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

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Dave,

May I ask if you still have some concerns on this patch with some
replies to your previous questions?

BR,
Kewen

on 2024/6/14 10:16, 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;
> 
> BR,
> Kewen
>