> ElementAllocas;
    if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
      ElementAllocas.reserve(ST->getNumContainedTypes());
      for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
        AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0,
                                        AI->getName() + "." + utostr(i), AI);
        ElementAllocas.push_back(NA);
        WorkList.push_back(NA);  // Add to worklist for recursive processing
      }
    } else {
      const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
      ElementAllocas.reserve(AT->getNumElements());
      const Type *ElTy = AT->getElementType();
      for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
        AllocaInst *NA = new AllocaInst(ElTy, 0,
                                        AI->getName() + "." + utostr(i), AI);
        ElementAllocas.push_back(NA);
        WorkList.push_back(NA);  // Add to worklist for recursive processing
      }
    }
    
    // Now that we have created the alloca instructions that we want to use,
    // expand the getelementptr instructions to use them.
    //
    while (!AI->use_empty()) {
      Instruction *User = cast<Instruction>(AI->use_back());
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