#15155: How untagged pointers sneak into banged fields -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: heisenbug Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.2 Resolution: | Keywords: CodeGen Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: 14677 Related Tickets: #13027 #7308 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): Just to write down what @simonpj and I discussed earlier today: it *would* be possible to ensure that a strict field of a constructor always points to a tagged value, by employing the same method we now use for `dataToTag#` (see Phab:D5201), namely have the code generator inject an eval for each strict field when building the constructor. The eval could be omitted in cases where the codegen can see that the value for the field is already a tagged value, these cases could include: * it's a constructor we just built * it's a case binder * the value was read from another strict constructor However, the extra eval would likely remain in many cases. But evals are cheap - just a tag test in the common case. Whether this ends up being a win or not is hard to say, it would be a good experiment to do though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15155#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler