optimize & rmv from public API Perl_tmps_grow and related code

Previously in PUSH_EXTEND_MORTAL__SV_C, "PL_tmps_ix + 1" would execute
twice, once for the nonmutable if(>=), then again after the potential
tmps_grow call. tmps_grow has an unused return register/void proto, put it
to use by returning ix.  Also change tmps_grow to take the result of
"PL_tmps_ix + the constant (usually 1) or non-constant (EXTEND_MORTAL)".
This avoid having to put the constant twice in machine code, once for the
if test, 2nd time for extend length param for tmps_grow call. For
non-constant/EXTEND_MORTAL usage, it allows the C optimizer to have the
length var to go out of liveness sooner if possible. Also the var used for
the if(>=) test is more likely to be in a register than length var.
So "if test variable" is closer on hand to the CPU than length var. In some
cases, if non-const len var isn't used again, it becomes the "ix" variable
by having PL_tmps_ix added to it. Change sv_2mortal to return sv instead
of NULL to remove a unique branch/block of machine code that assigns 0 to
return variable (Visual C didn't figure out return sv == returned NULL,
not sv). See also [perl #121845].

1 files changed, 1 insertions, 1 deletions

diff --git a/embed.fnc b/embed.fnc
index a06de68bfb..a0cac62e37 100644
--- a/embed.fnc
+++ b/embed.fnc
@@ -1787,7 +1787,7 @@ Apd	|void	|sv_utf8_encode |NN SV *const sv
 ApdM	|bool	|sv_utf8_decode |NN SV *const sv
 Apdmb	|void	|sv_force_normal|NN SV *sv
 Apd	|void	|sv_force_normal_flags|NN SV *const sv|const U32 flags
-Ap	|void	|tmps_grow	|SSize_t n
+pX	|SSize_t|tmps_grow_p	|SSize_t ix
 Apd	|SV*	|sv_rvweaken	|NN SV *const sv
 : This is indirectly referenced by globals.c. This is somewhat annoying.
 p	|int	|magic_killbackrefs|NN SV *sv|NN MAGIC *mg