To POD or not to POD

[Iain Buclaw]

On 13 February 2013 15:20, Iain Buclaw <ibuclaw at ubuntu.com> wrote:

> 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)>
>
>
After some more playing about, David's suggestion would be the quickest. ;-)

-- 
Iain Buclaw

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