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Add some comments about REX fields 

llvm-svn: 105860
This commit is contained in:
Bruno Cardoso Lopes 2010-06-12 00:03:52 +00:00
parent fd5458d4bd
commit 8947c32493
1 changed files with 10 additions and 10 deletions
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20
llvm/lib/Target/X86/X86MCCodeEmitter.cpp
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@ -502,7 +502,7 @@ static unsigned DetermineREXPrefix(const MCInst &MI, uint64_t TSFlags,
unsigned REX = 0;
if (TSFlags & X86II::REX_W)
REX |= 1 << 3;
REX |= 1 << 3; // set REX.W
if (MI.getNumOperands() == 0) return REX;
@ -520,7 +520,7 @@ static unsigned DetermineREXPrefix(const MCInst &MI, uint64_t TSFlags,
if (!X86InstrInfo::isX86_64NonExtLowByteReg(Reg)) continue;
// FIXME: The caller of DetermineREXPrefix slaps this prefix onto anything
// that returns non-zero.
REX |= 0x40;
REX |= 0x40; // REX fixed encoding prefix
break;
}
@ -529,25 +529,25 @@ static unsigned DetermineREXPrefix(const MCInst &MI, uint64_t TSFlags,
case X86II::MRMSrcReg:
if (MI.getOperand(0).isReg() &&
X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(0).getReg()))
REX |= 1 << 2;
REX |= 1 << 2; // set REX.R
i = isTwoAddr ? 2 : 1;
for (; i != NumOps; ++i) {
const MCOperand &MO = MI.getOperand(i);
if (MO.isReg() && X86InstrInfo::isX86_64ExtendedReg(MO.getReg()))
REX |= 1 << 0;
REX |= 1 << 0; // set REX.B
}
break;
case X86II::MRMSrcMem: {
if (MI.getOperand(0).isReg() &&
X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(0).getReg()))
REX |= 1 << 2;
REX |= 1 << 2; // set REX.R
unsigned Bit = 0;
i = isTwoAddr ? 2 : 1;
for (; i != NumOps; ++i) {
const MCOperand &MO = MI.getOperand(i);
if (MO.isReg()) {
if (X86InstrInfo::isX86_64ExtendedReg(MO.getReg()))
REX |= 1 << Bit;
REX |= 1 << Bit; // set REX.B (Bit=0) and REX.X (Bit=1)
Bit++;
}
}
@ -562,13 +562,13 @@ static unsigned DetermineREXPrefix(const MCInst &MI, uint64_t TSFlags,
i = isTwoAddr ? 1 : 0;
if (NumOps > e && MI.getOperand(e).isReg() &&
X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(e).getReg()))
REX |= 1 << 2;
REX |= 1 << 2; // set REX.R
unsigned Bit = 0;
for (; i != e; ++i) {
const MCOperand &MO = MI.getOperand(i);
if (MO.isReg()) {
if (X86InstrInfo::isX86_64ExtendedReg(MO.getReg()))
REX |= 1 << Bit;
REX |= 1 << Bit; // REX.B (Bit=0) and REX.X (Bit=1)
Bit++;
}
}
@ -577,12 +577,12 @@ static unsigned DetermineREXPrefix(const MCInst &MI, uint64_t TSFlags,
default:
if (MI.getOperand(0).isReg() &&
X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(0).getReg()))
REX |= 1 << 0;
REX |= 1 << 0; // set REX.B
i = isTwoAddr ? 2 : 1;
for (unsigned e = NumOps; i != e; ++i) {
const MCOperand &MO = MI.getOperand(i);
if (MO.isReg() && X86InstrInfo::isX86_64ExtendedReg(MO.getReg()))
REX |= 1 << 2;
REX |= 1 << 2; // set REX.R
}
break;
}