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.

Author: iabyn

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);			\

inline.h

@@ -2134,6 +2134,8 @@ Perl_cx_pushsub(pTHX_ PERL_CONTEXT *cx, CV *cv, OP *retop, bool hasargs)
     PERL_ARGS_ASSERT_CX_PUSHSUB;
 
     PERL_DTRACE_PROBE_ENTRY(cv);
+    cx->blk_sub.old_cxsubix     = PL_curstackinfo->si_cxsubix;
+    PL_curstackinfo->si_cxsubix = cx - PL_curstackinfo->si_cxstack;
     cx->blk_sub.cv = cv;
     cx->blk_sub.olddepth = CvDEPTH(cv);
     cx->blk_sub.prevcomppad = PL_comppad;
@@ -2160,6 +2162,7 @@ Perl_cx_popsub_common(pTHX_ PERL_CONTEXT *cx)
     CvDEPTH(cv) = cx->blk_sub.olddepth;
     cx->blk_sub.cv = NULL;
     SvREFCNT_dec(cv);
+    PL_curstackinfo->si_cxsubix = cx->blk_sub.old_cxsubix;
 }
 
 
@@ -2206,6 +2209,8 @@ Perl_cx_pushformat(pTHX_ PERL_CONTEXT *cx, CV *cv, OP *retop, GV *gv)
 {
     PERL_ARGS_ASSERT_CX_PUSHFORMAT;
 
+    cx->blk_format.old_cxsubix = PL_curstackinfo->si_cxsubix;
+    PL_curstackinfo->si_cxsubix= cx - PL_curstackinfo->si_cxstack;
     cx->blk_format.cv          = cv;
     cx->blk_format.retop       = retop;
     cx->blk_format.gv          = gv;
@@ -2239,6 +2244,7 @@ Perl_cx_popformat(pTHX_ PERL_CONTEXT *cx)
     cx->blk_format.cv = NULL;
     --CvDEPTH(cv);
     SvREFCNT_dec_NN(cv);
+    PL_curstackinfo->si_cxsubix = cx->blk_format.old_cxsubix;
 }
 
 
@@ -2247,6 +2253,8 @@ Perl_cx_pusheval(pTHX_ PERL_CONTEXT *cx, OP *retop, SV *namesv)
 {
     PERL_ARGS_ASSERT_CX_PUSHEVAL;
 
+    cx->blk_eval.old_cxsubix   = PL_curstackinfo->si_cxsubix;
+    PL_curstackinfo->si_cxsubix= cx - PL_curstackinfo->si_cxstack;
     cx->blk_eval.retop         = retop;
     cx->blk_eval.old_namesv    = namesv;
     cx->blk_eval.old_eval_root = PL_eval_root;
@@ -2282,6 +2290,7 @@ Perl_cx_popeval(pTHX_ PERL_CONTEXT *cx)
         cx->blk_eval.old_namesv = NULL;
         SvREFCNT_dec_NN(sv);
     }
+    PL_curstackinfo->si_cxsubix = cx->blk_eval.old_cxsubix;
 }
 
 

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)

scope.c

@@ -82,6 +82,7 @@ Perl_new_stackinfo(pTHX_ I32 stitems, I32 cxitems)
     si->si_next = 0;
     si->si_cxmax = cxitems - 1;
     si->si_cxix = -1;
+    si->si_cxsubix = -1;
     si->si_type = PERLSI_UNDEF;
     Newx(si->si_cxstack, cxitems, PERL_CONTEXT);
     /* Without any kind of initialising CX_PUSHSUBST()

sv.c

@@ -14690,6 +14690,7 @@ Perl_si_dup(pTHX_ PERL_SI *si, CLONE_PARAMS* param)
 
     nsi->si_stack	= av_dup_inc(si->si_stack, param);
     nsi->si_cxix	= si->si_cxix;
+    nsi->si_cxsubix	= si->si_cxsubix;
     nsi->si_cxmax	= si->si_cxmax;
     nsi->si_cxstack	= cx_dup(si->si_cxstack, si->si_cxix, si->si_cxmax, param);
     nsi->si_type	= si->si_type;