Better sharing of join points (#19996)wip/T19557

This patch, provoked by regressions in the text package
(#19557), improves sharing of join points.  This also fixes
the terrible behaviour in #20049.

See Note [Duplicating join points] in GHC.Core.Opt.Simplify.

* In the StrictArg case of mkDupableContWithDmds, don't
  use Plan A for data constructors

* In postInlineUnconditionally, don't inline JoinIds
  Avoids inlining  join $j x = Just x
                   in case blah of
                         A -> $j x1
                         B -> $j x2
                         C -> $j x3

* In mkDupableStrictBind and mkDupableStrictAlt, create
  join points (much) more often: exprIsTrivial rather than
  exprIsDupable.  This may be much, but we'll see.

Metric Decrease:
    T12545
    T13253-spj
    T13719
    T18140
    T18282
    T18304
    T18698a
    T18698b
Metric Increase:
    T16577
    T18923
    T9961

2 files changed, 57 insertions, 0 deletions

diff --git a/testsuite/tests/perf/compiler/T20049.hs b/testsuite/tests/perf/compiler/T20049.hs
new file mode 100644
index 0000000000..2a6c1c56fc
--- /dev/null
+++ b/testsuite/tests/perf/compiler/T20049.hs
@@ -0,0 +1,53 @@
+{-# OPTIONS_GHC -O1 #-}
+module Repro where
+
+data A = A
+  { a1 :: (Maybe ())
+  , a2 :: (Maybe ())
+  , a3 :: (Maybe ())
+  , a4 :: (Maybe ())
+  , a5 :: (Maybe ())
+  , a6 :: (Maybe ())
+  , a7 :: (Maybe ())
+  , a8 :: (Maybe ())
+  , a9 :: (Maybe ())
+  , a10 :: (Maybe ())
+  , a11 :: (Maybe ())
+  , a12 :: (Maybe ())
+  }
+
+data B = B
+  { b1 :: !Bool
+  , b2 :: !Bool
+  , b3 :: !Bool
+  , b4 :: !Bool
+  , b5 :: !Bool
+  , b6 :: !Bool
+  , b7 :: !Bool
+  , b8 :: !Bool
+  , b9 :: !Bool
+  , b10 :: !Bool
+  , b11 :: !Bool
+  , b12 :: !Bool
+  }
+
+f :: Maybe () -> Bool
+f (Just ()) = True
+f Nothing = False
+
+g :: A -> B
+g (A a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12) =
+  B {
+      b1 = f a1
+    , b2 = f a2
+    , b3 = f a3
+    , b4 = f a4
+    , b5 = f a5
+    , b6 = f a6
+    , b7 = f a7
+    , b8 = f a8
+    , b9 = f a9
+    , b10 = f a10
+    , b11 = f a11
+    , b12 = f a12
+  }
diff --git a/testsuite/tests/perf/compiler/all.T b/testsuite/tests/perf/compiler/all.T
index ee764f15cb..6628fb377e 100644
--- a/testsuite/tests/perf/compiler/all.T
+++ b/testsuite/tests/perf/compiler/all.T
@@ -477,3 +477,7 @@ test('T11545',
 test('T15304',
      [ collect_compiler_stats('all', 10) ],
      compile, ['-O'])
+test ('T20049',
+      [ collect_compiler_stats('bytes allocated',2) ],
+      compile,
+      [''])