lib/Target/SparcV9/SparcV9PreSelection.cpp

//===- PreSelection.cpp - Specialize LLVM code for target machine ---------===//
// 
//                     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 file defines the PreSelection pass which specializes LLVM code for a
// target machine, while remaining in legal portable LLVM form and
// preserving type information and type safety.  This is meant to enable
// dataflow optimizations on target-specific operations such as accesses to
// constants, globals, and array indexing.
//
//===----------------------------------------------------------------------===//

#include "SparcInternals.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Module.h"
#include "llvm/Constants.h"
#include "llvm/iMemory.h"
#include "llvm/iPHINode.h"
#include "llvm/iOther.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Pass.h"
#include <algorithm>

namespace {

  //===--------------------------------------------------------------------===//
  // PreSelection Pass - Specialize LLVM code for the current target machine.
  // 
  class PreSelection : public Pass, public InstVisitor<PreSelection> {
    const TargetInstrInfo &instrInfo;
    Module *TheModule;

    std::map<const Constant*, GlobalVariable*> gvars;

    GlobalVariable* getGlobalForConstant(Constant* CV) {
      std::map<const Constant*, GlobalVariable*>::iterator I = gvars.find(CV);
      if (I != gvars.end()) return I->second;    // global exists so return it

      return I->second = new GlobalVariable(CV->getType(), true,
                                            GlobalValue::InternalLinkage, CV,
                                            "immcst", TheModule);
    }

  public:
    PreSelection(const TargetMachine &T)
      : instrInfo(T.getInstrInfo()), TheModule(0) {}

    // runOnBasicBlock - apply this pass to each BB
    bool run(Module &M) {
      TheModule = &M;

      // Build reverse map for pre-existing global constants so we can find them
      for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; ++I)
        if (I->hasInitializer() && I->isConstant())
          gvars[I->getInitializer()] = I;

      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
        visit(*I);

      gvars.clear();
      return true;
    }

    // These methods do the actual work of specializing code
    void visitInstruction(Instruction &I);   // common work for every instr. 
    void visitGetElementPtrInst(GetElementPtrInst &I);
    void visitCallInst(CallInst &I);
    void visitPHINode(PHINode &PN);

    // Helper functions for visiting operands of every instruction
    // 
    // visitOperands() works on every operand in [firstOp, lastOp-1].
    // If lastOp==0, lastOp defaults to #operands or #incoming Phi values.
    // 
    // visitOneOperand() does all the work for one operand.
    // 
    void visitOperands(Instruction &I, int firstOp=0);
    void visitOneOperand(Instruction &I, Value* Op, unsigned opNum,
                         Instruction& insertBefore);
  };

  // Register the pass...
  RegisterOpt<PreSelection> X("preselect",
                              "Specialize LLVM code for a target machine",
                              createPreSelectionPass);
}  // end anonymous namespace


//------------------------------------------------------------------------------
// Helper functions used by methods of class PreSelection
//------------------------------------------------------------------------------


// getGlobalAddr(): Put address of a global into a v. register.
static GetElementPtrInst* getGlobalAddr(Value* ptr, Instruction& insertBefore)
{
  if (isa<ConstantPointerRef>(ptr))
    ptr = cast<ConstantPointerRef>(ptr)->getValue();

  return (isa<GlobalVariable>(ptr))
    ? new GetElementPtrInst(ptr,
                    std::vector<Value*>(1, ConstantSInt::get(Type::LongTy, 0U)),
                    "addrOfGlobal", &insertBefore)
    : NULL;
}


// Wrapper on Constant::classof to use in find_if :-(
inline static bool nonConstant(const Use& U)
{
  return ! isa<Constant>(U);
}


static Instruction* DecomposeConstantExpr(ConstantExpr* CE,
                                          Instruction& insertBefore)
{
  Value *getArg1, *getArg2;

  switch(CE->getOpcode())
    {
    case Instruction::Cast:
      getArg1 = CE->getOperand(0);
      if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
        getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
      return new CastInst(getArg1, CE->getType(), "constantCast",&insertBefore);

    case Instruction::GetElementPtr:
      assert(find_if(CE->op_begin()+1, CE->op_end(),nonConstant) == CE->op_end()
             && "All indices in ConstantExpr getelementptr must be constant!");
      getArg1 = CE->getOperand(0);
      if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
        getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
      else if (GetElementPtrInst* gep = getGlobalAddr(getArg1, insertBefore))
        getArg1 = gep;
      return new GetElementPtrInst(getArg1,
                          std::vector<Value*>(CE->op_begin()+1, CE->op_end()),
                          "constantGEP", &insertBefore);

    default:                            // must be a binary operator
      assert(CE->getOpcode() >= Instruction::BinaryOpsBegin &&
             CE->getOpcode() <  Instruction::BinaryOpsEnd &&
             "Unrecognized opcode in ConstantExpr");
      getArg1 = CE->getOperand(0);
      if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
        getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
      getArg2 = CE->getOperand(1);
      if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg2))
        getArg2 = DecomposeConstantExpr(CEarg, insertBefore);
      return BinaryOperator::create((Instruction::BinaryOps) CE->getOpcode(),
                                    getArg1, getArg2,
                                    "constantBinaryOp", &insertBefore);
    }
}


//------------------------------------------------------------------------------
// Instruction visitor methods to perform instruction-specific operations
//------------------------------------------------------------------------------
inline void
PreSelection::visitOneOperand(Instruction &I, Value* Op, unsigned opNum,
                              Instruction& insertBefore)
{
  assert(&insertBefore != NULL && "Must have instruction to insert before.");

  if (GetElementPtrInst* gep = getGlobalAddr(Op, insertBefore)) {
    I.setOperand(opNum, gep);           // replace global operand
    return;                             // nothing more to do for this op.
  }

  Constant* CV  = dyn_cast<Constant>(Op);
  if (CV == NULL)
    return;

  if (ConstantExpr* CE = dyn_cast<ConstantExpr>(CV))
    { // load-time constant: factor it out so we optimize as best we can
      Instruction* computeConst = DecomposeConstantExpr(CE, insertBefore);
      I.setOperand(opNum, computeConst); // replace expr operand with result
    }
  else if (instrInfo.ConstantTypeMustBeLoaded(CV))
    { // load address of constant into a register, then load the constant
      GetElementPtrInst* gep = getGlobalAddr(getGlobalForConstant(CV),
                                             insertBefore);
      LoadInst* ldI = new LoadInst(gep, "loadConst", &insertBefore);
      I.setOperand(opNum, ldI);        // replace operand with copy in v.reg.
    }
  else if (instrInfo.ConstantMayNotFitInImmedField(CV, &I))
    { // put the constant into a virtual register using a cast
      CastInst* castI = new CastInst(CV, CV->getType(), "copyConst",
                                     &insertBefore);
      I.setOperand(opNum, castI);      // replace operand with copy in v.reg.
    }
}

// visitOperands() transforms individual operands of all instructions:
// -- Load "large" int constants into a virtual register.  What is large
//    depends on the type of instruction and on the target architecture.
// -- For any constants that cannot be put in an immediate field,
//    load address into virtual register first, and then load the constant.
// 
// firstOp and lastOp can be used to skip leading and trailing operands.
// If lastOp is 0, it defaults to #operands or #incoming Phi values.
//  
inline void PreSelection::visitOperands(Instruction &I, int firstOp) {
  // For any instruction other than PHI, copies go just before the instr.
  for (unsigned i = firstOp, e = I.getNumOperands(); i != e; ++i)
    visitOneOperand(I, I.getOperand(i), i, I);
}


void PreSelection::visitPHINode(PHINode &PN) {
  // For a PHI, operand copies must be before the terminator of the
  // appropriate predecessor basic block.  Remaining logic is simple
  // so just handle PHIs and other instructions separately.
  // 
  for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
    visitOneOperand(PN, PN.getIncomingValue(i),
                    PN.getOperandNumForIncomingValue(i),
                    *PN.getIncomingBlock(i)->getTerminator());
  // do not call visitOperands!
}



// Common work for *all* instructions.  This needs to be called explicitly
// by other visit<InstructionType> functions.
inline void
PreSelection::visitInstruction(Instruction &I)
{ 
  visitOperands(I);              // Perform operand transformations
}


// GetElementPtr instructions: check if pointer is a global
void
PreSelection::visitGetElementPtrInst(GetElementPtrInst &I)
{ 
  Instruction* curI = &I;

  // Decompose multidimensional array references
  if (I.getNumIndices() >= 2) {
    // DecomposeArrayRef() replaces I and deletes it, if successful,
    // so remember predecessor in order to find the replacement instruction.
    // Also remember the basic block in case there is no predecessor.
    Instruction* prevI = I.getPrev();
    BasicBlock* bb = I.getParent();
    if (DecomposeArrayRef(&I))
      // first instr. replacing I
      curI = cast<GetElementPtrInst>(prevI? prevI->getNext() : &bb->front());
  }

  // Perform other transformations common to all instructions
  visitInstruction(*curI);
}


void
PreSelection::visitCallInst(CallInst &I)
{
  // Tell visitOperands to ignore the function name if this is a direct call.
  visitOperands(I, (/*firstOp=*/ I.getCalledFunction()? 1 : 0));
}


//===----------------------------------------------------------------------===//
// createPreSelectionPass - Public entrypoint for pre-selection pass
// and this file as a whole...
//
Pass* createPreSelectionPass(TargetMachine &T) {
  return new PreSelection(T);
}