#14372: CMM contains a bunch of tail-merging opportunities -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by AndreasK): I think this can be solved in two steps: ---- Change the Cmm generation for case statements: Currently we generate cmm of the sort {{{ ... case 1: goto foo; ... foo: Register = Value return(Register) }}} Instead we could inline this when generating the switch. {{{ #include "Cmm.h" test_entry() { switch [1 .. 8] R2 { case 1 : {R1 = 0; return();} ... case 8 : {R1 = 8; return();} } } }}} From what I've seen this hopefully won't change the generated assembly since GHC does this already when compiling the switch in the cases I looked at. ---- The second step would be to change the Assembly generated to something like the listing in [comment:17 the comment above]. I imagine a way to do that would be to: * Check if * Assignments are into the same register. * The rest of the code is the same * Collect all the constants, put them into a lookup table and generate assembly that uses the lookup table like [comment:17 above]. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14372#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler