http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50494
--- Comment #32 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2013-03-05
15:32:15 UTC ---
> But in all places I found we check TREE_ASM_WRITTEN on DECL_INITIAL
> of the SYMBOL_REF_DECL ...
Nope, maybe_output_constant_def_contents has:
rtx symbol = XEXP (desc->rtl, 0);
tree exp = desc->value;
if (flag_syntax_only)
return;
if (TREE_ASM_WRITTEN (exp))
/* Already output; don't do it again. */
return;
so the DECL_INITIAL of the SYMBOL_REF_DECL must be desc->value.
> So it must be pure luck that we survived LTO bootstrap before my
> patch (as far as I understand things). Before my patch we created
> yet another decl for the constant pool entry. With my patch
> we will have one less (we still have the decls from the constant
> pool entries that end up being shared in the LTRANS unit).
We use LTO on heavy Ada applications with an unmodified 4.7 compiler (modulo a
patch for -g) so I don't think that luck has anything to do here.
> So in the end I can agree to that my patch doesn't really fix
> the original issue fully. So we can as well revert it and
> instead avoid messing with alignment of the constant pool entries.
That would be my preference.
> Hmm, maybe. Then, why do we copy the constant in the first place ...
>
> Thus,
>
> Index: varasm.c
> ===================================================================
> --- varasm.c (revision 196462)
> +++ varasm.c (working copy)
> @@ -3087,7 +3087,7 @@ build_constant_desc (tree exp, tree decl
> int labelno;
>
> desc = ggc_alloc_constant_descriptor_tree ();
> - desc->value = copy_constant (exp);
> + desc->value = exp;
>
> /* Propagate marked-ness to copied constant. */
> if (flag_mudflap && mf_marked_p (exp))
>
> should be an "equivalent" fix.
This call to copy_constant has been there for ages though. so a little bit of
archeology would probably be in order before removing it.
In the meantime, I've successfully bootstrapped my patchlet so we can also go
for it.
