[project @ 2001-08-22 10:00:51 by simonpj]

-------------------------
	Fix a demand-analyser bug
	-------------------------

This bug led to "entered absent arg" errors.
The fix is in DmdAnal.dmdTransform

	-- Important!  If we Keep the constructor application, then
	-- we need the demands the constructor places (usually lazy)
	-- If not, we don't need to.  For example:
	--	f p@(x,y) = (p,y)	-- S(AL)
	--	g a b     = f (a,b)
	-- It's vital that we don't calculate Absent for a!

diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs
index aa26c74..8fead0c 100644 (file)
--- a/ghc/compiler/stranal/DmdAnal.lhs
+++ b/ghc/compiler/stranal/DmdAnal.lhs
@@ -518,11 +518,23 @@ dmdTransform sigs var dmd
 ------         DATA CONSTRUCTOR
   | isDataConId var,           -- Data constructor
     Seq k Now ds <- res_dmd,   -- and the demand looks inside its fields
-    let StrictSig dmd_ty = idNewStrictness var -- It must have a strictness sig
-  = if dmdTypeDepth dmd_ty == length ds then   -- Saturated, so unleash the demand
+    let StrictSig dmd_ty = idNewStrictness var,        -- It must have a strictness sig
+    let DmdType _ con_ds con_res = dmd_ty
+  = if length con_ds == length ds then -- Saturated, so unleash the demand
        -- ds can be empty, when we are just seq'ing the thing
-       mkDmdType emptyDmdEnv ds (dmdTypeRes dmd_ty)
-               -- Need to extract whether it's a product, hence dmdTypeRes
+       let 
+          arg_ds = case k of
+                       Keep -> zipWith lub ds con_ds
+                       Drop -> ds
+               -- Important!  If we Keep the constructor application, then
+               -- we need the demands the constructor places (usually lazy)
+               -- If not, we don't need to.  For example:
+               --      f p@(x,y) = (p,y)       -- S(AL)
+               --      g a b     = f (a,b)
+               -- It's vital that we don't calculate Absent for a!
+       in
+       mkDmdType emptyDmdEnv arg_ds con_res
+               -- Must remember whether it's a product, hence con_res, not TopRes
     else
        topDmdType