Re: [PATCH] libgccjit: Handle truncation and extension for casts [PR 95498]

[David Malcolm <dmalcolm@redhat.com>]

On Fri, 2021-06-18 at 16:42 -0400, Antoni Boucher wrote:
> I'm sending the patch once again for review.
> 
> As it's the first time I'll land a patch, I'm not sure what needs to be
> done when it's approved.
> Do I just commit it to the master branch directly?

Commit (and push), yes, but...

Please ensure the subject line of the commit matches our policy:

"libgccjit: Handle truncation and extension for casts [PR95498]"

is a good subject, whereas:

"This patch handles truncation and extension for casts in jit."

is not.

We have some hooks that will only accept pushes if the commit message
has a correctly formatted ChangeLog.  The hooks ought to also add
notification comments to bugzilla for any bugs mentioned in the commit
message.

See https://gcc.gnu.org/gitwrite.html#checkin


FWIW in my own workflow I have a writable working copy that I keep for
just doing pushes; 
I do a
  git pull
verify the build, then
  git am FOO.patch --ignore-date
to apply the patch that was tested and approved, then do a last test
with that, then
  git push

That way I only push the patches that I've tested and have been
approved, and the other ones are in an entirely separate working copy.
This may be overkill though.

I'm also on #gcc IRC right now on OFTC (dmalcolm) if you run into
issues.

Dave

> 
> Thanks!
> 
> Le vendredi 11 juin 2021 à 13:49 -0400, David Malcolm a écrit :
> > On Thu, 2021-05-27 at 21:22 -0400, Antoni Boucher wrote:
> > > Here's the patch with the condition removed.
> > > I believe everything is now fixed.
> > > Thanks!
> > 
> > Thanks; this looks good to me.  Is this the latest version of the
> > patch; would you like me to apply it?
> > 
> > Dave
> > 
> > > 
> > > Le jeudi 27 mai 2021 à 18:21 -0400, David Malcolm a écrit :
> > > > On Tue, 2021-05-25 at 20:16 -0400, Antoni Boucher wrote:
> > > > > I updated the patch according to the comments by Tom Tromey.
> > > > > 
> > > > > There's one question left about your question regarding
> > > > > C_MAYBE_CONST_EXPR, David:
> > > > > 
> > > > > I am not sure if we can get a C_MAYBE_CONST_EXPR from
> > > > > libgccjit,
> > > > > and
> > > > > it
> > > > > indeed seems like it's only created in c-family.
> > > > > However, we do use it in libgccjit here:
> > > > > https://github.com/gcc-mirror/gcc/blob/master/gcc/jit/jit-playback.c#L1180
> > > > > 
> > > > > I tried removing the condition `if (TREE_CODE (t_ret) !=
> > > > > C_MAYBE_CONST_EXPR)` and all the tests of libgccjit still pass.
> > > > > 
> > > > > That code was copied from here:
> > > > > https://github.com/gcc-mirror/gcc/blob/master/gcc/c/c-convert.c#L175
> > > > > and might not be needed in libgccjit.
> > > > > 
> > > > > Should I just remove the condition, then?
> > > > 
> > > > I think so.
> > > > 
> > > > Thanks
> > > > Dave
> > > > 
> > > > > 
> > > > > Le jeudi 13 mai 2021 à 19:58 -0400, David Malcolm a écrit :
> > > > > > On Thu, 2021-05-13 at 19:31 -0400, Antoni Boucher wrote:
> > > > > > > Thanks for your answer.
> > > > > > > 
> > > > > > > See my answers below:
> > > > > > > 
> > > > > > > Le jeudi 13 mai 2021 à 18:13 -0400, David Malcolm a écrit :
> > > > > > > > On Sat, 2021-02-20 at 17:17 -0500, Antoni Boucher via
> > > > > > > > Gcc-
> > > > > > > > patches
> > > > > > > > wrote:
> > > > > > > > > Hi.
> > > > > > > > > Thanks for your feedback!
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > Sorry about the delay in responding.
> > > > > > > > 
> > > > > > > > In the past I was hesitant about adding more cast support
> > > > > > > > to
> > > > > > > > libgccjit
> > > > > > > > since I felt that the user could always just create a
> > > > > > > > union
> > > > > > > > to
> > > > > > > > do
> > > > > > > > the
> > > > > > > > cast.  Then I tried actually using the libgccjit API to
> > > > > > > > do
> > > > > > > > this,
> > > > > > > > and
> > > > > > > > realized how much work it adds, so I now think we do want
> > > > > > > > to
> > > > > > > > support
> > > > > > > > casting more types.
> > > > > > > > 
> > > > > > > > 
> > > > > > > > > See answers below:
> > > > > > > > > 
> > > > > > > > > On Sat, Feb 20, 2021 at 11:20:35AM -0700, Tom Tromey
> > > > > > > > > wrote:
> > > > > > > > > > > > > > > "Antoni" == Antoni Boucher via Gcc-patches
> > > > > > > > > > > > > > > <   
> > > > > > > > > > > > > > > gcc-patches@gcc.gnu.org> writes:
> > > > > > > > > > 
> > > > > > > > > > Antoni> gcc/jit/
> > > > > > > > > > Antoni>         PR target/95498
> > > > > > > > > > Antoni>         * jit-playback.c: Add support to
> > > > > > > > > > handle
> > > > > > > > > > truncation
> > > > > > > > > > and extension
> > > > > > > > > > Antoni>         in the convert function.
> > > > > > > > > > 
> > > > > > > > > > Antoni> +  switch (dst_code)
> > > > > > > > > > Antoni> +    {
> > > > > > > > > > Antoni> +    case INTEGER_TYPE:
> > > > > > > > > > Antoni> +    case ENUMERAL_TYPE:
> > > > > > > > > > Antoni> +      t_ret = convert_to_integer (dst_type,
> > > > > > > > > > expr);
> > > > > > > > > > Antoni> +      goto maybe_fold;
> > > > > > > > > > Antoni> +
> > > > > > > > > > Antoni> +    default:
> > > > > > > > > > Antoni> +      gcc_assert
> > > > > > > > > > (gcc::jit::active_playback_ctxt);
> > > > > > > > > > Antoni> +      gcc::jit::active_playback_ctxt-
> > > > > > > > > > > add_error
> > > > > > > > > > (NULL,
> > > > > > > > > > "unhandled conversion");
> > > > > > > > > > Antoni> +      fprintf (stderr, "input
> > > > > > > > > > expression:\n");
> > > > > > > > > > Antoni> +      debug_tree (expr);
> > > > > > > > > > Antoni> +      fprintf (stderr, "requested type:\n");
> > > > > > > > > > Antoni> +      debug_tree (dst_type);
> > > > > > > > > > Antoni> +      return error_mark_node;
> > > > > > > > > > Antoni> +
> > > > > > > > > > Antoni> +    maybe_fold:
> > > > > > > > > > Antoni> +      if (TREE_CODE (t_ret) !=
> > > > > > > > > > C_MAYBE_CONST_EXPR)
> > > > > > > > 
> > > > > > > > Do we even get C_MAYBE_CONST_EXPR in libgccjit?  That
> > > > > > > > tree
> > > > > > > > code
> > > > > > > > is
> > > > > > > > defined in c-family/c-common.def; how can nodes of that
> > > > > > > > kind
> > > > > > > > be
> > > > > > > > created
> > > > > > > > outside of the c-family?
> > > > > > > 
> > > > > > > I am not sure, but that seems like it's only created in c-
> > > > > > > family
> > > > > > > indeed.
> > > > > > > However, we do use it in libgccjit here:
> > > > > > > 
> > > > > > > https://github.com/gcc-mirror/gcc/blob/master/gcc/jit/jit-playback.c#L1180
> > > > > > > 
> > > > > > > > 
> > > > > > > > > > Antoni> +       t_ret = fold (t_ret);
> > > > > > > > > > Antoni> +      return t_ret;
> > > > > > > > > > 
> > > > > > > > > > It seems weird to have a single 'goto' to maybe_fold,
> > > > > > > > > > especially
> > > > > > > > > > inside
> > > > > > > > > > a switch like this.
> > > > > > > > > > 
> > > > > > > > > > If you think the maybe_fold code won't be reused,
> > > > > > > > > > then
> > > > > > > > > > it
> > > > > > > > > > should
> > > > > > > > > > just
> > > > > > > > > > be
> > > > > > > > > > hoisted up and the 'goto' removed.
> > > > > > > > > 
> > > > > > > > > This actually depends on how the support for cast
> > > > > > > > > between
> > > > > > > > > integers
> > > > > > > > > and 
> > > > > > > > > pointers will be implemented (see below).
> > > > > > > > > If we will support truncating pointers (does that even
> > > > > > > > > make
> > > > > > > > > sense?
> > > > > > > > > and
> > > > > > > > > I 
> > > > > > > > > guess we cannot extend a pointer unless we add the
> > > > > > > > > support
> > > > > > > > > for 
> > > > > > > > > uint128_t), that label will be reused for that case.
> > > > > > > > > Otherwise, it might not be reused.
> > > > > > > > > 
> > > > > > > > > So, please tell me which option to choose and I'll
> > > > > > > > > update
> > > > > > > > > my
> > > > > > > > > patch.
> > > > > > > > 
> > > > > > > > FWIW I don't think we'll want to support truncating or
> > > > > > > > extending
> > > > > > > > pointers.
> > > > > > > 
> > > > > > > Ok, but do you think we'll want to support casts between
> > > > > > > integers
> > > > > > > and
> > > > > > > pointers?
> > > > > > 
> > > > > > Yes, though we probably want to reject truncating a pointer
> > > > > > into
> > > > > > a
> > > > > > smaller integer type.
> > > > > > 
> > > > > > > I opened an issue about this
> > > > > > > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95438) and
> > > > > > > would
> > > > > > > be
> > > > > > > willing to do a patch for it eventually.
> > > > > > > 
> > > > > > > > > 
> > > > > > > > > > On the other hand, if the maybe_fold code might be
> > > > > > > > > > reused
> > > > > > > > > > for
> > > > > > > > > > some
> > > > > > > > > > other
> > > > > > > > > > case, then I suppose I would have the case end with
> > > > > > > > > > 'break'
> > > > > > > > > > and
> > > > > > > > > > then
> > > > > > > > > > have this code outside the switch.
> > > > > > > > > > 
> > > > > > > > > > 
> > > > > > > > > > In another message, you wrote:
> > > > > > > > > > 
> > > > > > > > > > Antoni> For your question, the current code already
> > > > > > > > > > works
> > > > > > > > > > with
> > > > > > > > > > boolean and
> > > > > > > > > > Antoni> reals and casts between integers and pointers
> > > > > > > > > > is
> > > > > > > > > > currently
> > > > > > > > > > not
> > > > > > > > > > Antoni> supported.
> > > > > > > > > > 
> > > > > > > > > > I am curious why this wasn't supported.  It seems
> > > > > > > > > > like
> > > > > > > > > > something
> > > > > > > > > > that
> > > > > > > > > > one might want to do.
> > > > > > > > > 
> > > > > > > > > I have no idea as this is my first contribution to gcc.
> > > > > > > > > But this would be indeed very useful and I opened an
> > > > > > > > > issue
> > > > > > > > > about
> > > > > > > > > this: 
> > > > > > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95438
> > > > > > > > > 
> > > > > > > > > > thanks,
> > > > > > > > > > Tom
> > > > > > > > > 
> > > > > > > > > Thanks!
> > > > > > > > > 
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