#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 heisenbug): `-fcmm-elim-common-blocks` helps a bit, but many equal ones are not caught: These hash the same {{{ hash_block c3dj 170 hash_block c3dp 170 hash_block c3dv 170 hash_block c3dB 170 }}} but are not commoned: {{{ ==================== Post switch plan ==================== {offset c3dj: // global R1 = R1 + 7; call (P64[(old + 8)])(R1) args: 8, res: 0, upd: 8; } ==================== Post switch plan ==================== {offset c3dp: // global R1 = R1 + 7; call (P64[(old + 8)])(R1) args: 8, res: 0, upd: 8; } ==================== Post switch plan ==================== {offset c3dv: // global R1 = R1 + 7; call (P64[(old + 8)])(R1) args: 8, res: 0, upd: 8; } ==================== Post switch plan ==================== {offset c3dB: // global R1 = R1 + 7; call (P64[(old + 8)])(R1) args: 8, res: 0, upd: 8; } }}} Maybe the reason is the "result register" updates are not considered in `CmmCommonBlockElim.hs`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14372#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler