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[APFloat] Add APFloat support for FP6 data types #94735

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Jun 11, 2024
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[APFloat] Add APFloat support for FP6 data types #94735

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2 changes: 2 additions & 0 deletions clang/lib/AST/MicrosoftMangle.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -899,6 +899,8 @@ void MicrosoftCXXNameMangler::mangleFloat(llvm::APFloat Number) {
case APFloat::S_Float8E4M3FNUZ:
case APFloat::S_Float8E4M3B11FNUZ:
case APFloat::S_FloatTF32:
case APFloat::S_Float6E3M2FN:
case APFloat::S_Float6E2M3FN:
llvm_unreachable("Tried to mangle unexpected APFloat semantics");
}

Expand Down
25 changes: 25 additions & 0 deletions llvm/include/llvm/ADT/APFloat.h
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Expand Up @@ -189,6 +189,14 @@ struct APFloatBase {
// improved range compared to half (16-bit) formats, at (potentially)
// greater throughput than single precision (32-bit) formats.
S_FloatTF32,
// 6-bit floating point number with bit layout S1E3M2. Unlike IEEE-754
// types, there are no infinity or NaN values. The format is detailed in
// https://www.opencompute.org/documents/ocp-microscaling-formats-mx-v1-0-spec-final-pdf
S_Float6E3M2FN,
// 6-bit floating point number with bit layout S1E2M3. Unlike IEEE-754
// types, there are no infinity or NaN values. The format is detailed in
// https://www.opencompute.org/documents/ocp-microscaling-formats-mx-v1-0-spec-final-pdf
S_Float6E2M3FN,

S_x87DoubleExtended,
S_MaxSemantics = S_x87DoubleExtended,
Expand All @@ -209,6 +217,8 @@ struct APFloatBase {
static const fltSemantics &Float8E4M3FNUZ() LLVM_READNONE;
static const fltSemantics &Float8E4M3B11FNUZ() LLVM_READNONE;
static const fltSemantics &FloatTF32() LLVM_READNONE;
static const fltSemantics &Float6E3M2FN() LLVM_READNONE;
static const fltSemantics &Float6E2M3FN() LLVM_READNONE;
static const fltSemantics &x87DoubleExtended() LLVM_READNONE;

/// A Pseudo fltsemantic used to construct APFloats that cannot conflict with
Expand Down Expand Up @@ -627,6 +637,8 @@ class IEEEFloat final : public APFloatBase {
APInt convertFloat8E4M3FNUZAPFloatToAPInt() const;
APInt convertFloat8E4M3B11FNUZAPFloatToAPInt() const;
APInt convertFloatTF32APFloatToAPInt() const;
APInt convertFloat6E3M2FNAPFloatToAPInt() const;
APInt convertFloat6E2M3FNAPFloatToAPInt() const;
void initFromAPInt(const fltSemantics *Sem, const APInt &api);
template <const fltSemantics &S> void initFromIEEEAPInt(const APInt &api);
void initFromHalfAPInt(const APInt &api);
Expand All @@ -642,6 +654,8 @@ class IEEEFloat final : public APFloatBase {
void initFromFloat8E4M3FNUZAPInt(const APInt &api);
void initFromFloat8E4M3B11FNUZAPInt(const APInt &api);
void initFromFloatTF32APInt(const APInt &api);
void initFromFloat6E3M2FNAPInt(const APInt &api);
void initFromFloat6E2M3FNAPInt(const APInt &api);

void assign(const IEEEFloat &);
void copySignificand(const IEEEFloat &);
Expand Down Expand Up @@ -1039,6 +1053,17 @@ class APFloat : public APFloatBase {
/// \param Semantics - type float semantics
static APFloat getAllOnesValue(const fltSemantics &Semantics);

static bool hasNanOrInf(const fltSemantics &Sem) {
switch (SemanticsToEnum(Sem)) {
default:
return true;
// Below Semantics do not support {NaN or Inf}
case APFloat::S_Float6E3M2FN:
case APFloat::S_Float6E2M3FN:
return false;
}
}

/// Used to insert APFloat objects, or objects that contain APFloat objects,
/// into FoldingSets.
void Profile(FoldingSetNodeID &NID) const;
Expand Down
87 changes: 74 additions & 13 deletions llvm/lib/Support/APFloat.cpp
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Expand Up @@ -68,6 +68,10 @@ enum class fltNonfiniteBehavior {
// `fltNanEncoding` enum. We treat all NaNs as quiet, as the available
// encodings do not distinguish between signalling and quiet NaN.
NanOnly,

// This behavior is present in Float6E3M2FN and Float6E2M3FN types,
// which do not support Inf or NaN values.
FiniteOnly,
};

// How NaN values are represented. This is curently only used in combination
Expand Down Expand Up @@ -139,6 +143,10 @@ static constexpr fltSemantics semFloat8E4M3FNUZ = {
static constexpr fltSemantics semFloat8E4M3B11FNUZ = {
4, -10, 4, 8, fltNonfiniteBehavior::NanOnly, fltNanEncoding::NegativeZero};
static constexpr fltSemantics semFloatTF32 = {127, -126, 11, 19};
static constexpr fltSemantics semFloat6E3M2FN = {
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4, -2, 3, 6, fltNonfiniteBehavior::FiniteOnly};
static constexpr fltSemantics semFloat6E2M3FN = {
2, 0, 4, 6, fltNonfiniteBehavior::FiniteOnly};
static constexpr fltSemantics semX87DoubleExtended = {16383, -16382, 64, 80};
static constexpr fltSemantics semBogus = {0, 0, 0, 0};

Expand Down Expand Up @@ -206,6 +214,10 @@ const llvm::fltSemantics &APFloatBase::EnumToSemantics(Semantics S) {
return Float8E4M3B11FNUZ();
case S_FloatTF32:
return FloatTF32();
case S_Float6E3M2FN:
return Float6E3M2FN();
case S_Float6E2M3FN:
return Float6E2M3FN();
case S_x87DoubleExtended:
return x87DoubleExtended();
}
Expand Down Expand Up @@ -238,6 +250,10 @@ APFloatBase::SemanticsToEnum(const llvm::fltSemantics &Sem) {
return S_Float8E4M3B11FNUZ;
else if (&Sem == &llvm::APFloat::FloatTF32())
return S_FloatTF32;
else if (&Sem == &llvm::APFloat::Float6E3M2FN())
return S_Float6E3M2FN;
else if (&Sem == &llvm::APFloat::Float6E2M3FN())
return S_Float6E2M3FN;
else if (&Sem == &llvm::APFloat::x87DoubleExtended())
return S_x87DoubleExtended;
else
Expand All @@ -260,6 +276,8 @@ const fltSemantics &APFloatBase::Float8E4M3B11FNUZ() {
return semFloat8E4M3B11FNUZ;
}
const fltSemantics &APFloatBase::FloatTF32() { return semFloatTF32; }
const fltSemantics &APFloatBase::Float6E3M2FN() { return semFloat6E3M2FN; }
const fltSemantics &APFloatBase::Float6E2M3FN() { return semFloat6E2M3FN; }
const fltSemantics &APFloatBase::x87DoubleExtended() {
return semX87DoubleExtended;
}
Expand Down Expand Up @@ -878,6 +896,9 @@ void IEEEFloat::copySignificand(const IEEEFloat &rhs) {
for the significand. If double or longer, this is a signalling NaN,
which may not be ideal. If float, this is QNaN(0). */
void IEEEFloat::makeNaN(bool SNaN, bool Negative, const APInt *fill) {
if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::FiniteOnly)
llvm_unreachable("This floating point format does not support NaN");

category = fcNaN;
sign = Negative;
exponent = exponentNaN();
Expand Down Expand Up @@ -1499,16 +1520,18 @@ static void tcSetLeastSignificantBits(APInt::WordType *dst, unsigned parts,
/* Handle overflow. Sign is preserved. We either become infinity or
the largest finite number. */
IEEEFloat::opStatus IEEEFloat::handleOverflow(roundingMode rounding_mode) {
/* Infinity? */
if (rounding_mode == rmNearestTiesToEven ||
rounding_mode == rmNearestTiesToAway ||
(rounding_mode == rmTowardPositive && !sign) ||
(rounding_mode == rmTowardNegative && sign)) {
if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::NanOnly)
makeNaN(false, sign);
else
category = fcInfinity;
return (opStatus) (opOverflow | opInexact);
if (semantics->nonFiniteBehavior != fltNonfiniteBehavior::FiniteOnly) {
/* Infinity? */
if (rounding_mode == rmNearestTiesToEven ||
rounding_mode == rmNearestTiesToAway ||
(rounding_mode == rmTowardPositive && !sign) ||
(rounding_mode == rmTowardNegative && sign)) {
if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::NanOnly)
makeNaN(false, sign);
else
category = fcInfinity;
return static_cast<opStatus>(opOverflow | opInexact);
}
}

/* Otherwise we become the largest finite number. */
Expand Down Expand Up @@ -3518,13 +3541,15 @@ APInt IEEEFloat::convertIEEEFloatToAPInt() const {
myexponent = ::exponentZero(S) + bias;
mysignificand.fill(0);
} else if (category == fcInfinity) {
if (S.nonFiniteBehavior == fltNonfiniteBehavior::NanOnly) {
if (S.nonFiniteBehavior == fltNonfiniteBehavior::NanOnly ||
S.nonFiniteBehavior == fltNonfiniteBehavior::FiniteOnly)
llvm_unreachable("semantics don't support inf!");
}
myexponent = ::exponentInf(S) + bias;
mysignificand.fill(0);
} else {
assert(category == fcNaN && "Unknown category!");
if (S.nonFiniteBehavior == fltNonfiniteBehavior::FiniteOnly)
llvm_unreachable("semantics don't support NaN!");
myexponent = ::exponentNaN(S) + bias;
std::copy_n(significandParts(), mysignificand.size(),
mysignificand.begin());
Expand Down Expand Up @@ -3605,6 +3630,16 @@ APInt IEEEFloat::convertFloatTF32APFloatToAPInt() const {
return convertIEEEFloatToAPInt<semFloatTF32>();
}

APInt IEEEFloat::convertFloat6E3M2FNAPFloatToAPInt() const {
assert(partCount() == 1);
return convertIEEEFloatToAPInt<semFloat6E3M2FN>();
}

APInt IEEEFloat::convertFloat6E2M3FNAPFloatToAPInt() const {
assert(partCount() == 1);
return convertIEEEFloatToAPInt<semFloat6E2M3FN>();
}

// This function creates an APInt that is just a bit map of the floating
// point constant as it would appear in memory. It is not a conversion,
// and treating the result as a normal integer is unlikely to be useful.
Expand Down Expand Up @@ -3646,6 +3681,12 @@ APInt IEEEFloat::bitcastToAPInt() const {
if (semantics == (const llvm::fltSemantics *)&semFloatTF32)
return convertFloatTF32APFloatToAPInt();

if (semantics == (const llvm::fltSemantics *)&semFloat6E3M2FN)
return convertFloat6E3M2FNAPFloatToAPInt();

if (semantics == (const llvm::fltSemantics *)&semFloat6E2M3FN)
return convertFloat6E2M3FNAPFloatToAPInt();

assert(semantics == (const llvm::fltSemantics*)&semX87DoubleExtended &&
"unknown format!");
return convertF80LongDoubleAPFloatToAPInt();
Expand Down Expand Up @@ -3862,6 +3903,14 @@ void IEEEFloat::initFromFloatTF32APInt(const APInt &api) {
initFromIEEEAPInt<semFloatTF32>(api);
}

void IEEEFloat::initFromFloat6E3M2FNAPInt(const APInt &api) {
initFromIEEEAPInt<semFloat6E3M2FN>(api);
}

void IEEEFloat::initFromFloat6E2M3FNAPInt(const APInt &api) {
initFromIEEEAPInt<semFloat6E2M3FN>(api);
}

/// Treat api as containing the bits of a floating point number.
void IEEEFloat::initFromAPInt(const fltSemantics *Sem, const APInt &api) {
assert(api.getBitWidth() == Sem->sizeInBits);
Expand Down Expand Up @@ -3891,6 +3940,10 @@ void IEEEFloat::initFromAPInt(const fltSemantics *Sem, const APInt &api) {
return initFromFloat8E4M3B11FNUZAPInt(api);
if (Sem == &semFloatTF32)
return initFromFloatTF32APInt(api);
if (Sem == &semFloat6E3M2FN)
return initFromFloat6E3M2FNAPInt(api);
if (Sem == &semFloat6E2M3FN)
return initFromFloat6E2M3FNAPInt(api);

llvm_unreachable(nullptr);
}
Expand Down Expand Up @@ -4328,7 +4381,8 @@ int IEEEFloat::getExactLog2Abs() const {
bool IEEEFloat::isSignaling() const {
if (!isNaN())
return false;
if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::NanOnly)
if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::NanOnly ||
semantics->nonFiniteBehavior == fltNonfiniteBehavior::FiniteOnly)
return false;

// IEEE-754R 2008 6.2.1: A signaling NaN bit string should be encoded with the
Expand Down Expand Up @@ -4387,6 +4441,10 @@ IEEEFloat::opStatus IEEEFloat::next(bool nextDown) {
// nextUp(getLargest()) == NAN
makeNaN();
break;
} else if (semantics->nonFiniteBehavior ==
fltNonfiniteBehavior::FiniteOnly) {
// nextUp(getLargest()) == getLargest()
break;
} else {
// nextUp(getLargest()) == INFINITY
APInt::tcSet(significandParts(), 0, partCount());
Expand Down Expand Up @@ -4477,6 +4535,9 @@ APFloatBase::ExponentType IEEEFloat::exponentZero() const {
}

void IEEEFloat::makeInf(bool Negative) {
if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::FiniteOnly)
llvm_unreachable("This floating point format does not support Inf");

if (semantics->nonFiniteBehavior == fltNonfiniteBehavior::NanOnly) {
// There is no Inf, so make NaN instead.
makeNaN(false, Negative);
Expand Down
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