sb-rotate-byte:rotate-byte broken on x86-64

[Robert Brown]

The function sb-rotate-byte:rotate-byte produces incorrect results
on x86-64 hosts when inlined.

Reproduce by doing the following:

Extract the attached file, bug.lisp.

Start SBCL on a 64-bit Intel host.

Evaluate
  (require 'sb-rotate-byte)
  (load "bug.lisp")
  (doit)

You should see the following output:

2987261130318898290 43 --> 5005609889943596700
8130673577157431119 30 --> 4358988824820830761
14432021153170023510 20 --> 17745709223287481625

Edit bug.lisp. Uncomment the SBCL-specific code in the
function rotate-right-64 and comment out the generic code.
Reload bug.lisp and evaluat
e (doit) again. You should see:

2987261130318898290 43 --> 16943545977209445855
8130673577157431119 30 --> 10648730343012924706
14432021153170023510 20 --> 7810677674261382285

The last number is different. It is the result of rotating right
by 21 bits instead of by 20.

bob

==========

sbcl --version
SBCL 1.0.52.31-05bb9b2-dirty

uname -a
Linux paradicsom.nyc.corp.google.com 2.6.38.8-gg621 #2 SMP Wed Sep 14 13:43:05 PDT 2011 x86_64 GNU/Linux

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 :SB-SOURCE-LOCATIONS :IEEE-FLOATING-POINT :X86-64 :UNIX :ELF :LINUX :SB-THREAD
 :LARGEFILE :GENCGC :STACK-GROWS-DOWNWARD-NOT-UPWARD :C-STACK-IS-CONTROL-STACK
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 :OS-PROVIDES-GETPROTOBY-R :OS-PROVIDES-POLL)

[Nikodemus Siivola (nikodemus)]

The bug occurs only if ROTATE-RIGHT-64 is inlined -- when the %64bit-rotate-byte/c version of the VOP is used.

Here's the fixed version -- commit coming tomorrowish.

(define-vop (%64bit-rotate-byte/c)
  (:policy :fast-safe)
  (:translate %unsigned-64-rotate-byte)
  (:note "inline 64-bit constant rotation")
  (:args (integer :scs (sb-vm::unsigned-reg) :target result))
  (:info count)
  (:arg-types (:constant (integer -63 63)) sb-vm::unsigned-num)
  (:results (result :scs (sb-vm::unsigned-reg)))
  (:result-types sb-vm::unsigned-num)
  (:generator 5
    (aver (not (= count 0)))
    (move result integer)
    (if (> count 0)
        (inst rol result count)
        (inst ror result (- count)))))

[Nikodemus Siivola (nikodemus)]

commit 6a71280af32d6bb02ed07d1a576df2cd9c5dfb79
Author: Nikodemus Siivola <email address hidden>
Date: Sat Oct 29 21:13:07 2011 +0300

    fix ROTATE-BYTE on 64-bit words using constant negative rotation

      Fixes lp#882151.