[PATCH] RISC-V: Implment __builtin_thread_pointer

[Kito Cheng]

On Thu, Jul 9, 2020 at 4:03 AM Jim Wilson <jimw@sifive.com> wrote:
>
> On Tue, Jul 7, 2020 at 2:52 AM Kito Cheng <kito.cheng@sifive.com> wrote:
> > gcc/ChangeLog:
> >         * gcc/config/riscv/riscv.md (): New.
> >         (TP_REGNUM): Ditto.
> >         * doc/extend.texi (Target Builtins): Add RISC-V built-in section.
> >         Document __builtin_thread_pointer.
> > gcc/testsuite/ChangeLog:
> >         * gcc.target/riscv/read-thread-pointer.c: New.
>
> It looks OK to me in general.
>
> You added builtin_thread_pointer but not builtin_set_thread_pointer.
> Maybe we should implement both as long as we are implementing one?  If
> clang only implements one, maybe it should implement the other also?
> This doesn't have to be part of this patch.  This could be a separate
> issue.

LLVM side only implements builtin_thread_pointer at this moment,
and I also saw the gcc and only half target are implemented both,
so I only implement builtin_thread_pointer first, but I think it's good idea
to implement both.

> The builtin_thread_pointer docs looks out-of-date.  It is documented
> for alpha and SH, but it is implemented in gcc/builtins.c not in the
> backends.  A scan of md files show that quite a few targets support it
> but don't document it.  I think it should be documented in the generic
> builtins section not in the target dependent builtins sections with
> some language that says not all targets support it.  This doesn't have
> to be part of this patch.  This could be a separate issue.

Yeah, I've found the issue when I seeking the writing material for the doc :P


> We have two existing undocumented builtins.  __builtin_riscv_fsflags
> and __builtin_riscv_frflags for setting or reading the FP flags.  I
> don't know if anyone uses them though.  newlib and glbic both use
> extended asms for these operations.  This doesn't have to be part of
> this patch.  This could be a separate issue.

Got it.

> There is a document https://github.com/riscv/riscv-c-api-doc for
> coordinating gcc and llvm work that has an empty list of builtin
> functions.  I'm not sure if this document is still useful.  If this is
> a RISC-V specific builtin then it should be listed here, but I don't
> think it should be considered a RISC-V specific builtin.  There is an
> unresolved pull request for the frflags and fsflags builtins.  I guess
> I forgot about that.

Oh...I even forgot the PR was opened by me...

>
> Jim