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From: jbs@WATSON.IBM.COM
Newsgroups: comp.arch
Subject: Re: IEEE arithmetic (Goldberg paper)
Message-ID: <9106190124.AA27410@ucbvax.Berkeley.EDU>
Date: 19 Jun 91 01:12:20 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 35


         I said:
>I think that if a (legal) program behaves differently when compiled with
>and without optimization that then the compiler is broken.  Perhaps you
>disagree.
         Malcolm said:
      B = 5.0
      IF ( ( B .GT. 3.0 ) .OR. MYTEST(A) )
          PRINT some diagnotic messages
      LOGICAL FUNCTION MYTEST(X)
      REAL X
      MYTEST = some boolean work
      PRINT a few diagnostics on the screen
      RETURN
      END
         I modified this to:
      LOGICAL*4 MYTEST
      B = 5.0
      IF ( ( B .GT. 3.0 ) .OR. MYTEST(B) )THEN
       WRITE(6,*)' MAIN'
      ENDIF
      END
      LOGICAL FUNCTION MYTEST(X)
      REAL X
      WRITE(6,*)' MYTEST'
      MYTEST = .TRUE.
      RETURN
      END
         I checked the behavior with the IBM VS Fortran and Xlf compi-
lers.  In both cases the behavior was not changed by optimization.  The
behavior differs between the two compilers but that is a different is-
sue.  So this example will not convince me that I'm wrong.  (Actually
I later softened my original statement to say it is undesirable for
optimization to affect a program's behavior.)
                       James B. Shearer