[commit: packages/integer-gmp] master: Allocate initial 1-limb mpz_t on the Stack and introduce MPZ# type (7bdcadd)

[Edward Z. Yang]

Hey Herbert,

Is there a way to get rid of the stg_INTLIKE_closure hack?  I ask
because this hack will stop working if the HEAP_ALLOCED removal
patch hits mainline, because the way you need to access static closures
will change.

Cheers,
Edward

Excerpts from git's message of 2014-01-13 05:25:26 -0800:
> Repository : ssh://git@git.haskell.org/integer-gmp
> 
> On branch  : master
> Link       : http://ghc.haskell.org/trac/ghc/changeset/7bdcadda7e884edffb1427f0685493f3a2e5c5fa/integer-gmp
> 
> >---------------------------------------------------------------
> 
> commit 7bdcadda7e884edffb1427f0685493f3a2e5c5fa
> Author: Herbert Valerio Riedel <hvr at gnu.org>
> Date:   Thu Jan 9 00:19:31 2014 +0100
> 
>     Allocate initial 1-limb mpz_t on the Stack and introduce MPZ# type
>     
>     We now allocate a 1-limb mpz_t on the stack instead of doing a more
>     expensive heap-allocation (especially if the heap-allocated copy becomes
>     garbage right away); this addresses #8647.
>     
>     In order to delay heap allocations of 1-limb `ByteArray#`s instead of
>     the previous `(# Int#, ByteArray# #)` pair, a 3-tuple
>     `(# Int#, ByteArray#, Word# #)` is returned now. This tuple is given the
>     type-synonym `MPZ#`.
>     
>     This 3-tuple representation uses either the 1st and the 2nd element, or
>     the 1st and the 3rd element to represent the limb(s) (NB: undefined
>     `ByteArray#` elements must not be accessed as they don't point to a
>     proper `ByteArray#`, see also `DUMMY_BYTE_ARR`); more specifically, the
>     following encoding is used (where `⊥` means undefined/unused):
>     
>      -  (#  0#, ⊥, 0## #) -> value = 0
>      -  (#  1#, ⊥, w   #) -> value = w
>      -  (# -1#, ⊥, w   #) -> value = -w
>      -  (#  s#, d, 0## #) -> value = J# s d
>     
>     The `mpzToInteger` helper takes care of converting `MPZ#` into an
>     `Integer`, and allocating a 1-limb `ByteArray#` in case the
>     value (`w`/`-w`) doesn't fit the `S# Int#` representation).
>     
>     The following nofib benchmarks benefit from this optimization:
>     
>             Program      Size    Allocs   Runtime   Elapsed  TotalMem
>      ------------------------------------------------------------------
>          bernouilli     +0.2%     -5.2%      0.12      0.12     +0.0%
>              gamteb     +0.2%     -1.7%      0.03      0.03     +0.0%
>               kahan     +0.3%    -13.2%      0.17      0.17     +0.0%
>              mandel     +0.2%    -24.6%      0.04      0.04     +0.0%
>               power     +0.2%     -2.6%     -2.0%     -2.0%     -8.3%
>           primetest     +0.1%    -17.3%      0.06      0.06     +0.0%
>                 rsa     +0.2%    -18.5%      0.02      0.02     +0.0%
>                 scs     +0.1%     -2.9%     -0.1%     -0.1%     +0.0%
>              sphere     +0.3%     -0.8%      0.03      0.03     +0.0%
>              symalg     +0.2%     -3.1%      0.01      0.01     +0.0%
>      ------------------------------------------------------------------
>                 Min     +0.1%    -24.6%     -4.6%     -4.6%     -8.3%
>                 Max     +0.3%     +0.0%     +5.9%     +5.9%     +4.5%
>      Geometric Mean     +0.2%     -1.0%     +0.2%     +0.2%     -0.0%
>     
>     Signed-off-by: Herbert Valerio Riedel <hvr at gnu.org>
> 
> >---------------------------------------------------------------
> 
> 7bdcadda7e884edffb1427f0685493f3a2e5c5fa
>  GHC/Integer/GMP/Prim.hs |  105 +++++++++++++++-------
>  GHC/Integer/Type.lhs    |  164 ++++++++++++++++------------------
>  cbits/gmp-wrappers.cmm  |  224 +++++++++++++++++++++++++++++++++--------------
>  3 files changed, 306 insertions(+), 187 deletions(-)
> 
> Diff suppressed because of size. To see it, use:
> 
>     git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc 7bdcadda7e884edffb1427f0685493f3a2e5c5fa