[project @ 2001-05-04 08:09:42 by simonpj]

****	MERGE WITH 5.00 BRANCH     ********

	--------------------------------
	Make CPR work only for small products
	--------------------------------

GHC was barfing when doing CPR for programs involving very large
products.  A one-line fix in MkId.mkDataCon makes it only do CPR for
smaller products (I chose 10).  Comments

-- We do not treat very big tuples as CPR-ish:
--	a) for a start we get into trouble because there aren't
--	   "enough" unboxed tuple types (a tiresome restriction,
--	   but hard to fix),
--	b) more importantly, big unboxed tuples get returned mainly
--	   on the stack, and are often then allocated in the heap
--	   by the caller.  So doing CPR for them may in fact make
--	   things worse.

This should fix the error
	Failed to find interface decl for
		PrelGHC.(#,,,,,,,,,,,,,,,,,,,,,,,,
			  ,,,,,,,,,,,,,,,,,,,,,,,,,,,
			  ,,,,,,,,,,,,,,,,,,,,,,,#)

I hope.

diff --git a/ghc/compiler/basicTypes/MkId.lhs b/ghc/compiler/basicTypes/MkId.lhs
index e1ba24d..bee9eb4 100644 (file)
--- a/ghc/compiler/basicTypes/MkId.lhs
+++ b/ghc/compiler/basicTypes/MkId.lhs
@@ -31,6 +31,7 @@ module MkId (
 #include "HsVersions.h"
 
 
+import BasicTypes      ( Arity )
 import TysPrim         ( openAlphaTyVars, alphaTyVar, alphaTy, 
                          intPrimTy, realWorldStatePrimTy
                        )
@@ -151,10 +152,22 @@ mkDataConId work_name data_con
     tycon = dataConTyCon data_con
     cpr_info | isProductTyCon tycon && 
               isDataTyCon tycon    &&
-              arity > 0                = ReturnsCPR
+              arity > 0            &&
+              arity <= mAX_CPR_SIZE    = ReturnsCPR
             | otherwise                = NoCPRInfo
        -- ReturnsCPR is only true for products that are real data types;
        -- that is, not unboxed tuples or newtypes
+
+mAX_CPR_SIZE :: Arity
+mAX_CPR_SIZE = 10
+-- We do not treat very big tuples as CPR-ish:
+--     a) for a start we get into trouble because there aren't 
+--        "enough" unboxed tuple types (a tiresome restriction, 
+--        but hard to fix), 
+--     b) more importantly, big unboxed tuples get returned mainly
+--        on the stack, and are often then allocated in the heap
+--        by the caller.  So doing CPR for them may in fact make
+--        things worse.
 \end{code}
 
 The wrapper for a constructor is an ordinary top-level binding that evaluates