path: root/lib/Target/SparcV9/SparcV9PreSelection.cpp

//===- SparcV9PreSelection.cpp - Specialize LLVM code for SparcV9 ---------===//
// 
//                     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
// the SparcV9 instruction selector, while remaining in legal portable LLVM
// form and preserving type information and type safety. This is meant to enable
// dataflow optimizations on SparcV9-specific operations such as accesses to
// constants, globals, and array indexing.
//
//===----------------------------------------------------------------------===//

#include "SparcV9Internals.h"
#include "SparcV9BurgISel.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/Scalar.h"
#include <algorithm>
using namespace llvm;

namespace {

  //===--------------------------------------------------------------------===//
  // PreSelection Pass - Specialize LLVM code for the SparcV9 instr. selector.
  // 
  class PreSelection : public FunctionPass, public InstVisitor<PreSelection> {
    const TargetInstrInfo &instrInfo;

  public:
    PreSelection(const TargetMachine &T)
      : instrInfo(*T.getInstrInfo()) {}

    // runOnFunction - apply this pass to each Function
    bool runOnFunction(Function &F) {
      visit(F);
      return true;
    }
    const char *getPassName() const { return "SparcV9 Instr. Pre-selection"; }

    // 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);

    void visitBasicBlock(BasicBlock &BB) {
      if (isa<UnreachableInst>(BB.getTerminator())) {
        BB.getInstList().pop_back();
        const Type *RetTy = BB.getParent()->getReturnType();
        Value *RetVal = RetTy == Type::VoidTy ? 0 : UndefValue::get(RetTy);
        new ReturnInst(RetVal, &BB);
      }
    }

    // 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);
  };

#if 0
  // Register the pass...
  RegisterPass<PreSelection> X("preselect",
                               "Specialize LLVM code for a target machine"
                               createPreselectionPass);
#endif

}  // 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) {

  return (isa<GlobalVariable>(ptr))
    ? new GetElementPtrInst(ptr,
                    std::vector<Value*>(1, ConstantSInt::get(Type::LongTy, 0U)),
                    "addrOfGlobal:" + ptr->getName(), &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:" + getArg1->getName(), &insertBefore);
                          
    case Instruction::Select: {
      Value *C, *S1, *S2;
      C = CE->getOperand (0);
      if (ConstantExpr* CEarg = dyn_cast<ConstantExpr> (C))
        C = DecomposeConstantExpr (CEarg, insertBefore);
      S1 = CE->getOperand (1);
      if (ConstantExpr* CEarg = dyn_cast<ConstantExpr> (S1))
        S1 = DecomposeConstantExpr (CEarg, insertBefore);
      S2 = CE->getOperand (2);
      if (ConstantExpr* CEarg = dyn_cast<ConstantExpr> (S2))
        S2 = DecomposeConstantExpr (CEarg, insertBefore);
      return new SelectInst (C, S1, S2, "constantSelect", &insertBefore);
    }
    
    default:                            // must be a binary operator
      assert(CE->getOpcode() >= Instruction::BinaryOpsBegin &&
             CE->getOpcode() <  Instruction::BinaryOpsEnd &&
             "Unhandled 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);
    }
}

static inline bool ConstantTypeMustBeLoaded(const Type* CVT) {
  assert(CVT->isPrimitiveType() || isa<PointerType>(CVT));
  return !(CVT->isIntegral() || isa<PointerType>(CVT));
}

//------------------------------------------------------------------------------
// 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 (ConstantTypeMustBeLoaded(CV->getType())) {
    // load address of constant into a register, then load the constant
    // this is now done during instruction selection
    // the constant will live in the MachineConstantPool later on
  } else if (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 - transform 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 visi