sv.h: Turn off AMAGIC flag in Gv_AMG

This makes no functional changes.

If a stash has its AMAGIC flag on, then when the overload caches are
updated we can turn off the flag if it turns out that there is no
overloading.

Gv_AMG is the easiest place to unset this flag, as Gv_AMupdate has
‘return 0’ in more than one place.

This is for efficiency’s sake, as an object that inherits overloading
but then loses it through @ISA changes will still have to go through
extra checks due to SvAMAGIC returning true.

This also offsets an inefficiency to be introduced in later commits:
changes to @ISA will set the AMAGIC flag.

1 files changed, 2 insertions, 1 deletions

diff --git a/sv.h b/sv.h
index c3e6c5a9f5..8d09ccbd09 100644
--- a/sv.h
+++ b/sv.h
@@ -923,7 +923,8 @@ the scalar's value cannot change unless written to.
 
 #define SvGAMAGIC(sv)           (SvGMAGICAL(sv) || SvAMAGIC(sv))
 
-#define Gv_AMG(stash)           Gv_AMupdate(stash, FALSE)
+#define Gv_AMG(stash) \
+	(Gv_AMupdate(stash,FALSE) ? 1 : (HvAMAGIC_off(stash), 0))
 
 #define SvWEAKREF(sv)		((SvFLAGS(sv) & (SVf_ROK|SVprv_WEAKREF)) \
 				  == (SVf_ROK|SVprv_WEAKREF))