#8472: Primitive string literals prevent optimization -------------------------------------+------------------------------------- Reporter: akio | Owner: xnyhps Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: newcomer Operating System: Linux | Architecture: x86_64 Type of failure: Runtime | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): While working on Phab:D1259 I came across another example of this issue (NB it requires my patch to trigger). The idea in that patch is to avoid inlining `String` literals and share them as top-level values instead. In order to keep using the REWRITE rules, we pretend that `unpackCString#` is CONLIKE. This has a side-effect of making GHC float the unboxed string literal out into a separate let-binder, which then prevents us from floating the `unpackCString#` application to the top-level, as unboxed literals aren't allowed there. Here's a simple example that triggers the behavior with the Phab:D1259 patch, but properly floats the `String`s on master. {{{ module Foo where draw xs = a ++ b ++ xs [a,b] = ["aa", "bb"] }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8472#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler