[GHC] #12982: Missed constant folding oportunities

[GHC]

#12982: Missed constant folding oportunities
-------------------------------------+-------------------------------------
        Reporter:  erikd             |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  libraries/hoopl   |              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:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

@@ -5,1 +5,1 @@
- {{#!hs
+ {{{#!hs

New description:

 A work colleague of mine found that some expressions were not being
 constant folded as expected.

 For example:
 {{{#!hs
 module Test where
 import Data.Int
 number :: Int64
 number = 2 ^ 10 - 3
 }}}
 compiled using:
 {{{
 ghc -O2 -keep-s-file -c test.hs
 }}}
 should result in an assembler file containing the constant `1021` but
 doesn't. However, if I change the above expression to:

 {{{
 number = 1024 -3
 }}}
 then the output assembler files does contain the value `1021`.

 I did a bit of a search and found some constant folding code in the
 `hoopl` library, but that doesn't seem to be what GHC actually uses.

--

Comment (by simonpj):

 I suspect it's just that the constant folding RULES, in `prelude/Build

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12982#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler