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Simplify code by using the more powerful BuildMI forms.

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Implement a small optimization.  In test/Regression/CodeGen/X86/select.ll,
we now generate this for foldSel3:

foldSel3:
        mov %AL, BYTE PTR [%ESP + 4]
        fld DWORD PTR [%ESP + 8]
        fld DWORD PTR [%ESP + 12]
        mov %EAX, DWORD PTR [%ESP + 16]
        mov %ECX, DWORD PTR [%ESP + 20]
        cmp %EAX, %ECX
        fxch %ST(1)
        fcmovae %ST(0), %ST(1)
***     fstp %ST(1)
        ret

Instead of:

foldSel3:
        mov %AL, BYTE PTR [%ESP + 4]
        fld DWORD PTR [%ESP + 8]
        fld DWORD PTR [%ESP + 12]
        mov %EAX, DWORD PTR [%ESP + 16]
        mov %ECX, DWORD PTR [%ESP + 20]
        cmp %EAX, %ECX
        fxch %ST(1)
        fcmovae %ST(0), %ST(1)
***     fxch %ST(1)
***     fstp %ST(0)
        ret

In practice, this only effects code size: performance should be basically
unaffected.

llvm-svn: 12588
This commit is contained in:
Chris Lattner 2004-04-01 04:06:09 +00:00
parent 78027ca4ff
commit b6e4e5a95e
1 changed files with 41 additions and 34 deletions
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75
lib/Target/X86/FloatingPoint.cpp
View File

@ -118,25 +118,29 @@ namespace {
std::swap(Stack[RegMap[RegOnTop]], Stack[StackTop-1]);
// Emit an fxch to update the runtime processors version of the state
MachineInstr *MI = BuildMI(X86::FXCH, 1).addReg(STReg);
MBB->insert(I, MI);
BuildMI(*MBB, I, X86::FXCH, 1).addReg(STReg);
NumFXCH++;
}
}
void duplicateToTop(unsigned RegNo, unsigned AsReg,
MachineBasicBlock::iterator &I) {
void duplicateToTop(unsigned RegNo, unsigned AsReg, MachineInstr *I) {
unsigned STReg = getSTReg(RegNo);
pushReg(AsReg); // New register on top of stack
MachineInstr *MI = BuildMI(X86::FLDrr, 1).addReg(STReg);
MBB->insert(I, MI);
BuildMI(*MBB, I, X86::FLDrr, 1).addReg(STReg);
}
// popStackAfter - Pop the current value off of the top of the FP stack
// after the specified instruction.
void popStackAfter(MachineBasicBlock::iterator &I);
// freeStackSlotAfter - Free the specified register from the register stack,
// so that it is no longer in a register. If the register is currently at
// the top of the stack, we just pop the current instruction, otherwise we
// store the current top-of-stack into the specified slot, then pop the top
// of stack.
void freeStackSlotAfter(MachineBasicBlock::iterator &I, unsigned Reg);
bool processBasicBlock(MachineFunction &MF, MachineBasicBlock &MBB);
void handleZeroArgFP(MachineBasicBlock::iterator &I);
@ -250,7 +254,7 @@ bool FPS::processBasicBlock(MachineFunction &MF, MachineBasicBlock &BB) {
DEBUG(
MachineBasicBlock::iterator PrevI(PrevMI);
if (I == PrevI) {
std::cerr<< "Just deleted pseudo instruction\n";
std::cerr << "Just deleted pseudo instruction\n";
} else {
MachineBasicBlock::iterator Start = I;
// Rewind to first instruction newly inserted.
@ -358,11 +362,34 @@ void FPS::popStackAfter(MachineBasicBlock::iterator &I) {
I->RemoveOperand(0);
} else { // Insert an explicit pop
MachineInstr *MI = BuildMI(X86::FSTPrr, 1).addReg(X86::ST0);
I = MBB->insert(++I, MI);
I = BuildMI(*MBB, ++I, X86::FSTPrr, 1).addReg(X86::ST0);
}
}
/// freeStackSlotAfter - Free the specified register from the register stack, so
/// that it is no longer in a register. If the register is currently at the top
/// of the stack, we just pop the current instruction, otherwise we store the
/// current top-of-stack into the specified slot, then pop the top of stack.
void FPS::freeStackSlotAfter(MachineBasicBlock::iterator &I, unsigned FPRegNo) {
if (getStackEntry(0) == FPRegNo) { // already at the top of stack? easy.
popStackAfter(I);
return;
}
// Otherwise, store the top of stack into the dead slot, killing the operand
// without having to add in an explicit xchg then pop.
//
unsigned STReg = getSTReg(FPRegNo);
unsigned OldSlot = getSlot(FPRegNo);
unsigned TopReg = Stack[StackTop-1];
Stack[OldSlot] = TopReg;
RegMap[TopReg] = OldSlot;
RegMap[FPRegNo] = ~0;
Stack[--StackTop] = ~0;
I = BuildMI(*MBB, ++I, X86::FSTPrr, 1).addReg(STReg);
}
static unsigned getFPReg(const MachineOperand &MO) {
assert(MO.isRegister() && "Expected an FP register!");
unsigned Reg = MO.getReg();
@ -596,8 +623,7 @@ void FPS::handleTwoArgFP(MachineBasicBlock::iterator &I) {
// Replace the old instruction with a new instruction
MBB->remove(I++);
BuildMI(*MBB, I, Opcode, 1).addReg(getSTReg(NotTOS));
--I;
I = BuildMI(*MBB, I, Opcode, 1).addReg(getSTReg(NotTOS));
// If both operands are killed, pop one off of the stack in addition to
// overwriting the other one.
@ -610,25 +636,8 @@ void FPS::handleTwoArgFP(MachineBasicBlock::iterator &I) {
if (MI->getOpcode() == X86::FpUCOM) {
if (KillsOp0 && !KillsOp1)
popStackAfter(I); // If we kill the first operand, pop it!
else if (KillsOp1 && Op0 != Op1) {
if (getStackEntry(0) == Op1) {
popStackAfter(I); // If it's right at the top of stack, just pop it
} else {
// Otherwise, move the top of stack into the dead slot, killing the
// operand without having to add in an explicit xchg then pop.
//
unsigned STReg = getSTReg(Op1);
unsigned OldSlot = getSlot(Op1);
unsigned TopReg = Stack[StackTop-1];
Stack[OldSlot] = TopReg;
RegMap[TopReg] = OldSlot;
RegMap[Op1] = ~0;
Stack[--StackTop] = ~0;
MachineInstr *MI = BuildMI(X86::FSTPrr, 1).addReg(STReg);
I = MBB->insert(++I, MI);
}
}
else if (KillsOp1 && Op0 != Op1)
freeStackSlotAfter(I, Op1);
}
// Update stack information so that we know the destination register is now on
@ -663,10 +672,8 @@ void FPS::handleCondMovFP(MachineBasicBlock::iterator &I) {
for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
E = LV->killed_end(MI); KI != E; ++KI)
if (KI->second == X86::FP0+Op1) {
++I;
moveToTop(Op1, I); // Insert fxch if necessary
--I;
popStackAfter(I); // Pop the top of the stack, killing value
// Get this value off of the register stack.
freeStackSlotAfter(I, Op1);
break;
}
}