#3969: Poor performance of generated code on x86.
---------------------------------+------------------------------------------
Reporter: milan | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.12.1 | Keywords: x86, runtime performance
Os: Unknown/Multiple | Testcase:
Architecture: x86 | Failure: Runtime performance bug
---------------------------------+------------------------------------------
When implementing a hash function of !ByteStrings, I found the Haskell
implementation to be 2.5 slower than the equivalent C implementation.
The code of both functions is attached in [attachment:Hash.hs] and
[attachment:c_hash.c]. You can compile using
{{{
ghc -O --make Hash.hs c_hash.c
}}}
and run C implementation as {{{./Hash c bstr_len}}} and Haskell
implementation as {{{./Hash h bstr_len}}}.
There is no apparent problem in the Haskell implementation -- both the
```foldl'``` and the ```addWord8``` are inlined and everything in the main
loop is unboxed.
I believe the performance loss is because of bad register allocation. On
x86_64 is the Haskell implementation only ~1.2 times slower.
The comparison on Intel Xeon E5520 32-bit, Windows 7, GHC 6.12.1 is in
[attachment:res-32bit.txt]. C and Haskell implementation is run three
times, and on strings of length 10, 50 and 100. All times are in seconds.
The file also contains the assembler code of relevant methods.
On Intel Xeon E5320 64-bit, Fedora, GHC 6.12.1 is in [attachment:res-
64bit.txt].
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3969>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
