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