#14895: STG CSE makes dead binders undead -------------------------------------+------------------------------------- Reporter: hsyl20 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Debugging | Unknown/Multiple information is incorrect | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by osa1): Actually `isDeadBinder` check (the check that causes not printing case binders) is also used in code generation: {{{#!haskell cgCase (StgOpApp (StgPrimOp op) args _) bndr (AlgAlt tycon) alts | isEnumerationTyCon tycon -- Note [case on bool] = do { tag_expr <- do_enum_primop op args -- If the binder is not dead, convert the tag to a constructor -- and assign it. ; unless (isDeadBinder bndr) $ do { dflags <- getDynFlags ; tmp_reg <- bindArgToReg (NonVoid bndr) ; emitAssign (CmmLocal tmp_reg) (tagToClosure dflags tycon tag_expr) } ; (mb_deflt, branches) <- cgAlgAltRhss (NoGcInAlts,AssignedDirectly) (NonVoid bndr) alts -- See Note [GC for conditionals] ; emitSwitch tag_expr branches mb_deflt 0 (tyConFamilySize tycon - 1) ; return AssignedDirectly } }}} But this probably doesn't break anything because the scrutinee binder becomes undead only when (1) scrutinee is a data con application (2) the application repeats in an alternative. The code I showed above is for generating code when scrutinee is a primop application so it's safe. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14895#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler