#9944: Performance issue -------------------------------------+------------------------------------- Reporter: clinton | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Runtime (amd64) | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- The runtime of the following code actually decreases if the number 2147483647 (2^31-1) is increased to 2147483648 (2^31). {{{#!hs f n = go 1 0 where go i c = if i == n then c + i else go (i+1) (c+i) main = print $ f (2147483647 :: Int) }}} I've attached two dumps from ghc-core, core7 is the 2147483647 case and core8 is the 2147483648 case, however the main differences are below: '''2147483647 case:''' {{{ _c3Qg: cmpq $2147483647,%r14 jne _c3Q9 _c3Qa: leaq 2147483647(%rsi),%rbx jmp *(%rbp) _c3Q9: addq %r14,%rsi incq %r14 jmp _c3Qg }}} '''2147483648 case:''' {{{ _c3Qg: movl $2147483648,%eax cmpq %rax,%r14 jne _c3Q9 _c3Qa: movl $2147483648,%eax movq %rsi,%rbx addq %rax,%rbx jmp *(%rbp) _c3Q9: addq %r14,%rsi incq %r14 jmp _c3Qg }}} Despite the extra instructions, the latter approach seems faster for my PC. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9944 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler