#8971: Native Code Generator for 7.8 is not as optimized as 7.6.3... --------------------------------------------+------------------------------ Reporter: GordonBGood | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler (NCG) | Version: 7.8.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime performance bug | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Changes (by simonmar): * milestone: => 7.10.1 Comment: I looked at this. The short version is that this isn't going to be easy to fix, and I recommend using LLVM. The new code generator generates better code for let-no-escapes than the old code generator. Whereas previously a let-no-escape would be a whole function with a fixed calling convention, with the new code generator it is just a label, and to call it we assign local variables for the arguments. All things being equal, this is a better way to do things, because we're not fixing the arguments to particular registers, and we're giving the later phases more flexibility to optimise. However, the register allocator in our NCG isn't very good, particularly with loops, and it ends up doing a worse job with the new code than the old, even though previously most of the arguments were actually passed on the Haskell stack. I don't think there are any easy tweaks to improve things, unfortunately. On 64-bit we get away with it because we have more registers. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8971#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler