To POD or not to POD

[Iain Buclaw]

On 13 February 2013 14:35, Johannes Pfau <nospam at example.com> wrote:

> Am Wed, 13 Feb 2013 14:10:26 +0000
> schrieb Iain Buclaw <ibuclaw at ubuntu.com>:
>
> > On 13 February 2013 13:26, Johannes Pfau <nospam at example.com> wrote:
> >
> > > Am Tue, 12 Feb 2013 18:16:31 +0000
> > > schrieb Iain Buclaw <ibuclaw at ubuntu.com>:
> > >
> > > > TREE_ADDRESSABLE should be sufficient.  I can't think any reason
> > > > off the top of my head why not.
> > > >
> > >
> > > maybe TREE_ADDRESSABLE is too strong: It generates errors in the
> > > backend if the frontend produces non-lvalues:
> > > ---
> > >     auto b = Date();
> > >     a(b);
> > > ---
> > >
> > > works, but
> > > ---
> > >     a(Date());
> > > ---
> > >
> > > fails in gimplify.c. Do we really have to rewrite such cases so that
> > > non-PODs get a temporary variable? And how would this be done? It
> > > seems we would have to use the frontend for this, as maybeMakeTemp
> > > and makeTemp refuse to work for TREE_ADDRESSABLE types.
> > >
> >
> > Don't set it on the variable, set it on the type.
> >
> > TypeStruct::toCtype()
> > {
> >     TYPE_ADDRESSABLE(ctype) = !isPOD();
> > }
>
> That's actually what I did. But the backend wants to create a copy of
> the Date type which then fails as create_tmp_var fails for
> TREE_ADDRESSABLE types.
>
> Complete test case:
> https://gist.github.com/jpf91/4944999
>
> -----
>
> ../../objdir-4.7/x86_64-unknown-linux-gnu/libphobos/dm-test.reduced/datetime2.d:22:
> internal compiler error: in create_tmp_var, at gimplify.c:479 0x804509
> -----
>
>

Ahh, that's because of this piece of codegen:

SAVE_EXPR <*test.Date.this (&((void) (__ctmp971 = _D4test4Date6__initZ);,
__ctmp971), 0)>


Gimple doesn't like the dereference in SAVE_EXPR.  This should work.

tree
IRState::makeTemp (tree t)
{
  tree type = TREE_TYPE (t);
  if (TREE_CODE (type) != ARRAY_TYPE && !TREE_ADDRESSABLE (type))
    return save_expr (t);

  return stabilize_reference (t);
}


So the generated code is now:

*SAVE_EXPR <test.Date.this (&((void) (__ctmp971 = _D4test4Date6__initZ);,
__ctmp971), 0)>



Regards
-- 
Iain Buclaw

*(p < e ? p++ : p) = (c & 0x0f) + '0';
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