Fix INLINE pragmas in desugarer

In #19969 we discovered that GHC has has a bug *forever* that means it
sometimes essentially discarded INLINE pragams.  This happened when you have
* Two more more mutually recursive functions
* Some of which (presumably not all!) have an INLINE pragma
* Completely monomorphic.

This hits a particular case in GHC.HsToCore.Binds.dsAbsBinds, which was
simply wrong -- it put the INLINE pragma on the wrong binder.

This patch fixes the bug, rather easily, by adjusting the
no-tyvar, no-dict case of GHC.HsToCore.Binds.dsAbsBinds.

I also discovered that the GHC.Core.Opt.Pipeline.shortOutIndirections
was not doing a good job for

    {-# INLINE lcl_id #-}
    lcl_id = BIG

    gbl_id = lcl_id

Here we want to transfer the stable unfolding to gbl_id (we do), but
we also want to remove it from lcl_id (we were not doing that).
Otherwise both Ids have large stable unfoldings.  Easily fixed.
Note [Transferring IdInfo] explains.

3 files changed, 54 insertions, 0 deletions

diff --git a/testsuite/tests/deSugar/should_compile/T19969.hs b/testsuite/tests/deSugar/should_compile/T19969.hs
new file mode 100644
index 0000000000..ad9546c84a
--- /dev/null
+++ b/testsuite/tests/deSugar/should_compile/T19969.hs
@@ -0,0 +1,15 @@
+{-# OPTIONS_GHC -dno-typeable-binds -O2 -fno-worker-wrapper #-}
+
+module T19969 where
+
+-- Three mutually recursive functions
+-- We want to inline g, h, keeping f as the loop breaker
+
+f x = reverse (g (x:: [Int])) :: [Int]
+
+{-# INLINE g #-}
+
+g x = reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (h x))))))))))))
+
+{-# INLINE h #-}
+h x = reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (reverse (f x))))))))))))
diff --git a/testsuite/tests/deSugar/should_compile/T19969.stderr b/testsuite/tests/deSugar/should_compile/T19969.stderr
new file mode 100644
index 0000000000..5e23785472
--- /dev/null
+++ b/testsuite/tests/deSugar/should_compile/T19969.stderr
@@ -0,0 +1,38 @@
+
+==================== Tidy Core ====================
+Result size of Tidy Core
+  = {terms: 12, types: 18, coercions: 0, joins: 0/0}
+
+Rec {
+-- RHS size: {terms: 3, types: 2, coercions: 0, joins: 0/0}
+f [Occ=LoopBreaker] :: [Int] -> [Int]
+[GblId, Arity=1, Str=<B>b, Cpr=b, Unf=OtherCon []]
+f = \ (x :: [Int]) -> f x
+end Rec }
+
+-- RHS size: {terms: 3, types: 2, coercions: 0, joins: 0/0}
+g [InlPrag=INLINE (sat-args=1)] :: [Int] -> [Int]
+[GblId,
+ Arity=1,
+ Str=<B>b,
+ Cpr=b,
+ Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True,
+         Guidance=ALWAYS_IF(arity=1,unsat_ok=False,boring_ok=True)
+         Tmpl= \ (x [Occ=Once1] :: [Int]) -> f x}]
+g = \ (x :: [Int]) -> f x
+
+-- RHS size: {terms: 3, types: 2, coercions: 0, joins: 0/0}
+h [InlPrag=INLINE (sat-args=1)] :: [Int] -> [Int]
+[GblId,
+ Arity=1,
+ Str=<B>b,
+ Cpr=b,
+ Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True,
+         WorkFree=True, Expandable=True,
+         Guidance=ALWAYS_IF(arity=1,unsat_ok=False,boring_ok=True)
+         Tmpl= \ (x [Occ=Once1] :: [Int]) -> f x}]
+h = \ (x :: [Int]) -> f x
+
+
+
diff --git a/testsuite/tests/deSugar/should_compile/all.T b/testsuite/tests/deSugar/should_compile/all.T
index 888369b849..6e6f486b4a 100644
--- a/testsuite/tests/deSugar/should_compile/all.T
+++ b/testsuite/tests/deSugar/should_compile/all.T
@@ -110,3 +110,4 @@ test('T14815', [], makefile_test, ['T14815'])
 test('T13208', [], makefile_test, ['T13208'])
 test('T16615', normal, compile, ['-ddump-ds -dsuppress-uniques'])
 test('T18112', [grep_errmsg('cast')], compile, ['-ddump-ds'])
+test('T19969', normal, compile, ['-ddump-simpl -dsuppress-uniques'])