During some experiments with GreenCard I stumbled across a serious
restriction in GHC. Here a short example (an small part of a program
generated by GreenCard):
--------------------------------------------------------------
module Foo where
bar :: Double -> Double -> Double -> IO ()
bar a0 a1 a2 = _casm_GC_ ``bar(%0,%1,%2);'' a0 a1 a2
--------------------------------------------------------------
panne@liesl: > ghc-3.01 -c -fglasgow-exts Foo.hs
panic! (the `impossible' happened):
Cannot allocate enough registers for primop (try rearranging code or
reducing number of arguments?) _casm_GC_ ``bar(%0,%1,%2);'' [(PrelST.State{-3L-}
PrelGHC.RealWorld{-3r-}) (PrelGHC.State#{-3K-} PrelGHC.RealWorld{-3r-})
PrelGHC.Double#{-39-} PrelGHC.Double#{-39-} PrelGHC.Double#{-39-}]
Please report it as a compiler bug to [EMAIL PROTECTED]
This can be tracked down to some (annoyingly small) constants in
fptools/ghc/includes/GhcConstants.lh:
...
%************************************************************************
%* *
\subsection[stg-reg-counts]{How many STG registers are there}
%* *
%************************************************************************
\begin{code}
#define MAX_VANILLA_REG 8
#define MAX_FLOAT_REG 4
#define MAX_DOUBLE_REG 2
\end{code}
...
The questions are: Why are these constants so small? Can GhcConstants.lh
simply be edited to give the STG machine more registers? I really wish
it would be that easy! Browsing through GHC's sources, I can't find a
place contradicting my hopes, but I bet something evil is lurking, anyway...
This restriction is really a show-stopper for me, so a quick fix would
be highly appreciated.
--
Sven Panne Tel.: +49/89/2178-2235
LMU, Institut fuer Informatik FAX : +49/89/2178-2211
LFE Programmier- und Modellierungssprachen Oettingenstr. 67
mailto:[EMAIL PROTECTED] D-80538 Muenchen
http://www.pms.informatik.uni-muenchen.de/mitarbeiter/panne
