[cmucl-ticket] [cmucl] #63: {{{VM::READ-CYCLE-COUNTER}}} destroys live values in ebx and ecx

[cmucl]

#63: {{{VM::READ-CYCLE-COUNTER}}} destroys live values in ebx and ecx
--------------------+-------------------------------------------------------
 Reporter:  rtoy    |       Owner:  somebody
     Type:  defect  |      Status:  new     
 Priority:  major   |   Milestone:          
Component:  Core    |     Version:  2012-09 
 Keywords:          |  
--------------------+-------------------------------------------------------
 Consider the following code:
 {{{
 (eval-when (:compile-toplevel :execute)
 (defmacro with-cycle-counter (&body body)
   (let ((hi0 (gensym))
         (hi1 (gensym))
         (lo0 (gensym))
         (lo1 (gensym)))
     `(multiple-value-bind (,lo0 ,hi0)
          (vm::read-cycle-counter)
        (values (locally , at body)
                (multiple-value-bind (,lo1 ,hi1)
                    (vm::read-cycle-counter)
                  (+ (ash (- ,hi1 ,hi0) 32)
                     (- ,lo1 ,lo0)))))))
 )

 (defun bar (x)
   (declare (type (and fixnum unsigned-byte) x)
            (optimize speed (safety 0)))
   (with-cycle-counter
     (let ((sum 0d0))
       (declare (double-float sum))
       (dotimes (k x)
         (declare (type (and fixnum unsigned-byte) k))
         (incf sum k))
       sum)))
 }}}

 When compiled, you get funny results like
 {{{
 * (bar 1000000)
 0.0d0
 408
 }}}

 This happens because {{{READ-CYCLE-COUNTER}}} uses the {{{CPUID}}}
 instruction that writes values to the eax, ebx, ecx, and edx registers,
 but the VOP for {{{READ-CYCLE-COUNTER}}} doesn't know that ebx and ecx are
 written.  Thus the vop can cause any live values in the ebx and ecx
 registers to be destroyed, as happens in this example.

-- 
Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/63>
cmucl <http://common-lisp.net/project/cmucl>
Cmucl is a high-performance, free Common Lisp implementation.