[GHC] #12620: Allow the user to prevent floating and CSE

[GHC]

#12620: Allow the user to prevent floating and CSE
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        Reporter:  nomeata           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9520, #8457      |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 Replying to [comment:7 simonpj]:
 > I think that "noupdate" would require some careful thought.  What if I
 say
 > {{{
 > f x = if ... then Yield blah x
 >              else ...
 > }}}
 > Then the "noupdate" second field of `Yield` is just the parameter to
 `f`.  Does the caller have to know not to build an updatable thunk.

 I guess we would instruct the demand analysis to believe that `Yield` has
 strictness signature `<L,U><L,1*U>` and thus this once-used information
 will be propagated, at least to the extent possible.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12620#comment:10>
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