[PATCH v3] RISC-V: Add .bfloat16 directive

[Kito Cheng]

ping

On Mon, Jan 20, 2025 at 7:25 PM Kito Cheng <kito.cheng@sifive.com> wrote:
>
> RISC-V already support bfloat16 instruciton like Zfbfmin, Zvfbfmin and
> Zvfbfwma, so I think it's reasonable to add .bfloat16 directive to
> support bfloat16 data type.
>
> And the code logic mostly support by common code already.
>
> Changes from v2:
> - Add 'B' to FLT_CHARS this time...
> - Use 'B' in the testcase.
>
> Changes from v1:
> - Add big endian and little endian testcase.
> - Add 'B' to FLT_CHARS.
> - Drop wrong comment in testcase.
> ---
>  gas/config/tc-riscv.c                 |  3 ++-
>  gas/doc/c-riscv.texi                  | 10 ++++++++++
>  gas/testsuite/gas/riscv/bfloat16-be.d | 10 ++++++++++
>  gas/testsuite/gas/riscv/bfloat16-le.d | 10 ++++++++++
>  gas/testsuite/gas/riscv/bfloat16.s    | 21 +++++++++++++++++++++
>  5 files changed, 53 insertions(+), 1 deletion(-)
>  create mode 100644 gas/testsuite/gas/riscv/bfloat16-be.d
>  create mode 100644 gas/testsuite/gas/riscv/bfloat16-le.d
>  create mode 100644 gas/testsuite/gas/riscv/bfloat16.s
>
> diff --git a/gas/config/tc-riscv.c b/gas/config/tc-riscv.c
> index 1a32f4ee57f..344339d87c1 100644
> --- a/gas/config/tc-riscv.c
> +++ b/gas/config/tc-riscv.c
> @@ -473,7 +473,7 @@ const char EXP_CHARS[] = "eE";
>
>  /* Chars that mean this number is a floating point constant.
>     As in 0f12.456 or 0d1.2345e12.  */
> -const char FLT_CHARS[] = "rRsSfFdDxXpPhH";
> +const char FLT_CHARS[] = "rRsSfFdDxXpPhHbB";
>
>  /* Indicate ELF attributes are explicitly set.  */
>  static bool explicit_attr = false;
> @@ -5890,6 +5890,7 @@ static const pseudo_typeS riscv_pseudo_table[] =
>    {"attribute", s_riscv_attribute, 0},
>    {"variant_cc", s_variant_cc, 0},
>    {"float16", float_cons, 'h'},
> +  {"bfloat16", float_cons, 'b'},
>
>    { NULL, NULL, 0 },
>  };
> diff --git a/gas/doc/c-riscv.texi b/gas/doc/c-riscv.texi
> index d2e47455e7c..be3a09487f1 100644
> --- a/gas/doc/c-riscv.texi
> +++ b/gas/doc/c-riscv.texi
> @@ -255,6 +255,16 @@ The @var{tag} is either an attribute number, or one of the following:
>  @code{Tag_RISCV_unaligned_access}, @code{Tag_RISCV_priv_spec},
>  @code{Tag_RISCV_priv_spec_minor}, @code{Tag_RISCV_priv_spec_revision}.
>
> +@cindex @code{.bfloat16} directive, RISC-V
> +@item .bfloat16 @var{value}
> +Floating point constructors for the bfloat16 type, example usage:
> +
> +@smallexample
> +       .bfloat16 12.0
> +       .bfloat16 NaN
> +       .bfloat16 0b:ffc1
> +@end smallexample
> +
>  @end table
>
>  @node RISC-V-Modifiers
> diff --git a/gas/testsuite/gas/riscv/bfloat16-be.d b/gas/testsuite/gas/riscv/bfloat16-be.d
> new file mode 100644
> index 00000000000..21408d0befb
> --- /dev/null
> +++ b/gas/testsuite/gas/riscv/bfloat16-be.d
> @@ -0,0 +1,10 @@
> +# source: bfloat16.s
> +# objdump: -sj .data
> +# as: -mbig-endian
> +
> +.*:[   ]+file format .*
> +
> +Contents of section \.data:
> + 0000 41403dfc 000042f7 8000c2f7 7fff7f80.*
> + 0010 ff807f7f ff7f0080 80800001 8001007f.*
> + 0020 807f3f80 bf804000 c000ffc1 ff81.*
> diff --git a/gas/testsuite/gas/riscv/bfloat16-le.d b/gas/testsuite/gas/riscv/bfloat16-le.d
> new file mode 100644
> index 00000000000..2043a9c161e
> --- /dev/null
> +++ b/gas/testsuite/gas/riscv/bfloat16-le.d
> @@ -0,0 +1,10 @@
> +# source: bfloat16.s
> +# objdump: -sj .data
> +# as: -mlittle-endian
> +
> +.*:[   ]+file format .*
> +
> +Contents of section \.data:
> + 0000 4041fc3d 0000f742 0080f7c2 ff7f807f.*
> + 0010 80ff7f7f 7fff8000 80800100 01807f00.*
> + 0020 7f80803f 80bf0040 00c0c1ff 81ff.*
> diff --git a/gas/testsuite/gas/riscv/bfloat16.s b/gas/testsuite/gas/riscv/bfloat16.s
> new file mode 100644
> index 00000000000..ed92856ff4b
> --- /dev/null
> +++ b/gas/testsuite/gas/riscv/bfloat16.s
> @@ -0,0 +1,21 @@
> + .data
> +       .bfloat16 12.0
> +       .bfloat16 0.123
> +       .bfloat16 +0.0
> +       .bfloat16 123.4
> +       .bfloat16 -0.0
> +       .bfloat16 -123.4
> +       .bfloat16 NaN
> +       .bfloat16 Inf
> +       .bfloat16 -Inf
> +       .bfloat16 3.390e+38
> +       .bfloat16 -3.390e+38
> +       .bfloat16 1.175e-38
> +       .bfloat16 -1.175e-38
> +       .bfloat16 9.194e-41
> +       .bfloat16 -9.194e-41
> +       .bfloat16 1.167e-38
> +       .bfloat16 -1.167e-38
> +       .bfloat16 1.0, -1, 2.0, -2
> +       .bfloat16 0b:ffc1
> +       .bfloat16 0B:ff81
> --
> 2.34.1
>