Merge pull request #367 from asb/bf16

Add ABI information for __bf16

Author: kito-cheng

riscv-cc.adoc

@@ -449,6 +449,7 @@ alignments (based on the ILP32 convention):
 | long                 |  4            |  4
 | long long            |  8            |  8
 | void *               |  4            |  4
+| +++__bf16+++         |  2            |  2
 | _Float16             |  2            |  2
 | float                |  4            |  4
 | double               |  8            |  8
@@ -475,6 +476,7 @@ alignments (based on the LP64 convention):
 | long long            |  8            |  8
 | +++__int128+++       | 16            | 16
 | void *               |  8            |  8
+| +++__bf16+++         |  2            |  2
 | _Float16             |  2            |  2
 | float                |  4            |  4
 | double               |  8            |  8
@@ -502,6 +504,8 @@ A null pointer (for all types) has the value zero.
 
 `_Float16` is as defined in the C ISO/IEC TS 18661-3 extension.
 
+`__bf16` has the same parameter passing and return rules as for `_Float16`.
+
 `_Complex` types have the same layout as a struct containing two fields of the
 corresponding real type (`float`, `double`, or `long double`), with the first
 member holding the real part and the second member holding the imaginary part.

riscv-elf.adoc

@@ -145,7 +145,8 @@ the _Itanium {Cpp} ABI_ <<itanium-cxx-abi>>;
 there are no RISC-V specific mangling rules.
 
 See the "Type encodings" section in _Itanium {Cpp} ABI_
-for more detail on how to mangle types.
+for more detail on how to mangle types. Note that `__bf16` is mangled in the
+same way as `std::bfloat16_t`.
 
 == ELF Object Files