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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 <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
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