[cmucl-ticket] #20: Modular arith bug?

[cmucl]

#20: Modular arith bug?
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 Reporter:  rtoy    |       Owner:  somebody
     Type:  defect  |      Status:  new     
 Priority:  major   |   Milestone:          
Component:  Core    |     Version:  19e     
 Keywords:          |  
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 {{{
 (defun mat3neg (tt v)
   (ldb (byte 32 0) (ash v (- tt))))

 (defun mat3neg-a (tt v)
   (logand #xffffffff (ash v (- tt))))

 (defun zot (z2)
   (declare (type (unsigned-byte 32) z2)
            (optimize speed (safety 0)))
   (mat3neg -28 z2))

 (defun zot-a (z2)
   (declare (type (unsigned-byte 32) z2)
            (optimize speed (safety 0)))
   (mat3neg-a -28 z2))
 }}}

 Compile {{{zot}}} and there are lots of compiler notes, from
 {{{mat3neg}}}.  But compile {{{zot-a}}} and there's just one for boxing up
 the result.

 However, {{{zot}}} and {{{zot-a}}} are functionally identical, so
 {{{zot}}} and {{{zot-a}}} should produce the same code.  But {{{zot}}} has
 to do a full call to {{{ash}}} and {{{two-arg-and}}}.

 The {{{ldb}}} must be confusing the compiler somehow.

-- 
Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/20>
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