LoongArch: Add built-in functions description of LoongArch BASE instruction set instructions.

  gcc/ChangeLog:

	* doc/extend.texi: Add section for LoongArch BASE Built-in functions.
---
 gcc/doc/extend.texi | 89 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)
  

On Thu, 2023-04-06 at 16:19 +0800, Lulu Cheng wrote:
> gcc/ChangeLog:
> 
>         * doc/extend.texi: Add section for LoongArch BASE Built-in functions.
> ---
>  gcc/doc/extend.texi | 89 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 89 insertions(+)
> 
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 3adb67aa47a..417af6c368d 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -14669,6 +14669,7 @@ instructions, but allow the compiler to schedule those calls.
>  * Blackfin Built-in Functions::
>  * BPF Built-in Functions::
>  * FR-V Built-in Functions::
> +* LoongArch BASE Built-in Functions::

"Base" instead of "BASE"?

>  * MIPS DSP Built-in Functions::
>  * MIPS Paired-Single Support::
>  * MIPS Loongson Built-in Functions::
> @@ -16197,6 +16198,94 @@ Use the @code{nldub} instruction to load the contents of address @var{x}
>  into the data cache.  The instruction is issued in slot I1@.
>  @end table
>  
> +@node LoongArch BASE Built-in Functions
> +@subsection LoongArch BASE Built-in Functions
> +
> +These built-in functions are available for LoongArch.
> +
> +@itemize
> +@item @code{imm0_31}, an integer literal in range 0 to 31;
> +@item @code{imm0_16383}, an integer literal in range 0 to 16383;
> +@item @code{imm0_32767}, an integer literal in range 0 to 32767;
> +@item @code{imm_n2048_2047}, an integer literal in range -2048 to 2047;

Maybe "compile-time constant" instead of "literal".  Things like
__builtin_loongarch_syscall(42 + 47) is valid, and even

int x = 42;
__builtin_loongarch_syscall(x);

is valid with -O1 or above.

> +@item @code{i8, u8, i16, u16, i32, u32, i64, u64, __drdtime_t, __rdtime_t} are included

"are defined" instead of "are included".

> +in @code{larchintrin.h} and defined as follows:
> +@end itemize
> +
> +@smallexample
> +     typedef char i8;
> +     typedef unsigned char u8;
> +     typedef short i16;
> +     typedef unsigned short u16;
> +     typedef int i32;
> +     typedef unsigned int u32;
> +#if __LONG_MAX__ == __LONG_LONG_MAX__
> +     typedef long int i64;
> +     typedef unsigned long int u64;
> +#else
> +     typedef long long i64;
> +     typedef unsigned long long u64;
> +#endif

This looks nasty.  Maybe just some text description like "i8 is a 8-bit
signed integer type".

> +
> +     typedef struct drdtime@{
> +            unsigned long dvalue;
> +            unsigned long dtimeid;
> +     @} __drdtime_t;
> +
> +     typedef struct rdtime@{
> +            unsigned int value;
> +            unsigned int timeid;
> +     @} __rdtime_t;
> +@end smallexample
> +
> +The intrinsics provided are listed below; each is named after the
> +machine instruction.

This section is documenting built-in functions, so it's better to list
__builtin_loongarch_rdtime_d etc. below, and add a paragraph explaining
the alternative names available via larchintrin.h.

> +
> +@smallexample
> +    __drdtime_t __rdtime_d (void)
> +    __rdtime_t  __rdtimel_w (void)
> +    __rdtime_t  __rdtimeh_w (void)
> +    u32  __movfcsr2gr (imm0_31)
> +    void __movgr2fcsr (imm0_32, u32)
> +    void __cacop_d (imm0_31, u64, imm_n2048_2047)
> +    u32  __cpucfg (u32)
> +    void __asrtle_d (i64, i64)
> +    void __asrtgt_d (i64, i64)
> +    i64  __lddir_d (i64, imm0_31)
> +    void __ldpte_d (i64, imm0_31)
> +
> +    i32  __crc_w_b_w (i8, i32)
> +    i32  __crc_w_h_w (i16, i32)
> +    i32  __crc_w_w_w (i32, i32)
> +    i32  __crc_w_d_w (i64, i32)
> +    i32  __crcc_w_b_w (i8, i32)
> +    i32  __crcc_w_h_w (i16, i32)
> +    i32  __crcc_w_w_w (i32, i32)
> +    i32  __crcc_w_d_w (i64, i32)
> +
> +    u32  __csrrd_w (imm0_16383)
> +    u32  __csrwr_w (u32, imm0_16383)
> +    u32  __csrxchg_w (u32, u32, imm0_16383)
> +    u64  __csrrd_d (imm0_16383)
> +    u64  __csrwr_d (u64, imm0_16383)
> +    u64  __csrxchg_d (u64, u64, imm0_16383)
> +
> +    u8   __iocsrrd_b (u32)
> +    u16  __iocsrrd_h (u32)
> +    u32  __iocsrrd_w (u32)
> +    u64  __iocsrrd_d (u32)
> +    void __iocsrwr_b (u8, u32)
> +    void __iocsrwr_h (u16, u32)
> +    void __iocsrwr_w (u32, u32)
> +    void __iocsrwr_d (u64, u32)
> +
> +    void __dbar (imm0_32767)
> +    void __ibar (imm0_32767)
> +
> +    void __syscall (imm0_32767)
> +    void __break (imm0_32767)
> +@end smallexample
> +
>  @node MIPS DSP Built-in Functions
>  @subsection MIPS DSP Built-in Functions
>