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, 0 deletions

diff --git a/cop.h b/cop.h
index 00396f04a4..f9bf85222d 100644
--- a/cop.h
+++ b/cop.h
@@ -585,6 +585,7 @@ C<*len>.  Upon return, C<*flags> will be set to either C<SVf_UTF8> or 0.
 /* subroutine context */
 struct block_sub {
     OP *	retop;	/* op to execute on exit from sub */
+    I32         old_cxsubix;  /* previous value of si_cxsubix */
     /* Above here is the same for sub, format and eval.  */
     PAD		*prevcomppad; /* the caller's PL_comppad */
     CV *	cv;
@@ -597,6 +598,7 @@ struct block_sub {
 /* format context */
 struct block_format {
     OP *	retop;	/* op to execute on exit from sub */
+    I32         old_cxsubix;  /* previous value of si_cxsubix */
     /* Above here is the same for sub, format and eval.  */
     PAD		*prevcomppad; /* the caller's PL_comppad */
     CV *	cv;
@@ -663,6 +665,7 @@ struct block_format {
 /* eval context */
 struct block_eval {
     OP *	retop;	/* op to execute on exit from eval */
+    I32         old_cxsubix;  /* previous value of si_cxsubix */
     /* Above here is the same for sub, format and eval.  */
     SV *	old_namesv;
     OP *	old_eval_root;
@@ -1026,6 +1029,7 @@ struct stackinfo {
     struct stackinfo *	si_next;
     I32			si_cxix;	/* current context index */
     I32			si_cxmax;	/* maximum allocated index */
+    I32			si_cxsubix;	/* topmost sub/eval/format */
     I32			si_type;	/* type of runlevel */
     I32			si_markoff;	/* offset where markstack begins for us.
 					 * currently used only with DEBUGGING,
@@ -1072,6 +1076,7 @@ typedef struct stackinfo PERL_SI;
 	}								\
 	next->si_type = type;						\
 	next->si_cxix = -1;						\
+	next->si_cxsubix = -1;						\
         PUSHSTACK_INIT_HWM(next);                                       \
 	AvFILLp(next->si_stack) = 0;					\
 	SWITCHSTACK(PL_curstack,next->si_stack);			\