Re: [PATCH] libgccjit: Add support for register variables [PR104072]

[David Malcolm <dmalcolm@redhat.com>]

On Sat, 2022-01-22 at 19:29 -0500, Antoni Boucher wrote:
> Hi.
> 
> Le mardi 18 janvier 2022 à 18:49 -0500, David Malcolm a écrit :
> > On Mon, 2022-01-17 at 19:46 -0500, Antoni Boucher via Gcc-patches
> > wrote:
> > > I missed the comment about the new define, so here's the updated
> > > patch.
> > 
> > Thanks for the patch.
> > > 
> > > Le lundi 17 janvier 2022 à 19:24 -0500, Antoni Boucher via Jit a
> > > écrit :
> > > > Hi.
> > > > This patch add supports for register variables in libgccjit.
> > > > 
> > > > It passes the JIT tests, but since I added a function in
> > > > reginfo.c,
> > > > I
> > > > wonder if I should run the whole testsuite.
> > 
> > We're in stage 4 for gcc 12, so we should be especially careful
> > about
> > changes right now, and we're not meant to be adding new GCC 12
> > features.
> > 
> > How close is gcc 12's libgccjit to being usable with your rustc
> > backend?  If we're almost there, I'm willing to make our case for
> > late-
> > breaking libgccjit changes to the release managers, but if you
> > think
> > rustc users are going to need to build a patched libgccjit, then
> > let's
> > queue this up for gcc 13.
> 
> As I mentioned in my other email, if the 4 patches currently being
> reviewed (and listed here:
> https://github.com/antoyo/libgccjit-patches) were included in gcc 12,
> I'd be able to build rustc_codegen_gcc with an unpatched gcc.

Thanks.  Once the relevant patches look good to me, I'll approach the
release managers with the proposal.

> 
> It is to be noted however, that I'll need more patches for future
> work.
> Off the top of my head, I'll at least need a patch for the inline
> attribute, try/catch and target-specific builtins.
> The last 2 features will probably take some time to implement, so
> I'll
> let you judge if you think it's worth merging the 4 patches currently
> being reviewed for gcc 12.

Thanks, though I don't know enough about your project's features to
make the judgement call.  Does rustc_codegen_gcc have releases yet, or
are you just pointing people at the trunk of your repo?  I guess the
question is - are you hoping to be able to point people at distro
installs of gcc 12's libgccjit and have some version of
rustc_codegen_gcc "just work" with that, or are they going to have to
rebuild their own libgccjit to meaningfully use it?

[...snip various corrections...]

> 
> > > diff --git a/gcc/testsuite/jit.dg/test-register-variable.c
> > > b/gcc/testsuite/jit.dg/test-register-variable.c
> > > new file mode 100644
> > > index 00000000000..3cea3f1668f
> > > --- /dev/null
> > > +++ b/gcc/testsuite/jit.dg/test-register-variable.c
> > > +

[...snip...]

> > > +/* { dg-final { jit-verify-output-file-was-created "" } } */
> > > +/* { dg-final { jit-verify-assembler-output "movl      \\\$1,
> > > %r12d" } } */
> > > +/* { dg-final { jit-verify-assembler-output "movl      \\\$2,
> > > %r13d" } } */
> > 
> > How target-specific is this test?
> 
> It will only work on x86-64. Should I feature-gate the test somehow?


Yes; I think you can do this by adding this to the top of the test:

   /* { dg-do compile { target x86_64-*-* } } */

like test-asm.c does.

> > 
> > We should have test coverage for at least these two errors:
> > 
> > - gcc_jit_lvalue_set_register_name(global_variable,
> > "this_is_not_a_register");
> > - attempting to set the name for a var that doesn't fit in the
> > given
> > register (e.g. trying to use a register for an array that's way too
> > big)
> 
> Done.

Thanks.

Is the updated patch available for review? It looks like you didn't
attach it.

Dave