#10400: Run time increases by 40% in fractal plotter core loop -------------------------------------+------------------------------------- Reporter: saffroy | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Runtime | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by rwbarton): Almost all the time is spent inside `iterations`, which is a 20-instruction long loop in both the 7.6 and 7.8 versions. The two loops are very similar, but some detail causes the 7.8 loop to run about 50% slower, probably some pipeline stall issue. It looks hard to even track down the exact issue, let alone deal with it in the code generator in a general way. I note that the LLVM backend produces a smaller loop which is a bit faster than even the 7.6 loop. The LLVM backend is usually good at optimizing this kind of non-allocating code. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10400#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler