Changes between Version 15 and Version 16 of Status/Oct12


Ignore:
Timestamp:
Nov 1, 2012 10:47:46 AM (3 years ago)
Author:
simonmar
Comment:

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  • Status/Oct12

    v15 v16  
    3434 * dynlibs-by-default
    3535
    36  * new codegen by default
     36 * '''The new code generator.''' Several years since this project was started, the new code generator is finally working  [14], and is now switched on by default in `master`.  It will be in GHC 7.8.1.  From a user's perspective there should be very little difference, though some programs will be faster.
     37
     38 There are three important improvements in the generated code.  One is that `let-no-escape` functions are now compiled much more efficiently: a recursive `let-no-escape` now turns into a real loop in C--.  The second improvement is that global registers (R1, R2, etc.) are now available for the register allocator to use within a function, provided they aren't in use for argument passing.  This means that there are more registers available for complex code sequences.  The third improvement is that we have a new sinking pass that replaces the old "mini-inliner" from the native code generator, and is capable of optimisations that the old pass couldn't do.
     39
     40 Hand-written C-- code can now be written in a higher-level style with real function calls, and most of the hand-written C-- code in the RTS has been converted into the new style.  High-level C-- does not mention global registers such as R1 explicitly, nor does it manipulate the stack; all this is handled by the C-- code generator in GHC.  This is more robust and simpler, and means that we no longer need a special calling-convention for primops - they now use the same calling convention as ordinary Haskell functions.
     41
     42 We're interested in hearing about both performance improvements and regressions due to the new code generator.
    3743
    3844 * '''Improved floating point register allocation.''' On x86-64 there are now six machine registers available for any mixture of floating-point types. Previously a maximum of four values of type Float and two values of type Double could simultaneously be kept in machine registers.
     
    5561[12] Matching on type nats: [http://hackage.haskell.org/trac/ghc/wiki/TypeNats/MatchingOnNats] [[BR]]
    5662[13] Singletons and kinds: [http://hackage.haskell.org/trac/ghc/wiki/TypeNats/SingletonsAndKinds] [[BR]]
     63[14] The new codegen is nearly ready to go live [http://hackage.haskell.org/trac/ghc/blog/newcg-update] [[BR]]