Re: [PATCH 10/52] jit: Replace uses of {FLOAT,{,LONG_}DOUBLE}_TYPE_SIZE

[David Malcolm <dmalcolm@redhat.com>]

On Fri, 2024-06-14 at 10:16 +0800, Kewen.Lin wrote:
> Hi David,
> 
> on 2024/6/13 21:44, David Malcolm wrote:
> > On Sun, 2024-06-02 at 22:01 -0500, Kewen Lin wrote:
> > > Joseph pointed out "floating types should have their mode,
> > > not a poorly defined precision value" in the discussion[1],
> > > as he and Richi suggested, the existing macros
> > > {FLOAT,{,LONG_}DOUBLE}_TYPE_SIZE will be replaced with a
> > > hook mode_for_floating_type.  Unlike the other FEs, for the
> > > uses in recording::memento_of_get_type::get_size, since
> > > {float,{,long_}double}_type_node haven't been initialized
> > > yet, this is to replace {FLOAT,{,LONG_}DOUBLE}_TYPE_SIZE
> > > with calling hook targetm.c.mode_for_floating_type.
> > > 
> > > [1]
> > > https://gcc.gnu.org/pipermail/gcc-patches/2024-May/651209.html
> > > 
> > > gcc/jit/ChangeLog:
> > > 
> > >         * jit-recording.cc
> > > (recording::memento_of_get_type::get_size): Update
> > >         macros {FLOAT,DOUBLE,LONG_DOUBLE}_TYPE_SIZE by calling
> > >         targetm.c.mode_for_floating_type with
> > >         TI_{FLOAT,DOUBLE,LONG_DOUBLE}_TYPE.
> > > ---
> > >  gcc/jit/jit-recording.cc | 12 ++++++++----
> > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/gcc/jit/jit-recording.cc b/gcc/jit/jit-recording.cc
> > > index 68a2e860c1f..7719b898e57 100644
> > > --- a/gcc/jit/jit-recording.cc
> > > +++ b/gcc/jit/jit-recording.cc
> > > @@ -21,7 +21,7 @@ along with GCC; see the file COPYING3.  If not
> > > see
> > >  #include "config.h"
> > >  #include "system.h"
> > >  #include "coretypes.h"
> > > -#include "tm.h"
> > > +#include "target.h"
> > >  #include "pretty-print.h"
> > >  #include "toplev.h"
> > >  
> > > @@ -2353,6 +2353,7 @@ size_t
> > >  recording::memento_of_get_type::get_size ()
> > >  {
> > >    int size;
> > > +  machine_mode m;
> > >    switch (m_kind)
> > >      {
> > >      case GCC_JIT_TYPE_VOID:
> > > @@ -2399,13 +2400,16 @@ recording::memento_of_get_type::get_size
> > > ()
> > >        size = 128;
> > >        break;
> > >      case GCC_JIT_TYPE_FLOAT:
> > > -      size = FLOAT_TYPE_SIZE;
> > > +      m = targetm.c.mode_for_floating_type (TI_FLOAT_TYPE);
> > > +      size = GET_MODE_PRECISION (m).to_constant ();
> > >        break;
> > >      case GCC_JIT_TYPE_DOUBLE:
> > > -      size = DOUBLE_TYPE_SIZE;
> > > +      m = targetm.c.mode_for_floating_type (TI_DOUBLE_TYPE);
> > > +      size = GET_MODE_PRECISION (m).to_constant ();
> > >        break;
> > >      case GCC_JIT_TYPE_LONG_DOUBLE:
> > > -      size = LONG_DOUBLE_TYPE_SIZE;
> > > +      m = targetm.c.mode_for_floating_type
> > > (TI_LONG_DOUBLE_TYPE);
> > > +      size = GET_MODE_PRECISION (m).to_constant ();
> > >        break;
> > >      case GCC_JIT_TYPE_SIZE_T:
> > >        size = MAX_BITS_PER_WORD;
> > 
> > [CCing jit mailing list]
> > 
> > Thanks for the patch; sorry for the delay in responding.
> > 
> > Did your testing include jit?  Note that --enable-languages=all
> > does
> > *not* include it (due to it needing --enable-host-shared).
> 
> Thanks for the hints!  Yes, as noted in the cover letter, I did test
> jit.
> Initially I used TYPE_PRECISION ({float,{long_,}double_type_node) to
> replace these just like what I proposed for the other FE changes, but
> the
> testing showed some failures on test-combination.c etc., by looking
> into
> them, I realized that this call
> recording::memento_of_get_type::get_size
> can happen before when we set up those type nodes.  Then I had to use
> the
> current approach with the new hook, it made all failures gone (no
> regressions).  btw, test result comparison showed some more lines
> with
> "NA->PASS: test-threads.c.exe", since it's positive, I didn't look
> into
> it.
> 
> > 
> > The jit::recording code runs *very* early - before toplev::main. 
> > For
> > example, a call to gcc_jit_type_get_size can trigger the above code
> > path before toplev::main has run.
> > 
> > target.h says each target should have a:
> > 
> >   struct gcc_target targetm = TARGET_INITIALIZER;
> > 
> > Has targetm.c.mode_for_floating_type been initialized enough by
> > that
> > static initialization?  
> 
> It depends on how to define "enough".  The hook has been initialized
> as you pointed out, I just debugged it and confirmed target specific
> hook was called as expected (rs6000_c_mode_for_floating_type on
> Power)
> when this jit::recording function gets called.  If "enough" refers to
> something like command line options, it's not ready.
> 
> > Could the mode_for_floating_type hook be
> > relying on some target-specific dynamic initialization that hasn't
> > run
> > yet?  (e.g. taking account of command-line options?)
> > 
> 
> Yes, it could.  Like rs6000 port, the hook checks
> rs6000_long_double_type_size
> for long double (it's related to command line option -mlong-double-x)
> and
> some other targets like i386, also would like to check
> TARGET_LONG_DOUBLE_64
> and TARGET_LONG_DOUBLE_128.  But I think it isn't worse than before,
> without
> this change (with the previous macro), we used to define the macro
> with
> the things related to this command line options, which are still not
> ready.
> 
> #define LONG_DOUBLE_TYPE_SIZE rs6000_long_double_type_size
> 
> I debugged the code, jit::recording will see
> rs6000_long_double_type_size
> with the static initialized value zero, it means that the function 
> recording::memento_of_get_type::get_size would get zero byte size for
> the
> type (I assume that it's unexpected for the code?).  With this new
> hook,
> although it can provide not exact type size (can be off from the one
> specified by command line), it returns a reasonable size (comparing
> with
> the zero size).  From this perspective, it's slightly better?
> 
> +  if (ti == TI_LONG_DOUBLE_TYPE)
> +    return rs6000_long_double_type_size == FLOAT_PRECISION_TFmode ?
> TFmode
> +                                                                 :
> DFmode;

Thanks for looking into it.

Given the various points you make above, the patch is OK.

Thanks
Dave