RFR : 8218136: minor hotspot adjustments for xlclang++ from xlc16 on AIX

[Baesken, Matthias]

> 
> Confused. Which other xlc compilers set __GNUC_ as you are changing this
> for all of them? Though to be honest I don't understand this whole
> section anyway - we have a lengthy comment saying why you can't
> necessarily assign NULL to an integer type and to use NULL_WORD instead
> but then it's defined as NULL anyway! I wonder if we used to have some
> other conditions there where it was something different

Hi  David ,  not sure  but  I guess   the  #ifdef __GNUC__    came  from   linux/gcc and was copied to the  aix / xlc file  when the port was done back then .
See :

globalDefinitions_gcc.hpp

118#ifdef __GNUC__
119  #ifdef _LP64
120    #define NULL_WORD  0L
121  #else
122    // Cast 0 to intptr_t rather than int32_t since they are not the same type
123    // on platforms such as Mac OS X.
124    #define NULL_WORD  ((intptr_t)0)
125  #endif
126#else
127  #define NULL_WORD  NULL
128#endif

The NULL_WORD  is mostly used in x86-only coding.  But also used  at some (but few) places in shared coding , like :

intptr_t*   addr;
*addr = NULL_WORD;

intptr_t _callee_registers[RegisterMap::reg_count];
 _callee_registers[i] = src != NULL ? *src : NULL_WORD;


> In any case  having an if and else that do exactly the same thing seems rather
> pointless to me.
>

Yes I agree ,  I think I remove  the #ifdef  ... #else     and just define  #define NULL_WORD  NULL   for AIX .

Best regards, Matthias


> -----Original Message-----
> From: David Holmes <david.holmes at oracle.com>
> Sent: Freitag, 1. Februar 2019 05:24
> To: Baesken, Matthias <matthias.baesken at sap.com>; 'hotspot-
> dev at openjdk.java.net' <hotspot-dev at openjdk.java.net>
> Cc: 'build-dev at openjdk.java.net' <build-dev at openjdk.java.net>
> Subject: Re: RFR : 8218136: minor hotspot adjustments for xlclang++ from
> xlc16 on AIX
> 
> Hi Matthias,
> 
> On 1/02/2019 12:50 am, Baesken, Matthias wrote:
> > Please review  this small webrev  . It contains a few changes  for  building
> hotspot   on AIX with  xlclang++  / xlc16  .
> > ( most likely switching to   xlclang++  / xlc16    will be a must once  we
> introduce C++11/14 features )
> >
> > Some comments on the changes :
> >
> >
> > - porting_aix.cpp  :  workaround for demangle.h (does not work with
> xlclang++)
> 
> Can't comment as I know nothing about it.
> 
> > - arguments.cpp/hpp  :  the UNSUPPORTED_OPTON macro lead  to
> assigning false to  AllocateHeapAt which is a bad idea (and does not work
> with xlclang++)
> 
> Good catch!
> 
> > -   globalDefinitions_xlc.hpp   : xlclang++ sets   __GNUC__ so we must not
> have #error ... in this case
> 
> Confused. Which other xlc compilers set __GNUC_ as you are changing this
> for all of them? Though to be honest I don't understand this whole
> section anyway - we have a lengthy comment saying why you can't
> necessarily assign NULL to an integer type and to use NULL_WORD instead
> but then it's defined as NULL anyway! I wonder if we used to have some
> other conditions there where it was something different? In any case
> having an if and else that do exactly the same thing seems rather
> pointless to me.
> 
> Thanks,
> David
> >
> >
> >
> > Bug/webrev :
> >
> > https://bugs.openjdk.java.net/browse/JDK-8218136
> >
> > http://cr.openjdk.java.net/~mbaesken/webrevs/8218136.0/
> >
> >
> > Thanks, Matthias
> >