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Re: [PATCH][RFC] Regularize sizetypes
On Thu, 16 Jun 2011, H.J. Lu wrote:
> On Thu, Jun 16, 2011 at 6:09 AM, Richard Guenther <rguenther@suse.de> wrote:
> >
> > For some reason I split out sanitizing sizetypes from the
> > no-undefined-overflow-branch. ?In fact the following patch tries
> > to only fix one thing - make unsigned sizetypes no longer sign-extended.
> >
> > This has (unfortunately) interesting side-effects, and some of them
> > have been mitigated by already committed patches during the last half
> > year. ?The main remaining issue I run into (and that sort-of blocks
> > me from persuing this really really ...) is that there is a lot of
> > code in GCC that assumes it can do modulo arithmetic on HOST_WIDE_INTs
> > for sizetypes (pointers / offsets in general). ?Which happens to
> > be wrong when a HOST_WIDE_INT is wider than sizetype (on -m32 multilib
> > on x86_64 for example). ?It happens to work in almost all cases
> > if we sign-extend from 32bit to 64bit HWI but not when we zero-extend.
> > I'm not exactly sure how to proceeed here, other than adding fixups
> > to various places (as seen in the patch below) and hope to catch
> > all existing errors. ?[yes, I already tried making all sizetypes
> > signed, really signed, but that has loads of fallout as well]
> >
> > That said, the fact that sizetypes are sign-extended has caused
> > wrong-code bugs in the past, and TYPE_UNSIGNED is really used
> > inconsistently. ?So I think this is definitely worth fixing.
> >
> > Eventually a first move would be to (finally) get rid of the
> > requirement of sizetype offset arguments for POINTER_PLUS_EXPR.
> > I didn't yet start on that project though.
> >
> > I remember the following bootstrapped fine on x86_64-unknown-linux-gnu
> > at least for C, with a few remaining regressions. ?I'm trying
> > a full all-lang bootstrap & regtest now.
> >
> > Comments? ?Questions?
>
> Any expected impacts on x32 branch after this changed is merged?
None that I'm aware of. But as I said above I'm not sure it'll be
in mergeable state any time.
Richard.
> > Thanks,
> > Richard.
> >
> > 2011-06-16 ?Richard Guenther ?<rguenther@suse.de>
> >
> > ? ? ? ?* fold-const.c (div_if_zero_remainder): sizetypes no longer
> > ? ? ? ?sign-extend.
> > ? ? ? ?* stor-layout.c (initialize_sizetypes): Likewise.
> > ? ? ? ?* tree-ssa-ccp.c (bit_value_unop_1): Likewise.
> > ? ? ? ?(bit_value_binop_1): Likewise.
> > ? ? ? ?* tree.c (double_int_to_tree): Likewise.
> > ? ? ? ?(double_int_fits_to_tree_p): Likewise.
> > ? ? ? ?(force_fit_type_double): Likewise.
> > ? ? ? ?(host_integerp): Likewise.
> > ? ? ? ?(int_fits_type_p): Likewise.
> > ? ? ? ?* expr.c (get_inner_reference): Sign-extend offset.
> > ? ? ? ?* tree-ssa-structalias.c (get_constraint_for_ptr_offset): Likewise.
> > ? ? ? ?* tree-cfg.c (verify_types_in_gimple_reference): Do not compare
> > ? ? ? ?sizes by pointer.
> >
>
>
--
Richard Guenther <rguenther@suse.de>
Novell / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer