[project @ 2000-09-06 12:21:15 by simonmar]

When compiling code for a case where the scrutinee is a primitve
comparison operator, we used to place the tag in a variable whose
unique was always the same: `mkPseudoUnique1 1'.  This was mostly
harmless but confused the Stix inliner in the NCG into generating
slightly less efficient code when the variable was used twice in a
basic block.

This patch fixes the problem by generating a new unique by just
changing the "tag" of an existing unique, namely the case binder.

diff --git a/ghc/compiler/basicTypes/Unique.lhs b/ghc/compiler/basicTypes/Unique.lhs
index 5c76485..7d9c039 100644 (file)
--- a/ghc/compiler/basicTypes/Unique.lhs
+++ b/ghc/compiler/basicTypes/Unique.lhs
@@ -27,6 +27,7 @@ module Unique (
 
        incrUnique,                     -- Used for renumbering
        deriveUnique,                   -- Ditto
+       newTagUnique,                   -- Used in CgCase
        initTyVarUnique,
        initTidyUniques,
 
@@ -237,6 +238,7 @@ getKey              :: Unique -> Int#               -- for Var
 
 incrUnique     :: Unique -> Unique
 deriveUnique   :: Unique -> Int -> Unique
+newTagUnique   :: Unique -> Char -> Unique
 
 isTupleKey     :: Unique -> Bool
 \end{code}
@@ -254,6 +256,9 @@ incrUnique (MkUnique i) = MkUnique (i +# 1#)
 -- any of the uniques produced any other way
 deriveUnique (MkUnique i) delta = mkUnique 'X' (I# i + delta)
 
+-- newTagUnique changes the "domain" of a unique to a different char
+newTagUnique u c = mkUnique c i where (_,i) = unpkUnique u
+
 -- pop the Char in the top 8 bits of the Unique(Supply)
 
 -- No 64-bit bugs here, as long as we have at least 32 bits. --JSM

diff --git a/ghc/compiler/codeGen/CgCase.lhs b/ghc/compiler/codeGen/CgCase.lhs
index d2fb33a..481ef02 100644 (file)
--- a/ghc/compiler/codeGen/CgCase.lhs
+++ b/ghc/compiler/codeGen/CgCase.lhs
@@ -1,7 +1,7 @@
 %
 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %
-% $Id: CgCase.lhs,v 1.45 2000/08/02 14:13:27 rrt Exp $
+% $Id: CgCase.lhs,v 1.46 2000/09/06 12:21:15 simonmar Exp $
 %
 %********************************************************
 %*                                                     *
@@ -61,7 +61,7 @@ import TyCon          ( TyCon, isEnumerationTyCon, isUnboxedTupleTyCon,
                        )
 import Type            ( Type, typePrimRep, splitAlgTyConApp, 
                          splitTyConApp_maybe, repType )
-import Unique           ( Unique, Uniquable(..), mkPseudoUnique1 )
+import Unique           ( Unique, Uniquable(..), newTagUnique )
 import Maybes          ( maybeToBool )
 import Util
 import Outputable
@@ -143,9 +143,10 @@ alternatives (in which case we lookup the tag in the relevant closure
 table to get the closure).
 
 Being a bit short of uniques for temporary variables here, we use
-mkPseudoUnique1 to generate a temporary for the tag.  We can't use
-mkBuiltinUnique, because that occasionally clashes with some
-temporaries generated for _ccall_GC, amongst others (see CgExpr.lhs).
+newTagUnique to generate a new unique from the case binder.  The case
+binder's unique will presumably have the 'c' tag (generated by
+CoreToStg), so we just change its tag to 'C' (for 'case') to ensure it
+doesn't clash with anything else.
 
 \begin{code}
 cgCase (StgPrimApp op args res_ty)
@@ -155,7 +156,7 @@ cgCase (StgPrimApp op args res_ty)
 
     let tag_amode = case op of 
                        TagToEnumOp -> only arg_amodes
-                       _ -> CTemp (mkPseudoUnique1{-see above-} 1) IntRep
+                       _ -> CTemp (newTagUnique (getUnique bndr) 'C') IntRep
 
        closure = CVal (CIndex (CLbl (mkClosureTblLabel tycon) PtrRep) tag_amode PtrRep) PtrRep
     in