Fix a nasty infelicity in the size computation of CoreUnfold

[ghc-hetmet.git] / compiler / coreSyn / CoreUnfold.lhs

diff --git a/compiler/coreSyn/CoreUnfold.lhs b/compiler/coreSyn/CoreUnfold.lhs
index f83521c..654cfa7 100644 (file)
--- a/compiler/coreSyn/CoreUnfold.lhs
+++ b/compiler/coreSyn/CoreUnfold.lhs
@@ -319,9 +319,13 @@ sizeExpr bOMB_OUT_SIZE top_args expr
           _                -> funSize top_args fun (length val_args)
 
     ------------ 
-    size_up_alt (_con, _bndrs, rhs) = size_up rhs
+    size_up_alt (_con, _bndrs, rhs) = size_up rhs `addSizeN` 1
        -- Don't charge for args, so that wrappers look cheap
        -- (See comments about wrappers with Case)
+       --
+       -- IMPORATANT: *do* charge 1 for the alternative, else we 
+       -- find that giant case nests are treated as practically free
+       -- A good example is Foreign.C.Error.errrnoToIOError
 
     ------------
        -- These addSize things have to be here because