make the change to go_pap suggested in #4978. According to nofib, one

program is improved quite dramatically (fft2 30% less allocation), and
everything else was unchanged.

diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs
index a0a229f..4146b62 100644 (file)
--- a/compiler/coreSyn/CoreUtils.lhs
+++ b/compiler/coreSyn/CoreUtils.lhs
@@ -589,12 +589,10 @@ exprIsCheap' good_app other_expr  -- Applications and variables
     go _ _ = False
  
     --------------
-    go_pap args = all exprIsTrivial args
-       -- For constructor applications and primops, check that all
-       -- the args are trivial.  We don't want to treat as cheap, say,
-       --      (1:2:3:4:5:[])
-       -- We'll put up with one constructor application, but not dozens
-       
+    go_pap args = all (exprIsCheap' good_app) args
+        -- Used to be "all exprIsTrivial args" due to concerns about
+        -- duplicating nested constructor applications, but see #4978.
+
     --------------
     go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
        -- In principle we should worry about primops