• Michal Terepeta's avatar
    Allow packing constructor fields · cca2d6b7
    Michal Terepeta authored
    This is another step for fixing #13825 and is based on D38 by Simon
    Marlow.
    
    The change allows storing multiple constructor fields within the same
    word. This currently applies only to `Float`s, e.g.,
    ```
    data Foo = Foo {-# UNPACK #-} !Float {-# UNPACK #-} !Float
    ```
    on 64-bit arch, will now store both fields within the same constructor
    word. For `WordX/IntX` we'll need to introduce new primop types.
    
    Main changes:
    
    - We now use sizes in bytes when we compute the offsets for
      constructor fields in `StgCmmLayout` and introduce padding if
      necessary (word-sized fields are still word-aligned)
    
    - `ByteCodeGen` had to be updated to correctly construct the data
      types. This required some new bytecode instructions to allow pushing
      things that are not full words onto the stack (and updating
      `Interpreter.c`). Note that we only use the packed stuff when
      constructing data types (i.e., for `PACK`), in all other cases the
      behavior should not change.
    
    - `RtClosureInspect` was changed to handle the new layout when
      extracting subterms. This seems to be used by things like `:print`.
      I've also added a test for this.
    
    - I deviated slightly from Simon's approach and use `PrimRep` instead
      of `ArgRep` for computing the size of fields.  This seemed more
      natural and in the future we'll probably want to introduce new
      primitive types (e.g., `Int8#`) and `PrimRep` seems like a better
      place to do that (where we already have `Int64Rep` for example).
      `ArgRep` on the other hand seems to be more focused on calling
      functions.
    Signed-off-by: Michal Terepeta's avatarMichal Terepeta <michal.terepeta@gmail.com>
    
    Test Plan: ./validate
    
    Reviewers: bgamari, simonmar, austin, hvr, goldfire, erikd
    
    Reviewed By: bgamari
    
    Subscribers: maoe, rwbarton, thomie
    
    GHC Trac Issues: #13825
    
    Differential Revision: https://phabricator.haskell.org/D3809
    cca2d6b7
ByteCodeGen.hs 72.1 KB