Re: [PATCH] PR46598 confusion

[Richard Guenther <rguenther at suse dot de>]

On Tue, 23 Nov 2010, Jan Hubicka wrote:

> > --- 2102,2130 ----
> >   
> >   @item A
> >   The @code{a} and @code{d} registers, as a pair (for instructions that
> > ! return half the result in one and half in the other).  For example
> 
> I would probably just remove 
> ", as a pair (for instructions that
> > ! return half the result in one and half in the other)"
> 
> and add something like "This class is used for instructions that return double
> word result in ax:dx pair. Single word values will be allocated either in ax or
> dx." To further prevent confusion that "A" imply register pair instead of class
> containing ax and bx.
> 
> The change is OK with me and I believe it belongs to x86 maintainership.

I have committed the following.

Thanks,
Richard.

2010-11-23  Richard Guenther  <rguenther@suse.de>

	* doc/md.texi (386 constraints): Clarify A constraint documentation.

Index: gcc/doc/md.texi
===================================================================
*** gcc/doc/md.texi	(revision 167079)
--- gcc/doc/md.texi	(working copy)
*************** The @code{si} register.
*** 2101,2108 ****
  The @code{di} register.
  
  @item A
! The @code{a} and @code{d} registers, as a pair (for instructions that
! return half the result in one and half in the other).
  
  @item f
  Any 80387 floating-point (stack) register.
--- 2101,2132 ----
  The @code{di} register.
  
  @item A
! The @code{a} and @code{d} registers.  This class is used for instructions
! that return double word results in the @code{ax:dx} register pair.  Single
! word values will be allocated either in @code{ax} or @code{dx}.
! For example on i386 the following implements @code{rdtsc}:
! 
! @smallexample
! unsigned long long rdtsc (void)
! @{
!   unsigned long long tick;
!   __asm__ __volatile__("rdtsc":"=A"(tick));
!   return tick;
! @}
! @end smallexample
! 
! This is not correct on x86_64 as it would allocate tick in either @code{ax}
! or @code{dx}.  You have to use the following variant instead:
! 
! @smallexample
! unsigned long long rdtsc (void)
! @{
!   unsigned int tickl, tickh;
!   __asm__ __volatile__("rdtsc":"=a"(tickl),"=d"(tickh));
!   return ((unsigned long long)tickh << 32)|tickl;
! @}
! @end smallexample
! 
  
  @item f
  Any 80387 floating-point (stack) register.