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

[Antoni Boucher <bouanto@zoho.com>]

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
> > 
>