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For 16 and 32-bit multiplies, use the IMUL instruction instead of the MUL instruction. 

This allows us to not force the use of the EAX/AX registers!

llvm-svn: 6830
This commit is contained in:
Chris Lattner 2003-06-21 17:16:58 +00:00
parent 2a67e0cf02
commit 22f54501be
1 changed files with 11 additions and 21 deletions
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32
llvm/lib/Target/X86/InstSelectSimple.cpp
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@ -1069,8 +1069,6 @@ void ISel::emitSimpleBinaryOperation(MachineBasicBlock *BB,
/// registers op0Reg and op1Reg, and put the result in DestReg. The type of the
/// result should be given as DestTy.
///
/// FIXME: doMultiply should use one of the two address IMUL instructions!
///
void ISel::doMultiply(MachineBasicBlock *MBB, MachineBasicBlock::iterator &MBBI,
unsigned DestReg, const Type *DestTy,
unsigned op0Reg, unsigned op1Reg) {
@ -1079,28 +1077,20 @@ void ISel::doMultiply(MachineBasicBlock *MBB, MachineBasicBlock::iterator &MBBI,
case cFP: // Floating point multiply
BMI(BB, MBBI, X86::FpMUL, 2, DestReg).addReg(op0Reg).addReg(op1Reg);
return;
case cInt:
case cShort:
BMI(BB, MBBI, Class == cInt ? X86::IMULr32 : X86::IMULr16, 2, DestReg)
.addReg(op0Reg).addReg(op1Reg);
return;
case cByte:
// Must use the MUL instruction, which forces use of AL...
BMI(MBB, MBBI, X86::MOVrr8, 1, X86::AL).addReg(op0Reg);
BMI(MBB, MBBI, X86::MULr8, 1).addReg(op1Reg);
BMI(MBB, MBBI, X86::MOVrr8, 1, DestReg).addReg(X86::AL);
return;
default:
case cLong: assert(0 && "doMultiply cannot operate on LONG values!");
case cByte:
case cShort:
case cInt: // Small integerals, handled below...
break;
}
static const unsigned Regs[] ={ X86::AL , X86::AX , X86::EAX };
static const unsigned MulOpcode[]={ X86::MULr8 , X86::MULr16 , X86::MULr32 };
static const unsigned MovOpcode[]={ X86::MOVrr8, X86::MOVrr16, X86::MOVrr32 };
unsigned Reg = Regs[Class];
// Emit a MOV to put the first operand into the appropriately-sized
// subreg of EAX.
BMI(MBB, MBBI, MovOpcode[Class], 1, Reg).addReg(op0Reg);
// Emit the appropriate multiply instruction.
BMI(MBB, MBBI, MulOpcode[Class], 1).addReg(op1Reg);
// Emit another MOV to put the result into the destination register.
BMI(MBB, MBBI, MovOpcode[Class], 1, DestReg).addReg(Reg);
}
/// visitMul - Multiplies are not simple binary operators because they must deal