Record evaluated-ness on workers and wrappers

Summary:
This patch is a refinement of the original commit (which
was reverted):

  commit 6b976eb89fe72827f226506d16d3721ba4e28bab
  Date:   Fri Jan 13 08:56:53 2017 +0000
      Record evaluated-ness on workers and wrappers

In Trac #13027, comment:20, I noticed that wrappers created after
demand analysis weren't recording the evaluated-ness of strict
constructor arguments.  In the ticket that led to a (debatable)
Lint error but in general the more we know about evaluated-ness
the better we can optimise.

This commit adds that info
  * both in the worker (on args)
  * and in the wrapper (on CPR result patterns).
See Note [Record evaluated-ness in worker/wrapper] in WwLib

On the way I defined Id.setCaseBndrEvald, and used it to shorten
the code in a few other places

Then I added test T13077a to test the CPR aspect of this patch,
but I found that Lint failed!

Reason: simpleOptExpr was discarding evaluated-ness info on
lambda binders because zapFragileIdInfo was discarding an
Unfolding of (OtherCon _).  But actually that's a robust
unfolding; there is no need to discard it. To fix this:

* zapFragileIdInfo only zaps fragile unfoldings

* Replace isClosedUnfolding with isFragileUnfolding (the latter
  is just the negation of the former, but the nomenclature is
  more consistent).  Better documentation too
       Note [Fragile unfoldings]

* And Simplify.simplLamBndr can now look at isFragileUnfolding
  to decide whether to use the longer route of simplUnfolding.

For some reason perf/compiler/T9233 improves in compile-time
allocation by 10%.  Hooray

Nofib: essentially no change:

--------------------------------------------------------------------------------
        Program           Size    Allocs   Runtime   Elapsed  TotalMem
--------------------------------------------------------------------------------
      cacheprof          +0.0%     -0.3%     +0.9%     +0.4%     +0.0%
--------------------------------------------------------------------------------
            Min          +0.0%     -0.3%     -2.4%     -2.4%     +0.0%
            Max          +0.0%     +0.0%     +9.8%    +11.4%     +2.4%
 Geometric Mean          +0.0%     -0.0%     +1.1%     +1.0%     +0.0%

3 files changed, 38 insertions, 1 deletions

diff --git a/testsuite/tests/stranal/should_compile/T13077.hs b/testsuite/tests/stranal/should_compile/T13077.hs
new file mode 100644
index 0000000000..193d39cb72
--- /dev/null
+++ b/testsuite/tests/stranal/should_compile/T13077.hs
@@ -0,0 +1,15 @@
+{-# LANGUAGE MagicHash #-}
+module T13077 where
+import GHC.Exts
+
+data X = A | B | C
+
+data T = MkT !X Int# Int#
+
+f (MkT x 0# _) = True
+f (MkT x n  _)  = let v = case x of
+                         A -> 1#
+                         B -> 2#
+                         C -> n
+                  in f (MkT x v v)
+ -- Tests evaluatedness for worker args
diff --git a/testsuite/tests/stranal/should_compile/T13077a.hs b/testsuite/tests/stranal/should_compile/T13077a.hs
new file mode 100644
index 0000000000..aeaee11875
--- /dev/null
+++ b/testsuite/tests/stranal/should_compile/T13077a.hs
@@ -0,0 +1,21 @@
+{-# LANGUAGE MagicHash  #-}
+module T13077a where
+
+import GHC.Exts
+
+data X = A | B | C
+
+data T = MkT !X Int# Int#
+
+g :: Int -> T
+g 0 = MkT A 1# 2#
+g n = g (n-1)
+
+boo :: Int -> T
+boo k = case g k of
+          MkT x n _ -> let v = case x of
+                                  A -> 1#
+                                  B -> 2#
+                                  C -> n
+                       in MkT x v v
+  -- Tests evaluated-ness for CPR
diff --git a/testsuite/tests/stranal/should_compile/all.T b/testsuite/tests/stranal/should_compile/all.T
index 5bbbfd5e55..d8fc7575cd 100644
--- a/testsuite/tests/stranal/should_compile/all.T
+++ b/testsuite/tests/stranal/should_compile/all.T
@@ -52,4 +52,5 @@ test('T11770', [ checkCoreString('OneShot') ], compile, ['-ddump-simpl'])
 test('T13031', normal, run_command,
          ['$MAKE -s --no-print-directory T13031'])
 
-
+test('T13077', normal, compile, [''])
+test('T13077a', normal, compile, [''])