#9577: String literals are wasting space -------------------------------------+------------------------------------- Reporter: xnyhps | Owner: xnyhps Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.8.2 (NCG) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Runtime | Related Tickets: performance bug | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:3 xnyhps]:
The main argument in favor of alignment seems to be: code often `memcpy`s string literals into buffers. By doing that with aligned addresses (apparently) SSE instructions can be used. This is irrelevant for GHC, because the strings are only parsed into `[Char]`s, never copied.
Will that always be the case if a string literal represents something like `Text` or `ByteString`? If so, will that continue to hold in the future? Might a future optimization fuse `putStr` with the conversion to do a copy? It may be that these concerns are baseless, but it might make sense to consider what alternative optimizations yours could preclude. You mention that there are a lot of string literals in the Prelude. I would bet that the vast majority of those are error messages. Might it be possible to specifically target ''exceptional'' strings that should never be anywhere speed-critical, and pack them all together? Putting them all together, ideally starting or ending on a page boundary, would (hopefully) mean that they wouldn't even need to be swapped in unless an error occurred. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9577#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler