[WIP][CLANG][AArch64] Add the modal 8 bit floating-point scalar type

ARM ACLE PR#323[1] adds new modal types for 8-bit floating point intrinsic.

From the PR#323:
```
ACLE defines the `__fpm8` type, which can be used for the E5M2 and E4M3
8-bit floating-point formats. It is a storage and interchange only type
with no arithmetic operations other than intrinsic calls.
````

The type should be an opaque type and its format in undefined in Clang.
Only defined in the backend by a status/format register, for AArch64 the FPMR.

This patch is an attempt to the add the fpm8_t scalar type.
It has a parser and codegen for the new scalar type.

The patch it is lowering to and 8bit unsigned as it has no format.
But maybe we should add another opaque type.

[1]  ARM-software/acle#323

Author: CarolineConcatto

clang/include/clang/AST/ASTContext.h

@@ -1115,6 +1115,7 @@ class ASTContext : public RefCountedBase<ASTContext> {
   CanQualType SatShortFractTy, SatFractTy, SatLongFractTy;
   CanQualType SatUnsignedShortFractTy, SatUnsignedFractTy,
       SatUnsignedLongFractTy;
+  CanQualType Fpm8Ty;
   CanQualType HalfTy; // [OpenCL 6.1.1.1], ARM NEON
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3

clang/include/clang/AST/BuiltinTypes.def

@@ -221,6 +221,10 @@ FLOATING_TYPE(Float128, Float128Ty)
 // '__ibm128'
 FLOATING_TYPE(Ibm128, Ibm128Ty)
 
+
+// '__fpm8'
+UNSIGNED_TYPE(Fpm8, Fpm8Ty)
+
 //===- Language-specific types --------------------------------------------===//
 
 // This is the type of C++0x 'nullptr'.

clang/include/clang/AST/Type.h

@@ -2492,6 +2492,7 @@ class alignas(TypeAlignment) Type : public ExtQualsTypeCommonBase {
   bool isDoubleType() const;
   bool isBFloat16Type() const;
   bool isFloat128Type() const;
+  bool isFpm8Type() const;
   bool isIbm128Type() const;
   bool isRealType() const;         // C99 6.2.5p17 (real floating + integer)
   bool isArithmeticType() const;   // C99 6.2.5p18 (integer + floating)
@@ -7944,6 +7945,10 @@ inline bool Type::isBFloat16Type() const {
   return isSpecificBuiltinType(BuiltinType::BFloat16);
 }
 
+inline bool Type::isFpm8Type() const {
+  return isSpecificBuiltinType(BuiltinType::Fpm8);
+}
+
 inline bool Type::isFloat128Type() const {
   return isSpecificBuiltinType(BuiltinType::Float128);
 }

clang/include/clang/Basic/Specifiers.h

@@ -68,6 +68,7 @@ namespace clang {
     TST_Accum,   // ISO/IEC JTC1 SC22 WG14 N1169 Extension
     TST_Fract,
     TST_BFloat16,
+    TST_Fpm8,
     TST_float,
     TST_double,
     TST_float128,

clang/include/clang/Basic/TokenKinds.def

@@ -655,6 +655,7 @@ KEYWORD(__bool                      , KEYALTIVEC|KEYZVECTOR)
 // ARM NEON extensions.
 ALIAS("__fp16", half                , KEYALL)
 KEYWORD(__bf16                      , KEYALL)
+KEYWORD(__fpm8                      , KEYALL)
 
 // OpenCL Extension.
 KEYWORD(half                        , HALFSUPPORT)

clang/include/clang/Sema/DeclSpec.h

@@ -287,6 +287,7 @@ class DeclSpec {
   static const TST TST_bitint = clang::TST_bitint;
   static const TST TST_half = clang::TST_half;
   static const TST TST_BFloat16 = clang::TST_BFloat16;
+  static const TST TST_Fpm8 = clang::TST_Fpm8;
   static const TST TST_float = clang::TST_float;
   static const TST TST_double = clang::TST_double;
   static const TST TST_float16 = clang::TST_Float16;

clang/include/clang/Serialization/ASTBitCodes.h

@@ -1078,6 +1078,8 @@ enum PredefinedTypeIDs {
   /// \brief The '__ibm128' type
   PREDEF_TYPE_IBM128_ID = 74,
 
+  PREDEF_TYPE_FPM8_ID = 75,
+
 /// OpenCL image types with auto numeration
 #define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix)                   \
   PREDEF_TYPE_##Id##_ID,
@@ -1109,7 +1111,7 @@ enum PredefinedTypeIDs {
 ///
 /// Type IDs for non-predefined types will start at
 /// NUM_PREDEF_TYPE_IDs.
-const unsigned NUM_PREDEF_TYPE_IDS = 503;
+const unsigned NUM_PREDEF_TYPE_IDS = 504;
 
 // Ensure we do not overrun the predefined types we reserved
 // in the enum PredefinedTypeIDs above.

clang/lib/AST/ASTContext.cpp

@@ -1408,6 +1408,8 @@ void ASTContext::InitBuiltinTypes(const TargetInfo &Target,
   // half type (OpenCL 6.1.1.1) / ARM NEON __fp16
   InitBuiltinType(HalfTy, BuiltinType::Half);
 
+  InitBuiltinType(Fpm8Ty, BuiltinType::Fpm8);
+
   InitBuiltinType(BFloat16Ty, BuiltinType::BFloat16);
 
   // Builtin type used to help define __builtin_va_list.
@@ -1977,6 +1979,7 @@ TypeInfo ASTContext::getTypeInfoImpl(const Type *T) const {
       Width = Target->getBoolWidth();
       Align = Target->getBoolAlign();
       break;
+    case BuiltinType::Fpm8:
     case BuiltinType::Char_S:
     case BuiltinType::Char_U:
     case BuiltinType::UChar:
@@ -8129,6 +8132,7 @@ static char getObjCEncodingForPrimitiveType(const ASTContext *C,
     case BuiltinType::LongDouble: return 'D';
     case BuiltinType::NullPtr:    return '*'; // like char*
 
+    case BuiltinType::Fpm8:
     case BuiltinType::BFloat16:
     case BuiltinType::Float16:
     case BuiltinType::Float128:
@@ -11466,6 +11470,9 @@ static QualType DecodeTypeFromStr(const char *&Str, const ASTContext &Context,
     else
       Type = Context.CharTy;
     break;
+  case '£':
+    Type = Context.Fpm8Ty;
+    break;
   case 'b': // boolean
     assert(HowLong == 0 && !Signed && !Unsigned && "Bad modifiers for 'b'!");
     Type = Context.BoolTy;

clang/lib/AST/ItaniumMangle.cpp

@@ -3181,6 +3181,7 @@ void CXXNameMangler::mangleType(const BuiltinType *T) {
   case BuiltinType::SChar:
     Out << 'a';
     break;
+  case BuiltinType::Fpm8:
   case BuiltinType::WChar_S:
   case BuiltinType::WChar_U:
     Out << 'w';

clang/lib/AST/Type.cpp

@@ -3372,6 +3372,8 @@ StringRef BuiltinType::getName(const PrintingPolicy &Policy) const {
     return "unsigned __int128";
   case Half:
     return Policy.Half ? "half" : "__fp16";
+  case Fpm8:
+    return "__fpm8";
   case BFloat16:
     return "__bf16";
   case Float: