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

4 files changed, 49 insertions, 0 deletions

diff --git a/testsuite/tests/ghci.debugger/scripts/T13825-debugger.hs b/testsuite/tests/ghci.debugger/scripts/T13825-debugger.hs
new file mode 100644
index 0000000000..0c3a1de219
--- /dev/null
+++ b/testsuite/tests/ghci.debugger/scripts/T13825-debugger.hs
@@ -0,0 +1,33 @@
+{-# LANGUAGE MagicHash #-}
+module T13825 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 #-} !Word16
+        {-# UNPACK #-} !Word64
+        {-# UNPACK #-} !Word32
+        {-# UNPACK #-} !Float
+        {-# UNPACK #-} !Double
+    deriving Show
+
+packed1 = Packed1 12.34# 56.78# 42# 99.99#
+packed2 = Packed2 12.34 56.78 42 99.99
+packed3 = Packed3 1 2 3 4 5 6 7.8 9.0
diff --git a/testsuite/tests/ghci.debugger/scripts/T13825-debugger.script b/testsuite/tests/ghci.debugger/scripts/T13825-debugger.script
new file mode 100644
index 0000000000..fc55ffc5dd
--- /dev/null
+++ b/testsuite/tests/ghci.debugger/scripts/T13825-debugger.script
@@ -0,0 +1,7 @@
+:l T13825-debugger.hs
+packed1
+:print packed1
+packed2
+:print packed2
+packed3
+:print packed3
diff --git a/testsuite/tests/ghci.debugger/scripts/T13825-debugger.stdout b/testsuite/tests/ghci.debugger/scripts/T13825-debugger.stdout
new file mode 100644
index 0000000000..6d3dc2f560
--- /dev/null
+++ b/testsuite/tests/ghci.debugger/scripts/T13825-debugger.stdout
@@ -0,0 +1,8 @@
+Packed1 12.34# 56.78# 42# 99.99#
+packed1 = Packed1 12.34 56.78 42 99.99
+Packed2 12.34 56.78 42 99.99
+packed2 = Packed2 12.34 56.78 42 99.99
+Packed3 1 2 3 4 5 6 7.8 9.0
+packed3 = Packed3
+            (GHC.Word.W8# 1) (GHC.Int.I8# 2) (GHC.Int.I64# 3) (GHC.Word.W16# 4)
+            (GHC.Word.W64# 5) (GHC.Word.W32# 6) 7.8 9.0
diff --git a/testsuite/tests/ghci.debugger/scripts/all.T b/testsuite/tests/ghci.debugger/scripts/all.T
index 00a39d704e..de3e7e37b2 100644
--- a/testsuite/tests/ghci.debugger/scripts/all.T
+++ b/testsuite/tests/ghci.debugger/scripts/all.T
@@ -95,3 +95,4 @@ test('getargs', extra_files(['../getargs.hs']), ghci_script, ['getargs.script'])
 test('T7386', normal, ghci_script, ['T7386.script'])
 test('T8557', normal, ghci_script, ['T8557.script'])
 test('T12458', normal, ghci_script, ['T12458.script'])
+test('T13825-debugger', normal, ghci_script, ['T13825-debugger.script'])