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llvm/lib/Target/X86/X86FloatingPoint.cpp
Misha Brukman 5560c9d49c Spell `necessary' correctly. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7944 91177308-0d34-0410-b5e6-96231b3b80d8
2003-08-18 14:43:39 +00:00

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//===-- FloatingPoint.cpp - Floating point Reg -> Stack converter ---------===//
//
// This file defines the pass which converts floating point instructions from
// virtual registers into register stack instructions.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "fp"
#include "X86.h"
#include "X86InstrInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include <algorithm>
#include <iostream>
namespace {
Statistic<> NumFXCH("x86-codegen", "Number of fxch instructions inserted");
Statistic<> NumFP ("x86-codegen", "Number of floating point instructions");
struct FPS : public MachineFunctionPass {
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "X86 FP Stackifier"; }
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveVariables>();
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
LiveVariables *LV; // Live variable info for current function...
MachineBasicBlock *MBB; // Current basic block
unsigned Stack[8]; // FP<n> Registers in each stack slot...
unsigned RegMap[8]; // Track which stack slot contains each register
unsigned StackTop; // The current top of the FP stack.
void dumpStack() const {
std::cerr << "Stack contents:";
for (unsigned i = 0; i != StackTop; ++i) {
std::cerr << " FP" << Stack[i];
assert(RegMap[Stack[i]] == i && "Stack[] doesn't match RegMap[]!");
}
std::cerr << "\n";
}
private:
// getSlot - Return the stack slot number a particular register number is
// in...
unsigned getSlot(unsigned RegNo) const {
assert(RegNo < 8 && "Regno out of range!");
return RegMap[RegNo];
}
// getStackEntry - Return the X86::FP<n> register in register ST(i)
unsigned getStackEntry(unsigned STi) const {
assert(STi < StackTop && "Access past stack top!");
return Stack[StackTop-1-STi];
}
// getSTReg - Return the X86::ST(i) register which contains the specified
// FP<RegNo> register
unsigned getSTReg(unsigned RegNo) const {
return StackTop - 1 - getSlot(RegNo) + X86::ST0;
}
// pushReg - Push the specifiex FP<n> register onto the stack
void pushReg(unsigned Reg) {
assert(Reg < 8 && "Register number out of range!");
assert(StackTop < 8 && "Stack overflow!");
Stack[StackTop] = Reg;
RegMap[Reg] = StackTop++;
}
bool isAtTop(unsigned RegNo) const { return getSlot(RegNo) == StackTop-1; }
void moveToTop(unsigned RegNo, MachineBasicBlock::iterator &I) {
if (!isAtTop(RegNo)) {
unsigned Slot = getSlot(RegNo);
unsigned STReg = getSTReg(RegNo);
unsigned RegOnTop = getStackEntry(0);
// Swap the slots the regs are in
std::swap(RegMap[RegNo], RegMap[RegOnTop]);
// Swap stack slot contents
assert(RegMap[RegOnTop] < StackTop);
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);
I = 1+MBB->insert(I, MI);
NumFXCH++;
}
}
void duplicateToTop(unsigned RegNo, unsigned AsReg,
MachineBasicBlock::iterator &I) {
unsigned STReg = getSTReg(RegNo);
pushReg(AsReg); // New register on top of stack
MachineInstr *MI = BuildMI(X86::FLDrr, 1).addReg(STReg);
I = 1+MBB->insert(I, MI);
}
// popStackAfter - Pop the current value off of the top of the FP stack
// after the specified instruction.
void popStackAfter(MachineBasicBlock::iterator &I);
bool processBasicBlock(MachineFunction &MF, MachineBasicBlock &MBB);
void handleZeroArgFP(MachineBasicBlock::iterator &I);
void handleOneArgFP(MachineBasicBlock::iterator &I);
void handleTwoArgFP(MachineBasicBlock::iterator &I);
void handleSpecialFP(MachineBasicBlock::iterator &I);
};
}
FunctionPass *createX86FloatingPointStackifierPass() { return new FPS(); }
/// runOnMachineFunction - Loop over all of the basic blocks, transforming FP
/// register references into FP stack references.
///
bool FPS::runOnMachineFunction(MachineFunction &MF) {
LV = &getAnalysis<LiveVariables>();
StackTop = 0;
bool Changed = false;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
Changed |= processBasicBlock(MF, *I);
return Changed;
}
/// processBasicBlock - Loop over all of the instructions in the basic block,
/// transforming FP instructions into their stack form.
///
bool FPS::processBasicBlock(MachineFunction &MF, MachineBasicBlock &BB) {
const TargetInstrInfo &TII = MF.getTarget().getInstrInfo();
bool Changed = false;
MBB = &BB;
for (MachineBasicBlock::iterator I = BB.begin(); I != BB.end(); ++I) {
MachineInstr *MI = *I;
MachineInstr *PrevMI = I == BB.begin() ? 0 : *(I-1);
unsigned Flags = TII.get(MI->getOpcode()).TSFlags;
if ((Flags & X86II::FPTypeMask) == 0) continue; // Ignore non-fp insts!
++NumFP; // Keep track of # of pseudo instrs
DEBUG(std::cerr << "\nFPInst:\t";
MI->print(std::cerr, MF.getTarget()));
// Get dead variables list now because the MI pointer may be deleted as part
// of processing!
LiveVariables::killed_iterator IB = LV->dead_begin(MI);
LiveVariables::killed_iterator IE = LV->dead_end(MI);
DEBUG(const MRegisterInfo *MRI = MF.getTarget().getRegisterInfo();
LiveVariables::killed_iterator I = LV->killed_begin(MI);
LiveVariables::killed_iterator E = LV->killed_end(MI);
if (I != E) {
std::cerr << "Killed Operands:";
for (; I != E; ++I)
std::cerr << " %" << MRI->getName(I->second);
std::cerr << "\n";
});
switch (Flags & X86II::FPTypeMask) {
case X86II::ZeroArgFP: handleZeroArgFP(I); break;
case X86II::OneArgFP: handleOneArgFP(I); break;
case X86II::OneArgFPRW: // ST(0) = fsqrt(ST(0))
assert(0 && "FP instr type not handled yet!");
case X86II::TwoArgFP: handleTwoArgFP(I); break;
case X86II::SpecialFP: handleSpecialFP(I); break;
default: assert(0 && "Unknown FP Type!");
}
// Check to see if any of the values defined by this instruction are dead
// after definition. If so, pop them.
for (; IB != IE; ++IB) {
unsigned Reg = IB->second;
if (Reg >= X86::FP0 && Reg <= X86::FP6) {
DEBUG(std::cerr << "Register FP#" << Reg-X86::FP0 << " is dead!\n");
++I; // Insert fxch AFTER the instruction
moveToTop(Reg-X86::FP0, I); // Insert fxch if necessary
--I; // Move to fxch or old instruction
popStackAfter(I); // Pop the top of the stack, killing value
}
}
// Print out all of the instructions expanded to if -debug
DEBUG(if (*I == PrevMI) {
std::cerr<< "Just deleted pseudo instruction\n";
} else {
MachineBasicBlock::iterator Start = I;
// Rewind to first instruction newly inserted.
while (Start != BB.begin() && *(Start-1) != PrevMI) --Start;
std::cerr << "Inserted instructions:\n\t";
(*Start)->print(std::cerr, MF.getTarget());
while (++Start != I+1);
}
dumpStack();
);
Changed = true;
}
assert(StackTop == 0 && "Stack not empty at end of basic block?");
return Changed;
}
//===----------------------------------------------------------------------===//
// Efficient Lookup Table Support
//===----------------------------------------------------------------------===//
struct TableEntry {
unsigned from;
unsigned to;
bool operator<(const TableEntry &TE) const { return from < TE.from; }
bool operator<(unsigned V) const { return from < V; }
};
static bool TableIsSorted(const TableEntry *Table, unsigned NumEntries) {
for (unsigned i = 0; i != NumEntries-1; ++i)
if (!(Table[i] < Table[i+1])) return false;
return true;
}
static int Lookup(const TableEntry *Table, unsigned N, unsigned Opcode) {
const TableEntry *I = std::lower_bound(Table, Table+N, Opcode);
if (I != Table+N && I->from == Opcode)
return I->to;
return -1;
}
#define ARRAY_SIZE(TABLE) \
(sizeof(TABLE)/sizeof(TABLE[0]))
#ifdef NDEBUG
#define ASSERT_SORTED(TABLE)
#else
#define ASSERT_SORTED(TABLE) \
{ static bool TABLE##Checked = false; \
if (!TABLE##Checked) \
assert(TableIsSorted(TABLE, ARRAY_SIZE(TABLE)) && \
"All lookup tables must be sorted for efficient access!"); \
}
#endif
//===----------------------------------------------------------------------===//
// Helper Methods
//===----------------------------------------------------------------------===//
// PopTable - Sorted map of instructions to their popping version. The first
// element is an instruction, the second is the version which pops.
//
static const TableEntry PopTable[] = {
{ X86::FADDrST0 , X86::FADDPrST0 },
{ X86::FDIVRrST0, X86::FDIVRPrST0 },
{ X86::FDIVrST0 , X86::FDIVPrST0 },
{ X86::FISTr16 , X86::FISTPr16 },
{ X86::FISTr32 , X86::FISTPr32 },
{ X86::FMULrST0 , X86::FMULPrST0 },
{ X86::FSTr32 , X86::FSTPr32 },
{ X86::FSTr64 , X86::FSTPr64 },
{ X86::FSTrr , X86::FSTPrr },
{ X86::FSUBRrST0, X86::FSUBRPrST0 },
{ X86::FSUBrST0 , X86::FSUBPrST0 },
{ X86::FUCOMPr , X86::FUCOMPPr },
{ X86::FUCOMr , X86::FUCOMPr },
};
/// popStackAfter - Pop the current value off of the top of the FP stack after
/// the specified instruction. This attempts to be sneaky and combine the pop
/// into the instruction itself if possible. The iterator is left pointing to
/// the last instruction, be it a new pop instruction inserted, or the old
/// instruction if it was modified in place.
///
void FPS::popStackAfter(MachineBasicBlock::iterator &I) {
ASSERT_SORTED(PopTable);
assert(StackTop > 0 && "Cannot pop empty stack!");
RegMap[Stack[--StackTop]] = ~0; // Update state
// Check to see if there is a popping version of this instruction...
int Opcode = Lookup(PopTable, ARRAY_SIZE(PopTable), (*I)->getOpcode());
if (Opcode != -1) {
(*I)->setOpcode(Opcode);
if (Opcode == X86::FUCOMPPr)
(*I)->RemoveOperand(0);
} else { // Insert an explicit pop
MachineInstr *MI = BuildMI(X86::FSTPrr, 1).addReg(X86::ST0);
I = MBB->insert(I+1, MI);
}
}
static unsigned getFPReg(const MachineOperand &MO) {
assert(MO.isPhysicalRegister() && "Expected an FP register!");
unsigned Reg = MO.getReg();
assert(Reg >= X86::FP0 && Reg <= X86::FP6 && "Expected FP register!");
return Reg - X86::FP0;
}
//===----------------------------------------------------------------------===//
// Instruction transformation implementation
//===----------------------------------------------------------------------===//
/// handleZeroArgFP - ST(0) = fld0 ST(0) = flds <mem>
//
void FPS::handleZeroArgFP(MachineBasicBlock::iterator &I) {
MachineInstr *MI = *I;
unsigned DestReg = getFPReg(MI->getOperand(0));
MI->RemoveOperand(0); // Remove the explicit ST(0) operand
// Result gets pushed on the stack...
pushReg(DestReg);
}
/// handleOneArgFP - fst ST(0), <mem>
//
void FPS::handleOneArgFP(MachineBasicBlock::iterator &I) {
MachineInstr *MI = *I;
assert(MI->getNumOperands() == 5 && "Can only handle fst* instructions!");
unsigned Reg = getFPReg(MI->getOperand(4));
bool KillsSrc = false;
for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
E = LV->killed_end(MI); KI != E; ++KI)
KillsSrc |= KI->second == X86::FP0+Reg;
// FSTPr80 and FISTPr64 are strange because there are no non-popping versions.
// If we have one _and_ we don't want to pop the operand, duplicate the value
// on the stack instead of moving it. This ensure that popping the value is
// always ok.
//
if ((MI->getOpcode() == X86::FSTPr80 ||
MI->getOpcode() == X86::FISTPr64) && !KillsSrc) {
duplicateToTop(Reg, 7 /*temp register*/, I);
} else {
moveToTop(Reg, I); // Move to the top of the stack...
}
MI->RemoveOperand(4); // Remove explicit ST(0) operand
if (MI->getOpcode() == X86::FSTPr80 || MI->getOpcode() == X86::FISTPr64) {
assert(StackTop > 0 && "Stack empty??");
--StackTop;
} else if (KillsSrc) { // Last use of operand?
popStackAfter(I);
}
}
//===----------------------------------------------------------------------===//
// Define tables of various ways to map pseudo instructions
//
// ForwardST0Table - Map: A = B op C into: ST(0) = ST(0) op ST(i)
static const TableEntry ForwardST0Table[] = {
{ X86::FpADD, X86::FADDST0r },
{ X86::FpDIV, X86::FDIVST0r },
{ X86::FpMUL, X86::FMULST0r },
{ X86::FpSUB, X86::FSUBST0r },
{ X86::FpUCOM, X86::FUCOMr },
};
// ReverseST0Table - Map: A = B op C into: ST(0) = ST(i) op ST(0)
static const TableEntry ReverseST0Table[] = {
{ X86::FpADD, X86::FADDST0r }, // commutative
{ X86::FpDIV, X86::FDIVRST0r },
{ X86::FpMUL, X86::FMULST0r }, // commutative
{ X86::FpSUB, X86::FSUBRST0r },
{ X86::FpUCOM, ~0 },
};
// ForwardSTiTable - Map: A = B op C into: ST(i) = ST(0) op ST(i)
static const TableEntry ForwardSTiTable[] = {
{ X86::FpADD, X86::FADDrST0 }, // commutative
{ X86::FpDIV, X86::FDIVRrST0 },
{ X86::FpMUL, X86::FMULrST0 }, // commutative
{ X86::FpSUB, X86::FSUBRrST0 },
{ X86::FpUCOM, X86::FUCOMr },
};
// ReverseSTiTable - Map: A = B op C into: ST(i) = ST(i) op ST(0)
static const TableEntry ReverseSTiTable[] = {
{ X86::FpADD, X86::FADDrST0 },
{ X86::FpDIV, X86::FDIVrST0 },
{ X86::FpMUL, X86::FMULrST0 },
{ X86::FpSUB, X86::FSUBrST0 },
{ X86::FpUCOM, ~0 },
};
/// handleTwoArgFP - Handle instructions like FADD and friends which are virtual
/// instructions which need to be simplified and possibly transformed.
///
/// Result: ST(0) = fsub ST(0), ST(i)
/// ST(i) = fsub ST(0), ST(i)
/// ST(0) = fsubr ST(0), ST(i)
/// ST(i) = fsubr ST(0), ST(i)
///
/// In addition to three address instructions, this also handles the FpUCOM
/// instruction which only has two operands, but no destination. This
/// instruction is also annoying because there is no "reverse" form of it
/// available.
///
void FPS::handleTwoArgFP(MachineBasicBlock::iterator &I) {
ASSERT_SORTED(ForwardST0Table); ASSERT_SORTED(ReverseST0Table);
ASSERT_SORTED(ForwardSTiTable); ASSERT_SORTED(ReverseSTiTable);
MachineInstr *MI = *I;
unsigned NumOperands = MI->getNumOperands();
assert(NumOperands == 3 ||
(NumOperands == 2 && MI->getOpcode() == X86::FpUCOM) &&
"Illegal TwoArgFP instruction!");
unsigned Dest = getFPReg(MI->getOperand(0));
unsigned Op0 = getFPReg(MI->getOperand(NumOperands-2));
unsigned Op1 = getFPReg(MI->getOperand(NumOperands-1));
bool KillsOp0 = false, KillsOp1 = false;
for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
E = LV->killed_end(MI); KI != E; ++KI) {
KillsOp0 |= (KI->second == X86::FP0+Op0);
KillsOp1 |= (KI->second == X86::FP0+Op1);
}
// If this is an FpUCOM instruction, we must make sure the first operand is on
// the top of stack, the other one can be anywhere...
if (MI->getOpcode() == X86::FpUCOM)
moveToTop(Op0, I);
unsigned TOS = getStackEntry(0);
// One of our operands must be on the top of the stack. If neither is yet, we
// need to move one.
if (Op0 != TOS && Op1 != TOS) { // No operand at TOS?
// We can choose to move either operand to the top of the stack. If one of
// the operands is killed by this instruction, we want that one so that we
// can update right on top of the old version.
if (KillsOp0) {
moveToTop(Op0, I); // Move dead operand to TOS.
TOS = Op0;
} else if (KillsOp1) {
moveToTop(Op1, I);
TOS = Op1;
} else {
// All of the operands are live after this instruction executes, so we
// cannot update on top of any operand. Because of this, we must
// duplicate one of the stack elements to the top. It doesn't matter
// which one we pick.
//
duplicateToTop(Op0, Dest, I);
Op0 = TOS = Dest;
KillsOp0 = true;
}
} else if (!KillsOp0 && !KillsOp1 && MI->getOpcode() != X86::FpUCOM) {
// If we DO have one of our operands at the top of the stack, but we don't
// have a dead operand, we must duplicate one of the operands to a new slot
// on the stack.
duplicateToTop(Op0, Dest, I);
Op0 = TOS = Dest;
KillsOp0 = true;
}
// Now we know that one of our operands is on the top of the stack, and at
// least one of our operands is killed by this instruction.
assert((TOS == Op0 || TOS == Op1) &&
(KillsOp0 || KillsOp1 || MI->getOpcode() == X86::FpUCOM) &&
"Stack conditions not set up right!");
// We decide which form to use based on what is on the top of the stack, and
// which operand is killed by this instruction.
const TableEntry *InstTable;
bool isForward = TOS == Op0;
bool updateST0 = (TOS == Op0 && !KillsOp1) || (TOS == Op1 && !KillsOp0);
if (updateST0) {
if (isForward)
InstTable = ForwardST0Table;
else
InstTable = ReverseST0Table;
} else {
if (isForward)
InstTable = ForwardSTiTable;
else
InstTable = ReverseSTiTable;
}
int Opcode = Lookup(InstTable, ARRAY_SIZE(ForwardST0Table), MI->getOpcode());
assert(Opcode != -1 && "Unknown TwoArgFP pseudo instruction!");
// NotTOS - The register which is not on the top of stack...
unsigned NotTOS = (TOS == Op0) ? Op1 : Op0;
// Replace the old instruction with a new instruction
*I = BuildMI(Opcode, 1).addReg(getSTReg(NotTOS));
// If both operands are killed, pop one off of the stack in addition to
// overwriting the other one.
if (KillsOp0 && KillsOp1 && Op0 != Op1) {
assert(!updateST0 && "Should have updated other operand!");
popStackAfter(I); // Pop the top of stack
}
// Insert an explicit pop of the "updated" operand for FUCOM
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+1, MI);
}
}
}
// Update stack information so that we know the destination register is now on
// the stack.
if (MI->getOpcode() != X86::FpUCOM) {
unsigned UpdatedSlot = getSlot(updateST0 ? TOS : NotTOS);
assert(UpdatedSlot < StackTop && Dest < 7);
Stack[UpdatedSlot] = Dest;
RegMap[Dest] = UpdatedSlot;
}
delete MI; // Remove the old instruction
}
/// handleSpecialFP - Handle special instructions which behave unlike other
/// floating point instructions. This is primarily inteaded for use by pseudo
/// instructions.
///
void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
MachineInstr *MI = *I;
switch (MI->getOpcode()) {
default: assert(0 && "Unknown SpecialFP instruction!");
case X86::FpGETRESULT: // Appears immediately after a call returning FP type!
assert(StackTop == 0 && "Stack should be empty after a call!");
pushReg(getFPReg(MI->getOperand(0)));
break;
case X86::FpSETRESULT:
assert(StackTop == 1 && "Stack should have one element on it to return!");
--StackTop; // "Forget" we have something on the top of stack!
break;
case X86::FpMOV: {
unsigned SrcReg = getFPReg(MI->getOperand(1));
unsigned DestReg = getFPReg(MI->getOperand(0));
bool KillsSrc = false;
for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
E = LV->killed_end(MI); KI != E; ++KI)
KillsSrc |= KI->second == X86::FP0+SrcReg;
if (KillsSrc) {
// If the input operand is killed, we can just change the owner of the
// incoming stack slot into the result.
unsigned Slot = getSlot(SrcReg);
assert(Slot < 7 && DestReg < 7 && "FpMOV operands invalid!");
Stack[Slot] = DestReg;
RegMap[DestReg] = Slot;
} else {
// For FMOV we just duplicate the specified value to a new stack slot.
// This could be made better, but would require substantial changes.
duplicateToTop(SrcReg, DestReg, I);
}
break;
}
}
I = MBB->erase(I)-1; // Remove the pseudo instruction
}
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