Improve alias analysis of upvalues using a disambiguation hash value.

All upvalue objects hold a disambiguation hash value now.
It's built from the parent prototype and the slot number.
Different hash values imply the upvalues cannot alias.
Same hash values don't imply anything (collision or different closures).
Upvalue disambiguation makes use of a reduced hash due to IR contraints.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/lj_obj.h b/src/lj_obj.h
index 85d904f3..ecce03ed 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -397,7 +397,7 @@ typedef struct GCupval {
     };
   };
   MRef v;               /* Points to stack slot (open) or above (closed). */
-  int32_t unusedv;      /* For consistent alignment. */
+  uint32_t dhash;       /* Disambiguation hash: dh1 != dh2 => cannot alias. */
 } GCupval;
 
 #define uvprev(uv_)     (&gcref((uv_)->prev)->uv)