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[AArch64][PAC] Cleanup AArch64AsmPrinter::emitPtrauthDiscriminator (NFC) #160900

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[AArch64][PAC] Cleanup AArch64AsmPrinter::emitPtrauthDiscriminator (NFC) #160900

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46 changes: 25 additions & 21 deletions llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -155,6 +155,13 @@ class AArch64AsmPrinter : public AsmPrinter {

void emitSled(const MachineInstr &MI, SledKind Kind);

bool isPtrauthRegSafe(Register Reg) const {
if (STI->isX16X17Safer())
return Reg == AArch64::X16 || Reg == AArch64::X17;

return true;
}

// Emit the sequence for BRA/BLRA (authenticate + branch/call).
void emitPtrauthBranch(const MachineInstr *MI);

Expand All @@ -180,13 +187,15 @@ class AArch64AsmPrinter : public AsmPrinter {

// Emit the sequence to compute the discriminator.
//
// The returned register is either unmodified AddrDisc or ScratchReg.
// The Scratch register passed to this function must be safe, see
// isPtrauthRegSafe(Reg) function.
//
// The returned register is either ScratchReg or AddrDisc. Furthermore, it
// is safe, unless unsafe AddrDisc was passed-through unmodified.
//
// If the expanded pseudo is allowed to clobber AddrDisc register, setting
// MayUseAddrAsScratch may save one MOV instruction, provided the address
// is already in x16/x17 (i.e. return x16/x17 which is the *modified* AddrDisc
// register at the same time) or the OS doesn't make it safer to use x16/x17
// (see AArch64Subtarget::isX16X17Safer()):
// MayUseAddrAsScratch may save one MOV instruction, provided
// isPtrauthRegSafe(AddrDisc) is true:
//
// mov x17, x16
// movk x17, #1234, lsl #48
Expand All @@ -195,7 +204,7 @@ class AArch64AsmPrinter : public AsmPrinter {
// can be replaced by
//
// movk x16, #1234, lsl #48
Register emitPtrauthDiscriminator(uint16_t Disc, Register AddrDisc,
Register emitPtrauthDiscriminator(uint64_t Disc, Register AddrDisc,
Register ScratchReg,
bool MayUseAddrAsScratch = false);

Expand Down Expand Up @@ -1902,12 +1911,14 @@ void AArch64AsmPrinter::emitFMov0AsFMov(const MachineInstr &MI,
EmitToStreamer(*OutStreamer, FMov);
}

Register AArch64AsmPrinter::emitPtrauthDiscriminator(uint16_t Disc,
Register AArch64AsmPrinter::emitPtrauthDiscriminator(uint64_t Disc,
Register AddrDisc,
Register ScratchReg,
bool MayUseAddrAsScratch) {
assert(ScratchReg == AArch64::X16 || ScratchReg == AArch64::X17 ||
!STI->isX16X17Safer());
assert(isPtrauthRegSafe(ScratchReg) &&
"Safe scratch register must be provided by the caller");
assert(isUInt<16>(Disc) && "Constant discriminator is too wide");

// So far we've used NoRegister in pseudos. Now we need real encodings.
if (AddrDisc == AArch64::NoRegister)
AddrDisc = AArch64::XZR;
Expand All @@ -1926,13 +1937,13 @@ Register AArch64AsmPrinter::emitPtrauthDiscriminator(uint16_t Disc,
// If there are both, emit a blend into the scratch register.

// Check if we can save one MOV instruction.
assert(MayUseAddrAsScratch || ScratchReg != AddrDisc);
bool AddrDiscIsSafe = AddrDisc == AArch64::X16 || AddrDisc == AArch64::X17 ||
!STI->isX16X17Safer();
if (MayUseAddrAsScratch && AddrDiscIsSafe)
if (MayUseAddrAsScratch && isPtrauthRegSafe(AddrDisc)) {
ScratchReg = AddrDisc;
else
} else {
emitMovXReg(ScratchReg, AddrDisc);
assert(ScratchReg != AddrDisc &&
"Forbidden to clobber AddrDisc, but have to");
}

emitMOVK(ScratchReg, Disc, 48);
return ScratchReg;
Expand Down Expand Up @@ -2151,7 +2162,6 @@ void AArch64AsmPrinter::emitPtrauthAuthResign(
}

// Compute aut discriminator
assert(isUInt<16>(AUTDisc));
Register AUTDiscReg = emitPtrauthDiscriminator(
AUTDisc, AUTAddrDisc->getReg(), Scratch, AUTAddrDisc->isKill());
bool AUTZero = AUTDiscReg == AArch64::XZR;
Expand Down Expand Up @@ -2188,7 +2198,6 @@ void AArch64AsmPrinter::emitPtrauthAuthResign(
return;

// Compute pac discriminator
assert(isUInt<16>(PACDisc));
Register PACDiscReg =
emitPtrauthDiscriminator(PACDisc, PACAddrDisc, Scratch);
bool PACZero = PACDiscReg == AArch64::XZR;
Expand Down Expand Up @@ -2223,7 +2232,6 @@ void AArch64AsmPrinter::emitPtrauthSign(const MachineInstr *MI) {
"Neither X16 nor X17 is available as a scratch register");

// Compute pac discriminator
assert(isUInt<16>(Disc));
Register DiscReg = emitPtrauthDiscriminator(
Disc, AddrDisc, ScratchReg, /*MayUseAddrAsScratch=*/AddrDiscKilled);
bool IsZeroDisc = DiscReg == AArch64::XZR;
Expand All @@ -2249,7 +2257,6 @@ void AArch64AsmPrinter::emitPtrauthBranch(const MachineInstr *MI) {
"Invalid auth call key");

uint64_t Disc = MI->getOperand(2).getImm();
assert(isUInt<16>(Disc));

unsigned AddrDisc = MI->getOperand(3).getReg();

Expand Down Expand Up @@ -2422,8 +2429,6 @@ void AArch64AsmPrinter::LowerMOVaddrPAC(const MachineInstr &MI) {
const auto Key = (AArch64PACKey::ID)KeyC;
const unsigned AddrDisc = MI.getOperand(2).getReg();
const uint64_t Disc = MI.getOperand(3).getImm();
assert(isUInt<16>(Disc) &&
"constant discriminator is out of range [0, 0xffff]");

const int64_t Offset = GAOp.getOffset();
GAOp.setOffset(0);
Expand Down Expand Up @@ -2995,7 +3000,6 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
"Invalid auth key for tail-call return");

const uint64_t Disc = MI->getOperand(3).getImm();
assert(isUInt<16>(Disc) && "Integer discriminator is too wide");

Register AddrDisc = MI->getOperand(4).getReg();

Expand Down
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