Re: [PATCH] PR target/67850: Wrong call_used_regs used in aggregate_value_p

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Wed, Oct 7, 2015 at 2:01 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Wed, Oct 7, 2015 at 10:53 AM, Richard Biener <rguenther@suse.de> wrote:
>
>>> >>> > > Since targetm.expand_to_rtl_hook may be called to switch ABI, it should
>>> >>> > > be called for each function before expanding to RTL.  Otherwise, we may
>>> >>> > > use the stale information from compilation of the previous function.
>>> >>> > > aggregate_value_p uses call_used_regs.  aggregate_value_p is used by
>>> >>> > > IPA and return value optimization, which are called before
>>> >>> > > pass_expand::execute after RTL expansion starts.  We need to call
>>> >>> > > targetm.expand_to_rtl_hook early enough in cgraph_node::expand to make
>>> >>> > > sure that everything is in sync when RTL expansion starts.
>>> >>> > >
>>> >>> > > Tested on Linux/x86-64.  OK for trunk?
>>> >>> >
>>> >>> > Hmm, I think set_cfun hook should handle this.  expand_to_rtl_hook shouldn't
>>> >>> > mess with per-function stuff.
>>> >>> >
>>> >>> > Richard.
>>> >>> >
>>> >>>
>>> >>> I am testig this patch.  OK for trunk if there is no regresion?
>>> >>>
>>> >>>
>>> >>> H.J.
>>> >>> --
>>> >>> ix86_maybe_switch_abi is called to late during RTL expansion and we
>>> >>> use the stale information from compilation of the previous function.
>>> >>> aggregate_value_p uses call_used_regs.  aggregate_value_p is used by
>>> >>> IPA and return value optimization, which are called before
>>> >>> pass_expand::execute after RTL expansion starts.  Instead,
>>> >>> ix86_maybe_switch_abi should be merged with ix86_set_current_function.
>>> >>>
>>> >>>       PR target/67850
>>> >>>       * config/i386/i386.c (ix86_set_current_function): Renamed
>>> >>>       to ...
>>> >>>       (ix86_set_current_function_1): This.
>>> >>>       (ix86_set_current_function): New. incorporate old
>>> >>>       ix86_set_current_function and ix86_maybe_switch_abi.
>>> >>>       (ix86_maybe_switch_abi): Removed.
>>> >>>       (TARGET_EXPAND_TO_RTL_HOOK): Likewise.
>>> >>> ---
>>> >>>  gcc/config/i386/i386.c | 33 ++++++++++++++++++---------------
>>> >>>  1 file changed, 18 insertions(+), 15 deletions(-)
>>> >>>
>>> >>> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
>>> >>> index d59b59b..a0adf3d 100644
>>> >>> --- a/gcc/config/i386/i386.c
>>> >>> +++ b/gcc/config/i386/i386.c
>>> >>> @@ -6222,7 +6222,7 @@ ix86_reset_previous_fndecl (void)
>>> >>>     FNDECL.  The argument might be NULL to indicate processing at top
>>> >>>     level, outside of any function scope.  */
>>> >>>  static void
>>> >>> -ix86_set_current_function (tree fndecl)
>>> >>> +ix86_set_current_function_1 (tree fndecl)
>>> >>>  {
>>> >>>    /* Only change the context if the function changes.  This hook is called
>>> >>>       several times in the course of compiling a function, and we don't want to
>>> >>> @@ -6262,6 +6262,23 @@ ix86_set_current_function (tree fndecl)
>>> >>>    ix86_previous_fndecl = fndecl;
>>> >>>  }
>>> >>>
>>> >>> +static void
>>> >>> +ix86_set_current_function (tree fndecl)
>>> >>> +{
>>> >>> +  ix86_set_current_function_1 (fndecl);
>>> >>> +
>>> >>> +  if (!cfun)
>>> >>> +    return;
>>> >>
>>> >> I think you want to test !fndecl here.  Why split this out at all?
>>> >> The ix86_previous_fndecl caching should still work, no?
>>> >>
>>> >>> +  /* 64-bit MS and SYSV ABI have different set of call used registers.
>>> >>> +     Avoid expensive re-initialization of init_regs each time we switch
>>> >>> +     function context since this is needed only during RTL expansion.  */
>>> >>
>>> >> The comment is now wrong (and your bug shows it was wrong previously).
>>> >>
>>> >
>>> > Here is the updated patch.  OK for master if there is no
>>> > regression on Linux/x86-64?
>>> >
>>>
>>> There is no regression.  OK for trunk?
>>
>> Ok with me but I defer to Uros for the approval.
>
> OK for mainline and release branches after a few days.
>

I backported it to GCC 5.  Backporting to 4.9 requires significant
change since ix86_set_current_function has changed since 4.9.
I have no plan to backport it to 4.9.


-- 
H.J.