[APFloat] Add support for f8E4M3 IEEE 754 type (#97179)

This PR adds `f8E4M3` type to APFloat.

`f8E4M3` type  follows IEEE 754 convention

```c
f8E4M3 (IEEE 754)
- Exponent bias: 7
- Maximum stored exponent value: 14 (binary 1110)
- Maximum unbiased exponent value: 14 - 7 = 7
- Minimum stored exponent value: 1 (binary 0001)
- Minimum unbiased exponent value: 1 − 7 = −6
- Precision specifies the total number of bits used for the significand (mantisa), 
    including implicit leading integer bit = 3 + 1 = 4
- Follows IEEE 754 conventions for representation of special values
- Has Positive and Negative zero
- Has Positive and Negative infinity
- Has NaNs

Additional details:
- Max exp (unbiased): 7
- Min exp (unbiased): -6
- Infinities (+/-): S.1111.000
- Zeros (+/-): S.0000.000
- NaNs: S.1111.{001, 010, 011, 100, 101, 110, 111}
- Max normal number: S.1110.111 = +/-2^(7) x (1 + 0.875) = +/-240
- Min normal number: S.0001.000 = +/-2^(-6)
- Max subnormal number: S.0000.111 = +/-2^(-6) x 0.875 = +/-2^(-9) x 7
- Min subnormal number: S.0000.001 = +/-2^(-6) x 0.125 = +/-2^(-9)
```

Related PRs:
- [PR-97118](#97118) Add f8E4M3
IEEE 754 type to mlir

clang/include/clang/AST/Stmt.h

@@ -460,10 +460,10 @@ class alignas(void *) Stmt {
     unsigned : NumExprBits;
 
     static_assert(
-        llvm::APFloat::S_MaxSemantics < 16,
-        "Too many Semantics enum values to fit in bitfield of size 4");
+        llvm::APFloat::S_MaxSemantics < 32,
+        "Too many Semantics enum values to fit in bitfield of size 5");
     LLVM_PREFERRED_TYPE(llvm::APFloat::Semantics)
-    unsigned Semantics : 4; // Provides semantics for APFloat construction
+    unsigned Semantics : 5; // Provides semantics for APFloat construction
     LLVM_PREFERRED_TYPE(bool)
     unsigned IsExact : 1;
   };

clang/lib/AST/MicrosoftMangle.cpp

@@ -981,6 +981,7 @@ void MicrosoftCXXNameMangler::mangleFloat(llvm::APFloat Number) {
   case APFloat::S_IEEEquad: Out << 'Y'; break;
   case APFloat::S_PPCDoubleDouble: Out << 'Z'; break;
   case APFloat::S_Float8E5M2:
+  case APFloat::S_Float8E4M3:
   case APFloat::S_Float8E4M3FN:
   case APFloat::S_Float8E5M2FNUZ:
   case APFloat::S_Float8E4M3FNUZ:

llvm/include/llvm/ADT/APFloat.h

@@ -166,6 +166,9 @@ struct APFloatBase {
     // This format's exponent bias is 16, instead of the 15 (2 ** (5 - 1) - 1)
     // that IEEE precedent would imply.
     S_Float8E5M2FNUZ,
+    // 8-bit floating point number following IEEE-754 conventions with bit
+    // layout S1E4M3.
+    S_Float8E4M3,
     // 8-bit floating point number mostly following IEEE-754 conventions with
     // bit layout S1E4M3 as described in https://arxiv.org/abs/2209.05433.
     // Unlike IEEE-754 types, there are no infinity values, and NaN is
@@ -217,6 +220,7 @@ struct APFloatBase {
   static const fltSemantics &PPCDoubleDouble() LLVM_READNONE;
   static const fltSemantics &Float8E5M2() LLVM_READNONE;
   static const fltSemantics &Float8E5M2FNUZ() LLVM_READNONE;
+  static const fltSemantics &Float8E4M3() LLVM_READNONE;
   static const fltSemantics &Float8E4M3FN() LLVM_READNONE;
   static const fltSemantics &Float8E4M3FNUZ() LLVM_READNONE;
   static const fltSemantics &Float8E4M3B11FNUZ() LLVM_READNONE;
@@ -638,6 +642,7 @@ class IEEEFloat final : public APFloatBase {
   APInt convertPPCDoubleDoubleAPFloatToAPInt() const;
   APInt convertFloat8E5M2APFloatToAPInt() const;
   APInt convertFloat8E5M2FNUZAPFloatToAPInt() const;
+  APInt convertFloat8E4M3APFloatToAPInt() const;
   APInt convertFloat8E4M3FNAPFloatToAPInt() const;
   APInt convertFloat8E4M3FNUZAPFloatToAPInt() const;
   APInt convertFloat8E4M3B11FNUZAPFloatToAPInt() const;
@@ -656,6 +661,7 @@ class IEEEFloat final : public APFloatBase {
   void initFromPPCDoubleDoubleAPInt(const APInt &api);
   void initFromFloat8E5M2APInt(const APInt &api);
   void initFromFloat8E5M2FNUZAPInt(const APInt &api);
+  void initFromFloat8E4M3APInt(const APInt &api);
   void initFromFloat8E4M3FNAPInt(const APInt &api);
   void initFromFloat8E4M3FNUZAPInt(const APInt &api);
   void initFromFloat8E4M3B11FNUZAPInt(const APInt &api);

llvm/lib/Support/APFloat.cpp

@@ -136,6 +136,7 @@ static constexpr fltSemantics semIEEEquad = {16383, -16382, 113, 128};
 static constexpr fltSemantics semFloat8E5M2 = {15, -14, 3, 8};
 static constexpr fltSemantics semFloat8E5M2FNUZ = {
     15, -15, 3, 8, fltNonfiniteBehavior::NanOnly, fltNanEncoding::NegativeZero};
+static constexpr fltSemantics semFloat8E4M3 = {7, -6, 4, 8};
 static constexpr fltSemantics semFloat8E4M3FN = {
     8, -6, 4, 8, fltNonfiniteBehavior::NanOnly, fltNanEncoding::AllOnes};
 static constexpr fltSemantics semFloat8E4M3FNUZ = {
@@ -208,6 +209,8 @@ const llvm::fltSemantics &APFloatBase::EnumToSemantics(Semantics S) {
     return Float8E5M2();
   case S_Float8E5M2FNUZ:
     return Float8E5M2FNUZ();
+  case S_Float8E4M3:
+    return Float8E4M3();
   case S_Float8E4M3FN:
     return Float8E4M3FN();
   case S_Float8E4M3FNUZ:
@@ -246,6 +249,8 @@ APFloatBase::SemanticsToEnum(const llvm::fltSemantics &Sem) {
     return S_Float8E5M2;
   else if (&Sem == &llvm::APFloat::Float8E5M2FNUZ())
     return S_Float8E5M2FNUZ;
+  else if (&Sem == &llvm::APFloat::Float8E4M3())
+    return S_Float8E4M3;
   else if (&Sem == &llvm::APFloat::Float8E4M3FN())
     return S_Float8E4M3FN;
   else if (&Sem == &llvm::APFloat::Float8E4M3FNUZ())
@@ -276,6 +281,7 @@ const fltSemantics &APFloatBase::PPCDoubleDouble() {
 }
 const fltSemantics &APFloatBase::Float8E5M2() { return semFloat8E5M2; }
 const fltSemantics &APFloatBase::Float8E5M2FNUZ() { return semFloat8E5M2FNUZ; }
+const fltSemantics &APFloatBase::Float8E4M3() { return semFloat8E4M3; }
 const fltSemantics &APFloatBase::Float8E4M3FN() { return semFloat8E4M3FN; }
 const fltSemantics &APFloatBase::Float8E4M3FNUZ() { return semFloat8E4M3FNUZ; }
 const fltSemantics &APFloatBase::Float8E4M3B11FNUZ() {
@@ -3617,6 +3623,11 @@ APInt IEEEFloat::convertFloat8E5M2FNUZAPFloatToAPInt() const {
   return convertIEEEFloatToAPInt<semFloat8E5M2FNUZ>();
 }
 
+APInt IEEEFloat::convertFloat8E4M3APFloatToAPInt() const {
+  assert(partCount() == 1);
+  return convertIEEEFloatToAPInt<semFloat8E4M3>();
+}
+
 APInt IEEEFloat::convertFloat8E4M3FNAPFloatToAPInt() const {
   assert(partCount() == 1);
   return convertIEEEFloatToAPInt<semFloat8E4M3FN>();
@@ -3681,6 +3692,9 @@ APInt IEEEFloat::bitcastToAPInt() const {
   if (semantics == (const llvm::fltSemantics *)&semFloat8E5M2FNUZ)
     return convertFloat8E5M2FNUZAPFloatToAPInt();
 
+  if (semantics == (const llvm::fltSemantics *)&semFloat8E4M3)
+    return convertFloat8E4M3APFloatToAPInt();
+
   if (semantics == (const llvm::fltSemantics *)&semFloat8E4M3FN)
     return convertFloat8E4M3FNAPFloatToAPInt();
 
@@ -3902,6 +3916,10 @@ void IEEEFloat::initFromFloat8E5M2FNUZAPInt(const APInt &api) {
   initFromIEEEAPInt<semFloat8E5M2FNUZ>(api);
 }
 
+void IEEEFloat::initFromFloat8E4M3APInt(const APInt &api) {
+  initFromIEEEAPInt<semFloat8E4M3>(api);
+}
+
 void IEEEFloat::initFromFloat8E4M3FNAPInt(const APInt &api) {
   initFromIEEEAPInt<semFloat8E4M3FN>(api);
 }
@@ -3951,6 +3969,8 @@ void IEEEFloat::initFromAPInt(const fltSemantics *Sem, const APInt &api) {
     return initFromFloat8E5M2APInt(api);
   if (Sem == &semFloat8E5M2FNUZ)
     return initFromFloat8E5M2FNUZAPInt(api);
+  if (Sem == &semFloat8E4M3)
+    return initFromFloat8E4M3APInt(api);
   if (Sem == &semFloat8E4M3FN)
     return initFromFloat8E4M3FNAPInt(api);
   if (Sem == &semFloat8E4M3FNUZ)

llvm/unittests/ADT/APFloatTest.cpp

@@ -2133,6 +2133,8 @@ TEST(APFloatTest, getZero) {
       {&APFloat::Float8E5M2(), true, true, {0x80ULL, 0}, 1},
       {&APFloat::Float8E5M2FNUZ(), false, false, {0, 0}, 1},
       {&APFloat::Float8E5M2FNUZ(), true, false, {0, 0}, 1},
+      {&APFloat::Float8E4M3(), false, true, {0, 0}, 1},
+      {&APFloat::Float8E4M3(), true, true, {0x80ULL, 0}, 1},
       {&APFloat::Float8E4M3FN(), false, true, {0, 0}, 1},
       {&APFloat::Float8E4M3FN(), true, true, {0x80ULL, 0}, 1},
       {&APFloat::Float8E4M3FNUZ(), false, false, {0, 0}, 1},
@@ -6532,6 +6534,34 @@ TEST(APFloatTest, Float8E5M2ToDouble) {
   EXPECT_TRUE(std::isnan(QNaN.convertToDouble()));
 }
 
+TEST(APFloatTest, Float8E4M3ToDouble) {
+  APFloat One(APFloat::Float8E4M3(), "1.0");
+  EXPECT_EQ(1.0, One.convertToDouble());
+  APFloat Two(APFloat::Float8E4M3(), "2.0");
+  EXPECT_EQ(2.0, Two.convertToDouble());
+  APFloat PosLargest = APFloat::getLargest(APFloat::Float8E4M3(), false);
+  EXPECT_EQ(240.0F, PosLargest.convertToDouble());
+  APFloat NegLargest = APFloat::getLargest(APFloat::Float8E4M3(), true);
+  EXPECT_EQ(-240.0F, NegLargest.convertToDouble());
+  APFloat PosSmallest =
+      APFloat::getSmallestNormalized(APFloat::Float8E4M3(), false);
+  EXPECT_EQ(0x1.p-6, PosSmallest.convertToDouble());
+  APFloat NegSmallest =
+      APFloat::getSmallestNormalized(APFloat::Float8E4M3(), true);
+  EXPECT_EQ(-0x1.p-6, NegSmallest.convertToDouble());
+
+  APFloat SmallestDenorm = APFloat::getSmallest(APFloat::Float8E4M3(), false);
+  EXPECT_TRUE(SmallestDenorm.isDenormal());
+  EXPECT_EQ(0x1.p-9, SmallestDenorm.convertToDouble());
+
+  APFloat PosInf = APFloat::getInf(APFloat::Float8E4M3());
+  EXPECT_EQ(std::numeric_limits<double>::infinity(), PosInf.convertToDouble());
+  APFloat NegInf = APFloat::getInf(APFloat::Float8E4M3(), true);
+  EXPECT_EQ(-std::numeric_limits<double>::infinity(), NegInf.convertToDouble());
+  APFloat QNaN = APFloat::getQNaN(APFloat::Float8E4M3());
+  EXPECT_TRUE(std::isnan(QNaN.convertToDouble()));
+}
+
 TEST(APFloatTest, Float8E4M3FNToDouble) {
   APFloat One(APFloat::Float8E4M3FN(), "1.0");
   EXPECT_EQ(1.0, One.convertToDouble());
@@ -6846,6 +6876,42 @@ TEST(APFloatTest, Float8E5M2ToFloat) {
   EXPECT_TRUE(std::isnan(QNaN.convertToFloat()));
 }
 
+TEST(APFloatTest, Float8E4M3ToFloat) {
+  APFloat PosZero = APFloat::getZero(APFloat::Float8E4M3());
+  APFloat PosZeroToFloat(PosZero.convertToFloat());
+  EXPECT_TRUE(PosZeroToFloat.isPosZero());
+  APFloat NegZero = APFloat::getZero(APFloat::Float8E4M3(), true);
+  APFloat NegZeroToFloat(NegZero.convertToFloat());
+  EXPECT_TRUE(NegZeroToFloat.isNegZero());
+
+  APFloat One(APFloat::Float8E4M3(), "1.0");
+  EXPECT_EQ(1.0F, One.convertToFloat());
+  APFloat Two(APFloat::Float8E4M3(), "2.0");
+  EXPECT_EQ(2.0F, Two.convertToFloat());
+
+  APFloat PosLargest = APFloat::getLargest(APFloat::Float8E4M3(), false);
+  EXPECT_EQ(240.0F, PosLargest.convertToFloat());
+  APFloat NegLargest = APFloat::getLargest(APFloat::Float8E4M3(), true);
+  EXPECT_EQ(-240.0F, NegLargest.convertToFloat());
+  APFloat PosSmallest =
+      APFloat::getSmallestNormalized(APFloat::Float8E4M3(), false);
+  EXPECT_EQ(0x1.p-6, PosSmallest.convertToFloat());
+  APFloat NegSmallest =
+      APFloat::getSmallestNormalized(APFloat::Float8E4M3(), true);
+  EXPECT_EQ(-0x1.p-6, NegSmallest.convertToFloat());
+
+  APFloat SmallestDenorm = APFloat::getSmallest(APFloat::Float8E4M3(), false);
+  EXPECT_TRUE(SmallestDenorm.isDenormal());
+  EXPECT_EQ(0x1.p-9, SmallestDenorm.convertToFloat());
+
+  APFloat PosInf = APFloat::getInf(APFloat::Float8E4M3());
+  EXPECT_EQ(std::numeric_limits<float>::infinity(), PosInf.convertToFloat());
+  APFloat NegInf = APFloat::getInf(APFloat::Float8E4M3(), true);
+  EXPECT_EQ(-std::numeric_limits<float>::infinity(), NegInf.convertToFloat());
+  APFloat QNaN = APFloat::getQNaN(APFloat::Float8E4M3());
+  EXPECT_TRUE(std::isnan(QNaN.convertToFloat()));
+}
+
 TEST(APFloatTest, Float8E4M3FNToFloat) {
   APFloat PosZero = APFloat::getZero(APFloat::Float8E4M3FN());
   APFloat PosZeroToFloat(PosZero.convertToFloat());