[GHC] #14619: Output value of program changes upon compiling with -O optimizations

[GHC]

#14619: Output value of program changes upon compiling with -O optimizations
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        Reporter:  sheaf             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:  x86_64
 Type of failure:  Incorrect result  |  (amd64)
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by AndreasK):

 GHC-8.2 does mess up the register allocation/calling convention on the
 foreign call to sqrt.

 {{{
 call sqrt
    # born:    %r3 ... %r29 %r30 %r31 ...
    # w_dying: %r0 ... %r29 %r31 ...
 }}}

 The bad news is that there is a good chance that it only works on head
 because we use the sqrt assembly instruction instead which sidesteps the
 issue.

 {{{
 ...
     sqrtsd %vSSE_s3Lt,%vSSE_c3O1
     # born:    %vSSE_c3O1
 ...
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14619#comment:34>
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