add PL_curstackinfo->si_cxsubix field

This tracks the most recent sub/eval/format context pushed onto the
context stack. Then make dopopto_cursub use it.

The previous value is saved in the cxt struct, and is restored whenever
the context is popped.

This adds a tiny overhead for every sub call, but speeds up other
operations, such as determining the caller context when returning a
value from a sub - this has to be dpne for every sub call where the last
expression is context sensitive, so its often a win.

1 files changed, 5 insertions, 1 deletions

diff --git a/pp_ctl.c b/pp_ctl.c
index 5dee09dddf..ef1ff8dd40 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -37,7 +37,11 @@
 #define RUN_PP_CATCHABLY(thispp) \
     STMT_START { if (CATCH_GET) return docatch(thispp); } STMT_END
 
-#define dopopto_cursub()	dopoptosub_at(cxstack, cxstack_ix)
+#define dopopto_cursub() \
+    (PL_curstackinfo->si_cxsubix >= 0        \
+        ? PL_curstackinfo->si_cxsubix        \
+        : dopoptosub_at(cxstack, cxstack_ix))
+
 #define dopoptosub(plop)	dopoptosub_at(cxstack, (plop))
 
 PP(pp_wantarray)