Re: [PATCH] libgccjit: Add ability to get CPU features

[Antoni Boucher <bouanto@zoho.com>]

David: Ping.
Iain: Ping.

On Tue, 2024-02-13 at 13:37 -0500, Antoni Boucher wrote:
> David: Ping.
> 
> On Tue, 2024-02-06 at 07:54 -0500, Antoni Boucher wrote:
> > David: Ping.
> > 
> > On Tue, 2024-01-30 at 10:50 -0500, Antoni Boucher wrote:
> > > David: I'm unsure what to do here. It seems we cannot find a
> > > reviewer.
> > > Would it help if I show you the code in gccrs that is similar?
> > > Would it help if I ask someone from gccrs to review this code?
> > > 
> > > On Sat, 2024-01-20 at 09:50 -0500, Antoni Boucher wrote:
> > > > CC-ing Iain in case they can do the review since it is based on
> > > > how
> > > > they did it in the D frontend.
> > > > Could you please do the review?
> > > > Thanks!
> > > > 
> > > > On Thu, 2023-11-09 at 18:04 -0500, David Malcolm wrote:
> > > > > On Thu, 2023-11-09 at 17:27 -0500, Antoni Boucher wrote:
> > > > > > Hi.
> > > > > > This patch adds support for getting the CPU features in
> > > > > > libgccjit
> > > > > > (bug
> > > > > > 112466)
> > > > > > 
> > > > > > There's a TODO in the test:
> > > > > > I'm not sure how to test that gcc_jit_target_info_arch
> > > > > > returns
> > > > > > the
> > > > > > correct value since it is dependant on the CPU.
> > > > > > Any idea on how to improve this?
> > > > > > 
> > > > > > Also, I created a CStringHash to be able to have a
> > > > > > std::unordered_set<const char *>. Is there any built-in way
> > > > > > of
> > > > > > doing
> > > > > > this?
> > > > > 
> > > > > Thanks for the patch.
> > > > > 
> > > > > Some high-level questions:
> > > > > 
> > > > > Is this specifically about detecting capabilities of the host
> > > > > that
> > > > > libgccjit is currently running on? or how the target was
> > > > > configured
> > > > > when libgccjit was built?
> > > > > 
> > > > > One of the benefits of libgccjit is that, in theory, we
> > > > > support
> > > > > all
> > > > > of
> > > > > the targets that GCC already supports.  Does this patch
> > > > > change
> > > > > that,
> > > > > or
> > > > > is this more about giving client code the ability to
> > > > > determine
> > > > > capabilities of the specific host being compiled for?
> > > > > 
> > > > > I'm nervous about having per-target jit code.  Presumably
> > > > > there's
> > > > > a
> > > > > reason that we can't reuse existing target logic here - can
> > > > > you
> > > > > please
> > > > > describe what the problem is.  I see that the ChangeLog has:
> > > > > 
> > > > > > 	* config/i386/i386-jit.cc: New file.
> > > > > 
> > > > > where i386-jit.cc has almost 200 lines of nontrivial code. 
> > > > > Where
> > > > > did
> > > > > this come from?  Did you base it on existing code in our
> > > > > source
> > > > > tree,
> > > > > making modifications to fit the new internal API, or did you
> > > > > write
> > > > > it
> > > > > from scratch?  In either case, how onerous would this be for
> > > > > other
> > > > > targets?
> > > > > 
> > > > > I'm not at expert at target hooks (or at the i386 backend),
> > > > > so
> > > > > if
> > > > > we
> > > > > do
> > > > > go with this approach I'd want someone else to review those
> > > > > parts
> > > > > of
> > > > > the patch.
> > > > > 
> > > > > Have you verified that GCC builds with this patch with jit
> > > > > *not*
> > > > > enabled in the enabled languages?
> > > > > 
> > > > > [...snip...]
> > > > > 
> > > > > A nitpick:
> > > > > 
> > > > > > +.. function:: const char * \
> > > > > > +              gcc_jit_target_info_arch
> > > > > > (gcc_jit_target_info
> > > > > > *info)
> > > > > > +
> > > > > > +   Get the architecture of the currently running CPU.
> > > > > 
> > > > > What does this string look like?
> > > > > How long does the pointer remain valid?
> > > > > 
> > > > > Thanks again; hope the above makes sense
> > > > > Dave
> > > > > 
> > > > 
> > > 
> > 
>