bulat.ziganshin:
> Hello Andrew,
>
> Tuesday, May 20, 2008, 11:05:52 PM, you wrote:
>
> >> -funbox-strict-fields.
> >>
>
> > I did try that, but it didn't seem to make any difference for me. [Maybe
>
> it may be that ghc just not recompiled program when you supplied this
> switch. as i wrote, this switch by itself made your original program
> 1.5x faster on my box. try to delete .o/.exe before rebuilding
>
> and, without this switch representation for !Int32 is the same as for
> Int32 - only difference is that when data is assigned to such field
> they are evaluated first (and then boxed)
>
> it is not enabled by default, because for *non-primitive* datatypes
> such as B below automatic unboxing of strict fields of this type may
> decrease sharing and thus memory/performance. imagine for example:
>
> data A = A !B !B
> data B = B !Int !Int !Int !Int !Int
>
> b = B 1 1 1 1 1
> a = A b b
>
> jhc automatically unboxes strict fields of primitive datatypes, which
> is guaranteed to provide only positive effects. may be somesay the
> same will be added to ghc
I'm confused. GHC of course unboxes strict fields of primitive data types.
{-# OPTIONS -O2 -fvia-C -optc-O2 -funbox-strict-fields #-}
data A = A !B !B
data B = B !Int !Int !Int !Int !Int
b = B 1 2 3 4 5
a = A b b
go :: Int -> A
go 0 = a
go n = go (n-1)
main = print $ case go 10 of
A (B a b c d e) (B a' b' c' d' e') -> a + b + c + d + e
+ a' + b' + c' + d' + e'
For example, go compiles to:
$wgo :: Int#
-> (# Int#,
Int#,
Int#,
Int#,
Int#,
Int#,
Int#,
Int#,
Int#,
Int# #)
$wgo =
\ (ww_svf :: Int#) ->
case ww_svf of ds_Xmw {
__DEFAULT -> $wgo (-# ds_Xmw 1);
0 -> (# 1, 2, 3, 4, 5, 1, 2, 3, 4, 5 #)
Values are passed in registers, the structures are entirely unpacked into
registers or stack for return.
Were you not aware of this Bulat?
-- Don
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