[PATCH] PR46598 confusion

[Richard Guenther <rguenther at suse dot de>]

This clears up register pair constraint documentation by providing
an example.

Ok?

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 167076)
--- gcc/doc/md.texi	(working copy)
*************** The @code{di} register.
*** 2102,2108 ****
  
  @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.
--- 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
! for 32bit code 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 where you have to use the following variant:
! 
! @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.