[GHC] #10706: Make -fcpr-off a dynamic flag

[GHC]

#10706: Make -fcpr-off a dynamic flag
-------------------------------------+-------------------------------------
        Reporter:  darchon           |                   Owner:  darchon
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D1110
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Comment (by darchon):

 I have to confess that my use-case is very unconventional, perhaps even
 contrived:

 I work on a compiler that translates Haskell to circuits (www.clash-
 lang.org), and I use Streams to model sequential circuits:
 {{{
 data Stream a = a :- Stream a
 }}}
 Given this model of a sequential circuit, appending an element to a
 stream:
 {{{
 memory i s = i :- s
 }}}
 has a clear circuit semantics, it translates to a memory/latch.

 However, decomposing a stream:
 {{{
 case s of i :- s' -> ...
 }}}
 would basically translate to "looking into the future", which cannot be
 transformed into a circuit.

 I have taken great care that, under normal conditions, a case statement
 with a {{{Signal a}}} as a scrutinee never occurs. For one by not
 exporting the constructor of the {{{Steam}}} data type.

 However, due to the CPR analysis I sometimes end up with a worker/wrapper
 that looks something like this:
 {{{
 case memory i s of
   a :- bs -> g (#a,bs#)

 g (#a,bs#) = a :- bs
 }}}
 which gives me the troublesome case-decomposition on the {{{Stream}}} data
 type.

 Now, as to why I want {{{-fcpr-off}}} to be a dynamic flag: All my
 functions that manipulate the {{{Stream}}} type exist in a single module.
 If these functions get no CPR annotations, I noticed that the above
 troublesome worker/wrapper is never created elsewhere.
 The CPR annotations do not bother me in any of my other modules, and I do
 not want to turn off strictness analysis completely in the module where I
 define my {{{Stream}}}-manipulating functions. Hence I would like to have
 a {{{-fcpr-off}}} dynamic flag, so I can turn off CPR annotations just for
 that single module.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10706#comment:3>
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