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This optimization greatly enhances efficiency of creating new instructions by 

masking and shifting operands directly into their place in the instruction,
instead of the old-fashioned way of ORing in each bit separately.

llvm-svn: 7179
This commit is contained in:
Misha Brukman 2003-07-15 21:00:32 +00:00
parent 384cb5dd10
commit 1912eaf0a0
1 changed files with 106 additions and 6 deletions
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108
llvm/support/tools/TableGen/CodeEmitterGen.cpp
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@ -59,6 +59,7 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
//
unsigned op = 0;
std::map<const std::string,unsigned> OpOrder;
std::map<const std::string,bool> OpContinuous;
for (unsigned i = 0, e = Vals.size(); i != e; ++i) {
if (Vals[i].getName() != "Inst" &&
!Vals[i].getValue()->isComplete() &&
@ -71,6 +72,90 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
<<" = getMachineOpValue(MI, MI.getOperand("<<op<<"));\n";
//<< " MachineOperand &op" << op <<" = MI.getOperand("<<op<<");\n";
OpOrder[Vals[i].getName()] = op++;
// Is the operand continuous? If so, we can just mask and OR it in
// instead of doing it bit-by-bit, saving a lot in runtime cost.
const BitsInit *InstInit = BI;
int beginBitInVar = -1, endBitInVar = -1,
beginBitInInst = -1, endBitInInst = -1;
bool continuous = true;
for (int bit = InstInit->getNumBits()-1; bit >= 0; --bit) {
if (VarBitInit *VBI =
dynamic_cast<VarBitInit*>(InstInit->getBit(bit))) {
TypedInit *TI = VBI->getVariable();
if (VarInit *VI = dynamic_cast<VarInit*>(TI)) {
// only process the current variable
if (VI->getName() != Vals[i].getName())
continue;
if (beginBitInVar == -1)
beginBitInVar = VBI->getBitNum();
if (endBitInVar == -1)
endBitInVar = VBI->getBitNum();
else {
if (endBitInVar == (int)VBI->getBitNum() + 1)
endBitInVar = VBI->getBitNum();
else {
continuous = false;
break;
}
}
if (beginBitInInst == -1)
beginBitInInst = bit;
if (endBitInInst == -1)
endBitInInst = bit;
else {
if (endBitInInst == bit + 1)
endBitInInst = bit;
else {
continuous = false;
break;
}
}
// maintain same distance between bits in field and bits in
// instruction. if the relative distances stay the same
// throughout,
if ((beginBitInVar - (int)VBI->getBitNum()) !=
(beginBitInInst - bit))
{
continuous = false;
break;
}
}
}
}
if (continuous) {
o << " // continuous: op" << OpOrder[Vals[i].getName()] << "\n";
// Mask off the right bits
// Low mask (ie. shift, if necessary)
if (endBitInVar != 0) {
o << " op" << OpOrder[Vals[i].getName()]
<< " >>= endBitInVar;\n";
beginBitInVar -= endBitInVar;
endBitInVar = 0;
}
// High mask
o << " op" << OpOrder[Vals[i].getName()]
<< " &= (1<<" << beginBitInVar+1 << ") - 1;\n";
// Shift the value to the correct place (according to place in instr)
if (endBitInInst != 0)
o << " op" << OpOrder[Vals[i].getName()]
<< " <<= " << endBitInInst << ";\n";
// Just OR in the result
o << " Value |= op" << OpOrder[Vals[i].getName()] << ";\n";
}
// otherwise, will be taken care of in the loop below using this value:
OpContinuous[Vals[i].getName()] = continuous;
}
}
@ -81,7 +166,8 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
// Scan through the field looking for bit initializers of the current
// variable...
for (int i = FieldInitializer->getNumBits()-1; i >= 0; --i) {
if (BitInit *BI=dynamic_cast<BitInit*>(FieldInitializer->getBit(i))){
if (BitInit *BI=dynamic_cast<BitInit*>(FieldInitializer->getBit(i)))
{
o << " // bit init: f: " << f << ", i: " << i << "\n";
} else if (UnsetInit *UI =
dynamic_cast<UnsetInit*>(FieldInitializer->getBit(i))) {
@ -90,9 +176,22 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
dynamic_cast<VarBitInit*>(FieldInitializer->getBit(i))) {
TypedInit *TI = VBI->getVariable();
if (VarInit *VI = dynamic_cast<VarInit*>(TI)) {
o << " Value |= getValueBit(op" << OpOrder[VI->getName()]
<< ", " << VBI->getBitNum()
<< ")" << " << " << i << ";\n";
// If the bits of the field are laid out consecutively in the
// instruction, then instead of separately ORing in bits, just
// mask and shift the entire field for efficiency.
if (OpContinuous[VI->getName()]) {
// already taken care of in the loop above, thus there is no
// need to individually OR in the bits
// for debugging, output the regular version anyway, commented
o << " // Value |= getValueBit(op"
<< OpOrder[VI->getName()] << ", " << VBI->getBitNum()
<< ")" << " << " << i << ";\n";
} else {
o << " Value |= getValueBit(op" << OpOrder[VI->getName()]
<< ", " << VBI->getBitNum()
<< ")" << " << " << i << ";\n";
}
} else if (FieldInit *FI = dynamic_cast<FieldInit*>(TI)) {
// FIXME: implement this!
o << "FIELD INIT not implemented yet!\n";
@ -112,6 +211,7 @@ void CodeEmitterGen::createEmitter(std::ostream &o) {
o << " break;\n"
<< " }\n";
}
o << " default:\n"
<< " DEBUG(std::cerr << \"Not supported instr: \" << MI << \"\\n\");\n"
<< " abort();\n"