Re: [PATCH 0/9] start converting POINTER_SIZE to a hook

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 27/07/15 04:10, tbsaunde+gcc@tbsaunde.org wrote:
> From: Trevor Saunders <tbsaunde+gcc@tbsaunde.org>
> 
> Hi,
> 
> $subject.
> 
> patches individually bootstrapped + regtested on x86_64-linux-gnu, and run
> through config-list.mk with more patches removing usage of the macro.  Ok?
> 
> Trev
> 
> Trevor Saunders (9):
>   remove POINTER_SIZE_UNITS macro
>   add pointer_size target hook
>   target.h: change to use targetm.pointer_size instead of POINTER_SIZE
>   varasm.c: switch from POINTER_SIZE to targetm.pointer_size ()
>   ubsan.c: switch from POINTER_SIZE to targetm.pointer_size ()
>   tree-chkp.c: switch to targetm.pointer_size ()
>   stor-layout.c: switch to targetm.pointer_size ()
>   tree.c: switch to targetm.pointer_size ()
>   emit-rtl.c: switch to targetm.pointer_size ()
> 
>  gcc/c-family/c-cppbuiltin.c |  2 +-
>  gcc/defaults.h              |  3 ---
>  gcc/doc/tm.texi             |  7 +++++++
>  gcc/doc/tm.texi.in          |  2 ++
>  gcc/dwarf2asm.c             |  4 ++--
>  gcc/emit-rtl.c              |  5 +++--
>  gcc/lto/lto-object.c        |  3 ++-
>  gcc/stor-layout.c           |  9 +++++----
>  gcc/target.def              |  8 ++++++++
>  gcc/target.h                |  8 ++++++++
>  gcc/targhooks.c             |  8 ++++++++
>  gcc/targhooks.h             |  1 +
>  gcc/tree-chkp.c             | 14 ++++++++------
>  gcc/tree.c                  |  3 ++-
>  gcc/ubsan.c                 |  3 ++-
>  gcc/varasm.c                | 12 ++++++------
>  16 files changed, 65 insertions(+), 27 deletions(-)
> 

I'm getting a bit worried about the potential performance impact from
all these indirect function call hooks.  This is a good example of when
it's probably somewhat unnecessary.  I doubt that the compiler could
function correctly if this ever changed in the middle of a function.

It would be much better if targetm.pointer_size was a variable that
could be modified by back-end code on those few occasions when that
might be really necessary.

R.