[RFA 0/9] Address space support for x86

[Richard Biener]

On Thu, Oct 8, 2015 at 6:59 AM, Richard Henderson <rth@redhat.com> wrote:
> I started with Armin Rigo's patch, from back in July,
>
>   https://gcc.gnu.org/ml/gcc/2015-07/msg00125.html
>
> but then wound up changing all of it.  To wit:
>
> (1) If we use more sensible defaults for address spaces, we no longer
> require 8 backend functions and 1 new hook.  Indeed, basic support for
> x86 segmentation via address spaces then requires no overriding of any
> hooks.
>
> (2) In order to do anything useful with x86 segmentation, we need to
> acknowledge that the most common usage puts a valid object at %seg:0.
> Which means that we do need a new hook to disable several optimizations.

We could of course simply make all but the default address-space fall
under -fno-delete-null-pointer-check rules...

> (3) I found that usage within glibc really requires a more structured
> address space, one with a known mapping to the generic address space.
> Thus I introduce __seg_tls, which knows that the segment base is also
> stored at %seg:0.
>
> (4) I attempted to convert the entire tls implementation to use __seg_tls.
> I believe this is ultimately the best long-term solution, but I ran into
> a number of problems both generically and in the backend that prevented
> this from being simple.  I've dropped these patches for now.
>
> (5) However, in the process of attempting (4), I found two problems in
> the backend that could affect any use of address spaces: the movabs
> patterns and string expansions.
>
>
> r~
>
>
> Richard Henderson (9):
>   Change default of non-overlapping address space conversion
>   Relax ADDR_SPACE_GENERIC_P checks for default address space hooks
>   i386: Handle address spaces in movabs patterns
>   i386: Disallow address spaces with string insns
>   i386: Add address spaces for fs/gs segments
>   i386: Replace ix86_address_seg with addr_space_t
>   i386: Add address space for tls
>   Add TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID
>   Fix PR 66768
>
>  gcc/config/i386/i386-c.c                     |   8 +
>  gcc/config/i386/i386-protos.h                |   8 +-
>  gcc/config/i386/i386.c                       | 296 +++++++++++++++++++--------
>  gcc/config/i386/i386.h                       |   3 +-
>  gcc/config/i386/i386.md                      |  91 +++++---
>  gcc/config/i386/predicates.md                |   8 +-
>  gcc/config/i386/rdos.h                       |   2 +-
>  gcc/doc/tm.texi                              |   5 +
>  gcc/doc/tm.texi.in                           |   2 +
>  gcc/expr.c                                   |  30 +--
>  gcc/fold-const.c                             |   6 +-
>  gcc/gimple.c                                 |  12 +-
>  gcc/target.def                               |   9 +
>  gcc/targhooks.c                              |  48 ++---
>  gcc/targhooks.h                              |   1 +
>  gcc/testsuite/gcc.target/i386/addr-space-1.c |  11 +
>  gcc/tree-ssa-address.c                       |   2 +-
>  17 files changed, 385 insertions(+), 157 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/i386/addr-space-1.c
>
> --
> 2.4.3
>