Allow packing constructor fields

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

3 files changed, 70 insertions, 0 deletions

diff --git a/testsuite/tests/primops/should_run/T13825-compile.hs b/testsuite/tests/primops/should_run/T13825-compile.hs
new file mode 100644
index 0000000000..04a72b38e9
--- /dev/null
+++ b/testsuite/tests/primops/should_run/T13825-compile.hs
@@ -0,0 +1,66 @@
+{-# LANGUAGE MagicHash #-}
+module Main where
+
+import GHC.Exts
+import Data.Word
+import Data.Int
+
+data Packed1 = Packed1 Float# Float# Int# Float#
+    deriving Show
+
+data Packed2 =
+    Packed2
+        {-# UNPACK #-} !Float
+        {-# UNPACK #-} !Float
+        {-# UNPACK #-} !Int
+        {-# UNPACK #-} !Float
+    deriving Show
+
+data Packed3 =
+    Packed3
+        {-# UNPACK #-} !Word8
+        {-# UNPACK #-} !Int8
+        {-# UNPACK #-} !Int64
+        {-# UNPACK #-} !Float
+        {-# UNPACK #-} !Word64
+        {-# UNPACK #-} !Word32
+        {-# UNPACK #-} !Float
+        {-# UNPACK #-} !Double
+    deriving Show
+
+packed1 = go 0.0# 1.0# 2# 3.0#
+  where
+    go a b c d =
+        Packed1 a b c d
+            : go (a `plusFloat#` 1.0#)
+                 (b `plusFloat#` 1.0#)
+               (c +# 1#)
+               (d `plusFloat#` 1.0#)
+
+packed2 =
+    [ Packed2
+        (fromIntegral i)
+        (fromIntegral (i + 1))
+        (fromIntegral (i + 2))
+        (fromIntegral (i + 3))
+    | i <- [0..]
+    ]
+
+packed3 =
+    [ Packed3
+        (fromIntegral i)
+        (fromIntegral (i + 1))
+        (fromIntegral (i + 2))
+        (fromIntegral (i + 3))
+        (fromIntegral (i + 4))
+        (fromIntegral (i + 5))
+        (fromIntegral (i + 6))
+        (fromIntegral (i + 6))
+    | i <- [0..]
+    ]
+
+main :: IO ()
+main = do
+    print (take 3 packed1)
+    print (take 3 packed2)
+    print (take 3 packed3)
diff --git a/testsuite/tests/primops/should_run/T13825-compile.stdout b/testsuite/tests/primops/should_run/T13825-compile.stdout
new file mode 100644
index 0000000000..41a5fb1368
--- /dev/null
+++ b/testsuite/tests/primops/should_run/T13825-compile.stdout
@@ -0,0 +1,3 @@
+[Packed1 0.0# 1.0# 2# 3.0#,Packed1 1.0# 2.0# 3# 4.0#,Packed1 2.0# 3.0# 4# 5.0#]
+[Packed2 0.0 1.0 2 3.0,Packed2 1.0 2.0 3 4.0,Packed2 2.0 3.0 4 5.0]
+[Packed3 0 1 2 3.0 4 5 6.0 6.0,Packed3 1 2 3 4.0 5 6 7.0 7.0,Packed3 2 3 4 5.0 6 7 8.0 8.0]
diff --git a/testsuite/tests/primops/should_run/all.T b/testsuite/tests/primops/should_run/all.T
index 68a2d5609f..30e871ac11 100644
--- a/testsuite/tests/primops/should_run/all.T
+++ b/testsuite/tests/primops/should_run/all.T
@@ -13,3 +13,4 @@ test('T10678',
      ],
      compile_and_run, ['-O'])
 test('T11296', normal, compile_and_run, [''])
+test('T13825-compile', normal, compile_and_run, [''])