New GHC fails to specialize imported function
Hello all, I just installed the new Haskell platform for OS X. It seems to have caused a major performance regression for a program I'm working on, making it well over 25x slower. The culprit appears to be that the new GHC (7.10.2) fails to specialize an imported function. If I manually add a SPECIALIZE pragma, performance goes back to around what it used to be. The code in question is located at https://github.com/wyager/HNet . As it stands, the code takes about 30 seconds to run on my machine. With the previous haskell-platform, it only took about .9 seconds. If I modify Operations.hs and uncomment the SPECIALIZE pragma, runtime goes down to about 1.1 seconds (still slower for some reason, but not awful). To test, compile with -O2 (as the program makes heavy use of Data.Vector, which requires -fspec-constr for performance). Additionally, my experience doesn't seem to match https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_guide/pragmas.html#... in that if I add an INLINABLE pragma at the site of (••)'s definition and then try to SPECIALIZE it in a different file after importing, GHC tells me "Warning: SPECIALISE pragma on INLINE function probably won't fire: ‘••’". Cheers, Will
This sounds terrible. Please post a bug report at https://ghc.haskell.org/trac/ghc/wiki/ReportABug
Thanks!
Richard
On Jul 30, 2015, at 11:12 PM, William Yager
Hello all,
I just installed the new Haskell platform for OS X.
It seems to have caused a major performance regression for a program I'm working on, making it well over 25x slower.
The culprit appears to be that the new GHC (7.10.2) fails to specialize an imported function. If I manually add a SPECIALIZE pragma, performance goes back to around what it used to be.
The code in question is located at https://github.com/wyager/HNet .
As it stands, the code takes about 30 seconds to run on my machine. With the previous haskell-platform, it only took about .9 seconds.
If I modify Operations.hs and uncomment the SPECIALIZE pragma, runtime goes down to about 1.1 seconds (still slower for some reason, but not awful).
To test, compile with -O2 (as the program makes heavy use of Data.Vector, which requires -fspec-constr for performance).
Additionally, my experience doesn't seem to match https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_guide/pragmas.html#... in that if I add an INLINABLE pragma at the site of (••)'s definition and then try to SPECIALIZE it in a different file after importing, GHC tells me "Warning: SPECIALISE pragma on INLINE function probably won't fire: ‘••’".
Cheers, Will _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
participants (2)
-
Richard Eisenberg -
William Yager