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llvm-6502/lib/CodeGen/InstrSelection/InstrSelectionSupport.cpp
Vikram S. Adve cf911de3c6 Significant improvement: GEP used by a load or store no longer generates 
a separate ADD; instead just use the indexed load/store instruction!
Also, a bug fix: folding a GEP with a leading non-zero index with
its predecessor was incorrect: now it only happens if the predecessor
is pointing to an indexable type (aka SequentialType).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4168 91177308-0d34-0410-b5e6-96231b3b80d8
2002-10-14 16:30:55 +00:00

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//===-- InstrSelectionSupport.cpp -----------------------------------------===//
//
// Target-independent instruction selection code. See SparcInstrSelection.cpp
// for usage.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/InstrSelectionSupport.h"
#include "llvm/CodeGen/InstrSelection.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrAnnot.h"
#include "llvm/CodeGen/MachineCodeForInstruction.h"
#include "llvm/CodeGen/MachineCodeForMethod.h"
#include "llvm/CodeGen/InstrForest.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/MachineRegInfo.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/Type.h"
#include "llvm/iMemory.h"
using std::vector;
//*************************** Local Functions ******************************/
// Generate code to load the constant into a TmpInstruction (virtual reg) and
// returns the virtual register.
//
static TmpInstruction*
InsertCodeToLoadConstant(Function *F,
Value* opValue,
Instruction* vmInstr,
vector<MachineInstr*>& loadConstVec,
TargetMachine& target)
{
// Create a tmp virtual register to hold the constant.
TmpInstruction* tmpReg = new TmpInstruction(opValue);
MachineCodeForInstruction &mcfi = MachineCodeForInstruction::get(vmInstr);
mcfi.addTemp(tmpReg);
target.getInstrInfo().CreateCodeToLoadConst(target, F, opValue, tmpReg,
loadConstVec, mcfi);
// Record the mapping from the tmp VM instruction to machine instruction.
// Do this for all machine instructions that were not mapped to any
// other temp values created by
// tmpReg->addMachineInstruction(loadConstVec.back());
return tmpReg;
}
//---------------------------------------------------------------------------
// Function GetConstantValueAsUnsignedInt
// Function GetConstantValueAsSignedInt
//
// Convenience functions to get the value of an integral constant, for an
// appropriate integer or non-integer type that can be held in a signed
// or unsigned integer respectively. The type of the argument must be
// the following:
// Signed or unsigned integer
// Boolean
// Pointer
//
// isValidConstant is set to true if a valid constant was found.
//---------------------------------------------------------------------------
uint64_t
GetConstantValueAsUnsignedInt(const Value *V,
bool &isValidConstant)
{
isValidConstant = true;
if (isa<Constant>(V))
if (const ConstantBool *CB = dyn_cast<ConstantBool>(V))
return (int64_t)CB->getValue();
else if (const ConstantSInt *CS = dyn_cast<ConstantSInt>(V))
return (uint64_t)CS->getValue();
else if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(V))
return CU->getValue();
isValidConstant = false;
return 0;
}
int64_t
GetConstantValueAsSignedInt(const Value *V,
bool &isValidConstant)
{
uint64_t C = GetConstantValueAsUnsignedInt(V, isValidConstant);
if (isValidConstant) {
if (V->getType()->isSigned() || C < INT64_MAX) // safe to cast to signed
return (int64_t) C;
else
isValidConstant = false;
}
return 0;
}
//---------------------------------------------------------------------------
// Function: FoldGetElemChain
//
// Purpose:
// Fold a chain of GetElementPtr instructions containing only
// constant offsets into an equivalent (Pointer, IndexVector) pair.
// Returns the pointer Value, and stores the resulting IndexVector
// in argument chainIdxVec. This is a helper function for
// FoldConstantIndices that does the actual folding.
//---------------------------------------------------------------------------
// Check for a constant 0.
inline bool
IsZero(Value* idx)
{
return (idx == ConstantSInt::getNullValue(idx->getType()));
}
static Value*
FoldGetElemChain(InstrTreeNode* ptrNode, vector<Value*>& chainIdxVec,
bool lastInstHasLeadingNonZero)
{
InstructionNode* gepNode = dyn_cast<InstructionNode>(ptrNode);
GetElementPtrInst* gepInst =
dyn_cast_or_null<GetElementPtrInst>(gepNode ? gepNode->getInstruction() :0);
// ptr value is not computed in this tree or ptr value does not come from GEP
// instruction
if (gepInst == NULL)
return NULL;
// Return NULL if we don't fold any instructions in.
Value* ptrVal = NULL;
// Now chase the chain of getElementInstr instructions, if any.
// Check for any non-constant indices and stop there.
// Also, stop if the first index of child is a non-zero array index
// and the last index of the current node is a non-array index:
// in that case, a non-array declared type is being accessed as an array
// which is not type-safe, but could be legal.
//
InstructionNode* ptrChild = gepNode;
while (ptrChild && (ptrChild->getOpLabel() == Instruction::GetElementPtr ||
ptrChild->getOpLabel() == GetElemPtrIdx))
{
// Child is a GetElemPtr instruction
gepInst = cast<GetElementPtrInst>(ptrChild->getValue());
User::op_iterator OI, firstIdx = gepInst->idx_begin();
User::op_iterator lastIdx = gepInst->idx_end();
bool allConstantOffsets = true;
// The first index of every GEP must be an array index.
assert((*firstIdx)->getType() == Type::LongTy &&
"INTERNAL ERROR: Structure index for a pointer type!");
// If the last instruction had a leading non-zero index, check if the
// current one references a sequential (i.e., indexable) type.
// If not, the code is not type-safe and we would create an illegal GEP
// by folding them, so don't fold any more instructions.
//
if (lastInstHasLeadingNonZero)
if (! isa<SequentialType>(gepInst->getType()->getElementType()))
break; // cannot fold in any preceding getElementPtr instrs.
// Check that all offsets are constant for this instruction
for (OI = firstIdx; allConstantOffsets && OI != lastIdx; ++OI)
allConstantOffsets = isa<ConstantInt>(*OI);
if (allConstantOffsets)
{ // Get pointer value out of ptrChild.
ptrVal = gepInst->getPointerOperand();
// Remember if it has leading zero index: it will be discarded later.
lastInstHasLeadingNonZero = ! IsZero(*firstIdx);
// Insert its index vector at the start, skipping any leading [0]
chainIdxVec.insert(chainIdxVec.begin(),
firstIdx + !lastInstHasLeadingNonZero, lastIdx);
// Mark the folded node so no code is generated for it.
((InstructionNode*) ptrChild)->markFoldedIntoParent();
// Get the previous GEP instruction and continue trying to fold
ptrChild = dyn_cast<InstructionNode>(ptrChild->leftChild());
}
else // cannot fold this getElementPtr instr. or any preceding ones
break;
}
// If the first getElementPtr instruction had a leading [0], add it back.
// Note that this instruction is the *last* one successfully folded above.
if (ptrVal && ! lastInstHasLeadingNonZero)
chainIdxVec.insert(chainIdxVec.begin(), ConstantSInt::get(Type::LongTy,0));
return ptrVal;
}
//---------------------------------------------------------------------------
// Function: GetGEPInstArgs
//
// Purpose:
// Helper function for GetMemInstArgs that handles the final getElementPtr
// instruction used by (or same as) the memory operation.
// Extracts the indices of the current instruction and tries to fold in
// preceding ones if all indices of the current one are constant.
//---------------------------------------------------------------------------
Value*
GetGEPInstArgs(InstructionNode* gepNode,
vector<Value*>& idxVec,
bool& allConstantIndices)
{
allConstantIndices = true;
GetElementPtrInst* gepI = cast<GetElementPtrInst>(gepNode->getInstruction());
// Default pointer is the one from the current instruction.
Value* ptrVal = gepI->getPointerOperand();
InstrTreeNode* ptrChild = gepNode->leftChild();
// Extract the index vector of the GEP instructin.
// If all indices are constant and first index is zero, try to fold
// in preceding GEPs with all constant indices.
for (User::op_iterator OI=gepI->idx_begin(), OE=gepI->idx_end();
allConstantIndices && OI != OE; ++OI)
if (! isa<Constant>(*OI))
allConstantIndices = false; // note: this also terminates loop!
// If we have only constant indices, fold chains of constant indices
// in this and any preceding GetElemPtr instructions.
bool foldedGEPs = false;
bool leadingNonZeroIdx = gepI && ! IsZero(*gepI->idx_begin());
if (allConstantIndices)
if (Value* newPtr = FoldGetElemChain(ptrChild, idxVec, leadingNonZeroIdx))
{
ptrVal = newPtr;
foldedGEPs = true;
}
// Append the index vector of the current instruction.
// Skip the leading [0] index if preceding GEPs were folded into this.
idxVec.insert(idxVec.end(),
gepI->idx_begin() + (foldedGEPs && !leadingNonZeroIdx),
gepI->idx_end());
return ptrVal;
}
//---------------------------------------------------------------------------
// Function: GetMemInstArgs
//
// Purpose:
// Get the pointer value and the index vector for a memory operation
// (GetElementPtr, Load, or Store). If all indices of the given memory
// operation are constant, fold in constant indices in a chain of
// preceding GetElementPtr instructions (if any), and return the
// pointer value of the first instruction in the chain.
// All folded instructions are marked so no code is generated for them.
//
// Return values:
// Returns the pointer Value to use.
// Returns the resulting IndexVector in idxVec.
// Returns true/false in allConstantIndices if all indices are/aren't const.
//---------------------------------------------------------------------------
Value*
GetMemInstArgs(InstructionNode* memInstrNode,
vector<Value*>& idxVec,
bool& allConstantIndices)
{
allConstantIndices = false;
Instruction* memInst = memInstrNode->getInstruction();
assert(idxVec.size() == 0 && "Need empty vector to return indices");
// If there is a GetElemPtr instruction to fold in to this instr,
// it must be in the left child for Load and GetElemPtr, and in the
// right child for Store instructions.
InstrTreeNode* ptrChild = (memInst->getOpcode() == Instruction::Store
? memInstrNode->rightChild()
: memInstrNode->leftChild());
// Default pointer is the one from the current instruction.
Value* ptrVal = ptrChild->getValue();
// Find the "last" GetElemPtr instruction: this one or the immediate child.
// There will be none if this is a load or a store from a scalar pointer.
InstructionNode* gepNode = NULL;
if (isa<GetElementPtrInst>(memInst))
gepNode = memInstrNode;
else if (isa<InstructionNode>(ptrChild) && isa<GetElementPtrInst>(ptrVal))
{ // Child of load/store is a GEP and memInst is its only use.
// Use its indices and mark it as folded.
gepNode = cast<InstructionNode>(ptrChild);
gepNode->markFoldedIntoParent();
}
// If there are no indices, return the current pointer.
// Else extract the pointer from the GEP and fold the indices.
return (gepNode)? GetGEPInstArgs(gepNode, idxVec, allConstantIndices)
: ptrVal;
}
//------------------------------------------------------------------------
// Function Set2OperandsFromInstr
// Function Set3OperandsFromInstr
//
// For the common case of 2- and 3-operand arithmetic/logical instructions,
// set the m/c instr. operands directly from the VM instruction's operands.
// Check whether the first or second operand is 0 and can use a dedicated "0"
// register.
// Check whether the second operand should use an immediate field or register.
// (First and third operands are never immediates for such instructions.)
//
// Arguments:
// canDiscardResult: Specifies that the result operand can be discarded
// by using the dedicated "0"
//
// op1position, op2position and resultPosition: Specify in which position
// in the machine instruction the 3 operands (arg1, arg2
// and result) should go.
//
//------------------------------------------------------------------------
void
Set2OperandsFromInstr(MachineInstr* minstr,
InstructionNode* vmInstrNode,
const TargetMachine& target,
bool canDiscardResult,
int op1Position,
int resultPosition)
{
Set3OperandsFromInstr(minstr, vmInstrNode, target,
canDiscardResult, op1Position,
/*op2Position*/ -1, resultPosition);
}
void
Set3OperandsFromInstr(MachineInstr* minstr,
InstructionNode* vmInstrNode,
const TargetMachine& target,
bool canDiscardResult,
int op1Position,
int op2Position,
int resultPosition)
{
assert(op1Position >= 0);
assert(resultPosition >= 0);
// operand 1
minstr->SetMachineOperandVal(op1Position, MachineOperand::MO_VirtualRegister,
vmInstrNode->leftChild()->getValue());
// operand 2 (if any)
if (op2Position >= 0)
minstr->SetMachineOperandVal(op2Position, MachineOperand::MO_VirtualRegister,
vmInstrNode->rightChild()->getValue());
// result operand: if it can be discarded, use a dead register if one exists
if (canDiscardResult && target.getRegInfo().getZeroRegNum() >= 0)
minstr->SetMachineOperandReg(resultPosition,
target.getRegInfo().getZeroRegNum());
else
minstr->SetMachineOperandVal(resultPosition,
MachineOperand::MO_VirtualRegister, vmInstrNode->getValue());
}
MachineOperand::MachineOperandType
ChooseRegOrImmed(int64_t intValue,
bool isSigned,
MachineOpCode opCode,
const TargetMachine& target,
bool canUseImmed,
unsigned int& getMachineRegNum,
int64_t& getImmedValue)
{
MachineOperand::MachineOperandType opType=MachineOperand::MO_VirtualRegister;
getMachineRegNum = 0;
getImmedValue = 0;
if (canUseImmed &&
target.getInstrInfo().constantFitsInImmedField(opCode, intValue))
{
opType = isSigned? MachineOperand::MO_SignExtendedImmed
: MachineOperand::MO_UnextendedImmed;
getImmedValue = intValue;
}
else if (intValue == 0 && target.getRegInfo().getZeroRegNum() >= 0)
{
opType = MachineOperand::MO_MachineRegister;
getMachineRegNum = target.getRegInfo().getZeroRegNum();
}
return opType;
}
MachineOperand::MachineOperandType
ChooseRegOrImmed(Value* val,
MachineOpCode opCode,
const TargetMachine& target,
bool canUseImmed,
unsigned int& getMachineRegNum,
int64_t& getImmedValue)
{
getMachineRegNum = 0;
getImmedValue = 0;
// To use reg or immed, constant needs to be integer, bool, or a NULL pointer
Constant *CPV = dyn_cast<Constant>(val);
if (CPV == NULL ||
(! CPV->getType()->isIntegral() &&
! (isa<PointerType>(CPV->getType()) && CPV->isNullValue())))
return MachineOperand::MO_VirtualRegister;
// Now get the constant value and check if it fits in the IMMED field.
// Take advantage of the fact that the max unsigned value will rarely
// fit into any IMMED field and ignore that case (i.e., cast smaller
// unsigned constants to signed).
//
int64_t intValue;
if (isa<PointerType>(CPV->getType()))
intValue = 0; // We checked above that it is NULL
else if (ConstantBool* CB = dyn_cast<ConstantBool>(CPV))
intValue = (int64_t) CB->getValue();
else if (CPV->getType()->isSigned())
intValue = cast<ConstantSInt>(CPV)->getValue();
else
{ // get the int value and sign-extend if original was less than 64 bits
intValue = (int64_t) cast<ConstantUInt>(CPV)->getValue();
switch(CPV->getType()->getPrimitiveID())
{
case Type::UByteTyID: intValue = (int64_t) (int8_t) intValue; break;
case Type::UShortTyID: intValue = (int64_t) (short) intValue; break;
case Type::UIntTyID: intValue = (int64_t) (int) intValue; break;
default: break;
}
}
return ChooseRegOrImmed(intValue, CPV->getType()->isSigned(),
opCode, target, canUseImmed,
getMachineRegNum, getImmedValue);
}
//---------------------------------------------------------------------------
// Function: FixConstantOperandsForInstr
//
// Purpose:
// Special handling for constant operands of a machine instruction
// -- if the constant is 0, use the hardwired 0 register, if any;
// -- if the constant fits in the IMMEDIATE field, use that field;
// -- else create instructions to put the constant into a register, either
// directly or by loading explicitly from the constant pool.
//
// In the first 2 cases, the operand of `minstr' is modified in place.
// Returns a vector of machine instructions generated for operands that
// fall under case 3; these must be inserted before `minstr'.
//---------------------------------------------------------------------------
vector<MachineInstr*>
FixConstantOperandsForInstr(Instruction* vmInstr,
MachineInstr* minstr,
TargetMachine& target)
{
vector<MachineInstr*> loadConstVec;
MachineOpCode opCode = minstr->getOpCode();
const MachineInstrInfo& instrInfo = target.getInstrInfo();
const MachineInstrDescriptor& instrDesc = instrInfo.getDescriptor(opCode);
int immedPos = instrInfo.getImmedConstantPos(opCode);
Function *F = vmInstr->getParent()->getParent();
for (unsigned op=0; op < minstr->getNumOperands(); op++)
{
const MachineOperand& mop = minstr->getOperand(op);
// Skip the result position, preallocated machine registers, or operands
// that cannot be constants (CC regs or PC-relative displacements)
if (instrDesc.resultPos == (int) op ||
mop.getOperandType() == MachineOperand::MO_MachineRegister ||
mop.getOperandType() == MachineOperand::MO_CCRegister ||
mop.getOperandType() == MachineOperand::MO_PCRelativeDisp)
continue;
bool constantThatMustBeLoaded = false;
unsigned int machineRegNum = 0;
int64_t immedValue = 0;
Value* opValue = NULL;
MachineOperand::MachineOperandType opType =
MachineOperand::MO_VirtualRegister;
// Operand may be a virtual register or a compile-time constant
if (mop.getOperandType() == MachineOperand::MO_VirtualRegister)
{
assert(mop.getVRegValue() != NULL);
opValue = mop.getVRegValue();
if (Constant *opConst = dyn_cast<Constant>(opValue))
{
opType = ChooseRegOrImmed(opConst, opCode, target,
(immedPos == (int)op), machineRegNum, immedValue);
if (opType == MachineOperand::MO_VirtualRegister)
constantThatMustBeLoaded = true;
}
}
else
{
assert(mop.getOperandType() == MachineOperand::MO_SignExtendedImmed ||
mop.getOperandType() == MachineOperand::MO_UnextendedImmed);
bool isSigned = (mop.getOperandType() ==
MachineOperand::MO_SignExtendedImmed);
// Bit-selection flags indicate an instruction that is extracting
// bits from its operand so ignore this even if it is a big constant.
if (mop.opHiBits32() || mop.opLoBits32() ||
mop.opHiBits64() || mop.opLoBits64())
continue;
opType = ChooseRegOrImmed(mop.getImmedValue(), isSigned,
opCode, target, (immedPos == (int)op),
machineRegNum, immedValue);
if (opType == mop.getOperandType())
continue; // no change: this is the most common case
if (opType == MachineOperand::MO_VirtualRegister)
{
constantThatMustBeLoaded = true;
opValue = isSigned
? (Value*)ConstantSInt::get(Type::LongTy, immedValue)
: (Value*)ConstantUInt::get(Type::ULongTy,(uint64_t)immedValue);
}
}
if (opType == MachineOperand::MO_MachineRegister)
minstr->SetMachineOperandReg(op, machineRegNum);
else if (opType == MachineOperand::MO_SignExtendedImmed ||
opType == MachineOperand::MO_UnextendedImmed)
minstr->SetMachineOperandConst(op, opType, immedValue);
else if (constantThatMustBeLoaded ||
(opValue && isa<GlobalValue>(opValue)))
{ // opValue is a constant that must be explicitly loaded into a reg
assert(opValue);
TmpInstruction* tmpReg = InsertCodeToLoadConstant(F, opValue, vmInstr,
loadConstVec, target);
minstr->SetMachineOperandVal(op, MachineOperand::MO_VirtualRegister,
tmpReg);
}
}
// Also, check for implicit operands used by the machine instruction
// (no need to check those defined since they cannot be constants).
// These include:
// -- arguments to a Call
// -- return value of a Return
// Any such operand that is a constant value needs to be fixed also.
// The current instructions with implicit refs (viz., Call and Return)
// have no immediate fields, so the constant always needs to be loaded
// into a register.
//
bool isCall = instrInfo.isCall(opCode);
unsigned lastCallArgNum = 0; // unused if not a call
CallArgsDescriptor* argDesc = NULL; // unused if not a call
if (isCall)
argDesc = CallArgsDescriptor::get(minstr);
for (unsigned i=0, N=minstr->getNumImplicitRefs(); i < N; ++i)
if (isa<Constant>(minstr->getImplicitRef(i)) ||
isa<GlobalValue>(minstr->getImplicitRef(i)))
{
Value* oldVal = minstr->getImplicitRef(i);
TmpInstruction* tmpReg =
InsertCodeToLoadConstant(F, oldVal, vmInstr, loadConstVec, target);
minstr->setImplicitRef(i, tmpReg);
if (isCall)
{ // find and replace the argument in the CallArgsDescriptor
unsigned i=lastCallArgNum;
while (argDesc->getArgInfo(i).getArgVal() != oldVal)
++i;
assert(i < argDesc->getNumArgs() &&
"Constant operands to a call *must* be in the arg list");
lastCallArgNum = i;
argDesc->getArgInfo(i).replaceArgVal(tmpReg);
}
}
return loadConstVec;
}
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