[clang][AVR] Redefine [u]int16_t to be compatible with avr-gcc

[efriedma]

LGTM, thanks.

clang/include/clang/Basic/TargetInfo.h

struct TransferrableTargetInfo {
   enum RealType {
     NoFloat = 255,
     Float = 0,
     Double,
     LongDouble,
     Float128
   };
 protected:
   IntType SizeType, IntMaxType, PtrDiffType, IntPtrType, WCharType,
-          WIntType, Char16Type, Char32Type, Int64Type, SigAtomicType,
+          WIntType, Char16Type, Char32Type, Int64Type, Int16Type, SigAtomicType,
           ProcessIDType;
 
   /// Whether Objective-C's built-in boolean type should be signed char.
   ///
   /// Otherwise, when this flag is not set, the normal built-in boolean type is
   /// used.
   unsigned UseSignedCharForObjCBool : 1;
 
public:
   IntType getWCharType() const { return WCharType; }
   IntType getWIntType() const { return WIntType; }
   IntType getChar16Type() const { return Char16Type; }
   IntType getChar32Type() const { return Char32Type; }
   IntType getInt64Type() const { return Int64Type; }
   IntType getUInt64Type() const {
     return getCorrespondingUnsignedType(Int64Type);
   }
+  IntType getInt16Type() const { return Int16Type; }
+  IntType getUInt16Type() const {
+    return getCorrespondingUnsignedType(Int16Type);
+  }
   IntType getSigAtomicType() const { return SigAtomicType; }
   IntType getProcessIDType() const { return ProcessIDType; }
 
   static IntType getCorrespondingUnsignedType(IntType T) {
     switch (T) {
     case SignedChar:
       return UnsignedChar;
     case SignedShort:

clang/lib/Basic/TargetInfo.cpp

TargetInfo::TargetInfo(const llvm::Triple &T) : TargetOpts(), Triple(T) {
   PtrDiffType = SignedLong;
   IntMaxType = SignedLongLong;
   IntPtrType = SignedLong;
   WCharType = SignedInt;
   WIntType = SignedInt;
   Char16Type = UnsignedShort;
   Char32Type = UnsignedInt;
   Int64Type = SignedLongLong;
+  Int16Type = SignedShort;
   SigAtomicType = SignedInt;
   ProcessIDType = SignedInt;
   UseSignedCharForObjCBool = true;
   UseBitFieldTypeAlignment = true;
   UseZeroLengthBitfieldAlignment = false;
   UseLeadingZeroLengthBitfield = true;
   UseExplicitBitFieldAlignment = true;
   ZeroLengthBitfieldBoundary = 0;

clang/lib/Basic/Targets/AVR.h

AVRTargetInfo(const llvm::Triple &Triple, const TargetOptions &)
     LongDoubleWidth = 32;
     LongDoubleAlign = 8;
     LongDoubleFormat = &llvm::APFloat::IEEEsingle();
     SizeType = UnsignedInt;
     PtrDiffType = SignedInt;
     IntPtrType = SignedInt;
     Char16Type = UnsignedInt;
     WIntType = SignedInt;
+    Int16Type = SignedInt;
     Char32Type = UnsignedLong;
     SigAtomicType = SignedChar;
     resetDataLayout("e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8");
   }
 
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override;
 

clang/lib/Basic/Targets/AVR.cpp

 
 void AVRTargetInfo::getTargetDefines(const LangOptions &Opts,
                                      MacroBuilder &Builder) const {
   Builder.defineMacro("AVR");
   Builder.defineMacro("__AVR");
   Builder.defineMacro("__AVR__");
   Builder.defineMacro("__ELF__");
   Builder.defineMacro("__flash", "__attribute__((address_space(1)))");
-  Builder.defineMacro("__UINT16_TYPE__", "unsigned int");
-  Builder.defineMacro("__INT16_TYPE__", "int");
 
   if (!this->CPU.empty()) {
     auto It = llvm::find_if(
         AVRMcus, [&](const MCUInfo &Info) { return Info.Name == this->CPU; });
 
     if (It != std::end(AVRMcus))
       Builder.defineMacro(It->DefineName);
   }
 }

clang/lib/Frontend/InitPreprocessor.cpp

static void DefineExactWidthIntType(TargetInfo::IntType Ty,
   int TypeWidth = TI.getTypeWidth(Ty);
   bool IsSigned = TI.isTypeSigned(Ty);
 
   // Use the target specified int64 type, when appropriate, so that [u]int64_t
   // ends up being defined in terms of the correct type.
   if (TypeWidth == 64)
     Ty = IsSigned ? TI.getInt64Type() : TI.getUInt64Type();
 
+  // Use the target specified int16 type when appropriate. Some MCU targets
+  // (such as AVR) have definition of [u]int16_t to [un]signed int.
+  if (TypeWidth == 16)
+    Ty = IsSigned ? TI.getInt16Type() : TI.getUInt16Type();
+
   const char *Prefix = IsSigned ? "__INT" : "__UINT";
 
   DefineType(Prefix + Twine(TypeWidth) + "_TYPE__", Ty, Builder);
   DefineFmt(Prefix + Twine(TypeWidth), Ty, TI, Builder);
 
   StringRef ConstSuffix(TI.getTypeConstantSuffix(Ty));
   Builder.defineMacro(Prefix + Twine(TypeWidth) + "_C_SUFFIX__", ConstSuffix);
 }