DmdAnal: Implement Boxity Analysis (#19871)

This patch fixes some abundant reboxing of `DynFlags` in
`GHC.HsToCore.Match.Literal.warnAboutOverflowedLit` (which was the topic
of #19407) by introducing a Boxity analysis to GHC, done as part of demand
analysis. This allows to accurately capture ad-hoc unboxing decisions previously
made in worker/wrapper in demand analysis now, where the boxity info can
propagate through demand signatures.

See the new `Note [Boxity analysis]`. The actual fix for #19407 is described in
`Note [No lazy, Unboxed demand in demand signature]`, but
`Note [Finalising boxity for demand signature]` is probably a better entry-point.

To support the fix for #19407, I had to change (what was)
`Note [Add demands for strict constructors]` a bit
(now `Note [Unboxing evaluated arguments]`). In particular, we now take care of
it in `finaliseBoxity` (which is only called from demand analaysis) instead of
`wantToUnboxArg`.

I also had to resurrect `Note [Product demands for function body]` and rename
it to `Note [Unboxed demand on function bodies returning small products]` to
avoid huge regressions in `join004` and `join007`, thereby fixing #4267 again.
See the updated Note for details.

A nice side-effect is that the worker/wrapper transformation no longer needs to
look at strictness info and other bits such as `InsideInlineableFun` flags
(needed for `Note [Do not unbox class dictionaries]`) at all. It simply collects
boxity info from argument demands and interprets them with a severely simplified
`wantToUnboxArg`. All the smartness is in `finaliseBoxity`, which could be moved
to DmdAnal completely, if it wasn't for the call to `dubiousDataConInstArgTys`
which would be awkward to export.

I spent some time figuring out the reason for why `T16197` failed prior to my
amendments to `Note [Unboxing evaluated arguments]`. After having it figured
out, I minimised it a bit and added `T16197b`, which simply compares computed
strictness signatures and thus should be far simpler to eyeball.

The 12% ghc/alloc regression in T11545 is because of the additional `Boxity`
field in `Poly` and `Prod` that results in more allocation during `lubSubDmd`
and `plusSubDmd`. I made sure in the ticky profiles that the number of calls
to those functions stayed the same. We can bear such an increase here, as we
recently improved it by -68% (in b760c1f).
T18698* regress slightly because there is more unboxing of dictionaries
happening and that causes Lint (mostly) to allocate more.

Fixes #19871, #19407, #4267, #16859, #18907 and #13331.

Metric Increase:
    T11545
    T18698a
    T18698b

Metric Decrease:
    T12425
    T16577
    T18223
    T18282
    T4267
    T9961

9 files changed, 12 insertions, 12 deletions

diff --git a/testsuite/tests/simplCore/should_compile/T13143.stderr b/testsuite/tests/simplCore/should_compile/T13143.stderr
index c4c2db7462..6123f91292 100644
--- a/testsuite/tests/simplCore/should_compile/T13143.stderr
+++ b/testsuite/tests/simplCore/should_compile/T13143.stderr
@@ -89,7 +89,7 @@ end Rec }
 g [InlPrag=[2]] :: Bool -> Bool -> Int -> Int
 [GblId,
  Arity=3,
- Str=<1L><1L><1P(L)>,
+ Str=<1L><1L><1!L>,
  Cpr=1,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
diff --git a/testsuite/tests/simplCore/should_compile/T13543.stderr b/testsuite/tests/simplCore/should_compile/T13543.stderr
index 90bda9792f..485f6fea41 100644
--- a/testsuite/tests/simplCore/should_compile/T13543.stderr
+++ b/testsuite/tests/simplCore/should_compile/T13543.stderr
@@ -1,8 +1,8 @@
 
 ==================== Strictness signatures ====================
 Foo.$trModule:
-Foo.f: <1P(1L)><1P(L)><1P(L)>
-Foo.g: <1P(1P(L),1P(L))>
+Foo.f: <1!P(1L)><1!L><1!L>
+Foo.g: <1!P(1!L,1!L)>
 
 
 
@@ -15,7 +15,7 @@ Foo.g: 1
 
 ==================== Strictness signatures ====================
 Foo.$trModule:
-Foo.f: <1P(1L)><1P(L)><1P(L)>
-Foo.g: <1P(1P(L),1P(L))>
+Foo.f: <1!P(1L)><1!L><1!L>
+Foo.g: <1!P(1!L,1!L)>
 
 
diff --git a/testsuite/tests/simplCore/should_compile/T18013.stderr b/testsuite/tests/simplCore/should_compile/T18013.stderr
index 5fe7eec578..134078e7e8 100644
--- a/testsuite/tests/simplCore/should_compile/T18013.stderr
+++ b/testsuite/tests/simplCore/should_compile/T18013.stderr
@@ -138,7 +138,7 @@ mapMaybeRule [InlPrag=[2]]
   :: forall a b. Rule IO a b -> Rule IO (Maybe a) (Maybe b)
 [GblId,
  Arity=1,
- Str=<1P(L,LCL(C1(C1(P(L,1P(L,L))))))>,
+ Str=<1!P(L,LCL(C1(C1(P(L,1L)))))>,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
          Guidance=ALWAYS_IF(arity=1,unsat_ok=True,boring_ok=False)
diff --git a/testsuite/tests/simplCore/should_compile/T3717.stderr b/testsuite/tests/simplCore/should_compile/T3717.stderr
index bd6417b729..f131214132 100644
--- a/testsuite/tests/simplCore/should_compile/T3717.stderr
+++ b/testsuite/tests/simplCore/should_compile/T3717.stderr
@@ -56,7 +56,7 @@ end Rec }
 foo [InlPrag=[2]] :: Int -> Int
 [GblId,
  Arity=1,
- Str=<1P(1L)>,
+ Str=<1!P(1L)>,
  Cpr=1,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
diff --git a/testsuite/tests/simplCore/should_compile/T3772.stdout b/testsuite/tests/simplCore/should_compile/T3772.stdout
index 96830336bc..c63beeca95 100644
--- a/testsuite/tests/simplCore/should_compile/T3772.stdout
+++ b/testsuite/tests/simplCore/should_compile/T3772.stdout
@@ -65,7 +65,7 @@ T3772.$wfoo
 foo [InlPrag=[final]] :: Int -> ()
 [GblId,
  Arity=1,
- Str=<1P(L)>,
+ Str=<1!L>,
  Cpr=1,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
diff --git a/testsuite/tests/simplCore/should_compile/T4201.stdout b/testsuite/tests/simplCore/should_compile/T4201.stdout
index 383d652757..1e338e43fd 100644
--- a/testsuite/tests/simplCore/should_compile/T4201.stdout
+++ b/testsuite/tests/simplCore/should_compile/T4201.stdout
@@ -1,4 +1,4 @@
   lift :: Foo -> T
   [HasNoCafRefs, LambdaFormInfo: LFReEntrant 1, Arity: 1,
-   Strictness: <1L>,
+   Strictness: <1!A>, CPR: 1,
    Unfolding: (bof `cast` (Sym (N:Foo[0]) %<'Many>_N ->_R <T>_R))]
diff --git a/testsuite/tests/simplCore/should_compile/T4908.stderr b/testsuite/tests/simplCore/should_compile/T4908.stderr
index c74c5ce2ff..9cfd79d1e0 100644
--- a/testsuite/tests/simplCore/should_compile/T4908.stderr
+++ b/testsuite/tests/simplCore/should_compile/T4908.stderr
@@ -59,7 +59,7 @@ end Rec }
 f [InlPrag=[2]] :: Int -> (Int, Int) -> Bool
 [GblId,
  Arity=2,
- Str=<1P(1L)><MP(A,MP(ML))>,
+ Str=<1!P(1L)><MP(A,MP(ML))>,
  Cpr=2,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
diff --git a/testsuite/tests/simplCore/should_compile/T4930.stderr b/testsuite/tests/simplCore/should_compile/T4930.stderr
index 9da0009f84..b8d14764ce 100644
--- a/testsuite/tests/simplCore/should_compile/T4930.stderr
+++ b/testsuite/tests/simplCore/should_compile/T4930.stderr
@@ -56,7 +56,7 @@ end Rec }
 foo [InlPrag=[2]] :: Int -> Int
 [GblId,
  Arity=1,
- Str=<1P(L)>,
+ Str=<1!L>,
  Cpr=1,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,
diff --git a/testsuite/tests/simplCore/should_compile/spec-inline.stderr b/testsuite/tests/simplCore/should_compile/spec-inline.stderr
index 2ba178e6bf..40746ff717 100644
--- a/testsuite/tests/simplCore/should_compile/spec-inline.stderr
+++ b/testsuite/tests/simplCore/should_compile/spec-inline.stderr
@@ -143,7 +143,7 @@ Roman.foo1 = GHC.Maybe.Just @Int Roman.foo2
 foo :: Int -> Int
 [GblId,
  Arity=1,
- Str=<1P(L)>,
+ Str=<1!L>,
  Cpr=1,
  Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
          WorkFree=True, Expandable=True,