[commit: ghc] wip/T13861: WIP: cleverer tagging? (f23c042)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/T13861
Link       : http://ghc.haskell.org/trac/ghc/changeset/f23c0423f05d26e081b47f6382fe8f2a4610b022/ghc

>---------------------------------------------------------------

commit f23c0423f05d26e081b47f6382fe8f2a4610b022
Author: Gabor Greif <ggreif at gmail.com>
Date:   Tue Oct 17 00:21:06 2017 +0200

    WIP: cleverer tagging?


>---------------------------------------------------------------

f23c0423f05d26e081b47f6382fe8f2a4610b022
 compiler/codeGen/StgCmmClosure.hs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/compiler/codeGen/StgCmmClosure.hs b/compiler/codeGen/StgCmmClosure.hs
index 1da1f70..6daedba 100644
--- a/compiler/codeGen/StgCmmClosure.hs
+++ b/compiler/codeGen/StgCmmClosure.hs
@@ -354,7 +354,8 @@ type DynTag = Int       -- The tag on a *pointer*
 --    * big, otherwise.
 --
 -- Small families can have the constructor tag in the tag bits.
--- Big families only use the tag value 1 to represent evaluatedness.
+-- Big families only use the tag value 1..mAX_PTR_TAG to represent
+-- evaluatedness, the last one lumping together all overflowing ones.
 -- We don't have very many tag bits: for example, we have 2 bits on
 -- x86-32 and 3 bits on x86-64.
 
@@ -364,10 +365,12 @@ isSmallFamily dflags fam_size = fam_size <= mAX_PTR_TAG dflags
 tagForCon :: DynFlags -> DataCon -> DynTag
 tagForCon dflags con
   | isSmallFamily dflags fam_size = con_tag
-  | otherwise                     = 1
+  | con_tag < max_tag             = con_tag
+  | otherwise                     = max_tag
   where
     con_tag  = dataConTag con -- NB: 1-indexed
     fam_size = tyConFamilySize (dataConTyCon con)
+    max_tag = mAX_PTR_TAG dflags
 
 tagForArity :: DynFlags -> RepArity -> DynTag
 tagForArity dflags arity