utf8_to_bytes_: Add ability to return a mortalized pv

This is a non-destructive conversion of the input into native bytes, and
with any new memory required set for destruction via SAVEFREEPV.  This
allows the caller to not have to be concerned at all if memory was
created or not.

A new macro is created that calls this internal function with the
correct parameter to force this behavior.

Author: khwilliamson

embed.fnc

@@ -3709,6 +3709,9 @@ Admp	|bool	|utf8_to_bytes_new_pv					\
 Admp	|bool	|utf8_to_bytes_overwrite				\
 				|NN U8 **s_ptr				\
 				|NN STRLEN *lenp
+Admp	|bool	|utf8_to_bytes_temp_pv					\
+				|NN U8 const **s_ptr			\
+				|NN STRLEN *lenp
 EMXp	|U8 *	|utf16_to_utf8	|NN U8 *p				\
 				|NN U8 *d				\
 				|Size_t bytelen 			\

embed.h

@@ -862,6 +862,7 @@
 # define utf8_to_bytes_(a,b,c,d)                Perl_utf8_to_bytes_(aTHX_ a,b,c,d)
 # define utf8_to_bytes_new_pv(a,b,c)            Perl_utf8_to_bytes_new_pv(aTHX,a,b,c)
 # define utf8_to_bytes_overwrite(a,b)           Perl_utf8_to_bytes_overwrite(aTHX,a,b)
+# define utf8_to_bytes_temp_pv(a,b)             Perl_utf8_to_bytes_temp_pv(aTHX,a,b)
 # define utf8_to_uvchr_buf_helper(a,b,c)        Perl_utf8_to_uvchr_buf_helper(aTHX_ a,b,c)
 # define utf8n_to_uvchr_msgs                    Perl_utf8n_to_uvchr_msgs
 # define uvchr_to_utf8(a,b)                     Perl_uvchr_to_utf8(aTHX,a,b)

proto.h

@@ -2382,7 +2382,6 @@ Perl_utf8_to_bytes_(pTHX_ U8 **s_ptr, STRLEN *lenp, U8 ** free_me,
                           Perl_utf8_to_bytes_arg result_as)
 {
     PERL_ARGS_ASSERT_UTF8_TO_BYTES_;
-    PERL_UNUSED_CONTEXT;
 
     if (result_as == PL_utf8_to_bytes_new_memory) {
         *free_me = NULL;
@@ -2574,7 +2573,13 @@ Perl_utf8_to_bytes_(pTHX_ U8 **s_ptr, STRLEN *lenp, U8 ** free_me,
     *lenp = d - d0;
 
     if (result_as != PL_utf8_to_bytes_overwrite) {
-        *s_ptr = *free_me = d0;
+        *s_ptr = d0;
+        if (result_as == PL_utf8_to_bytes_use_temporary) {
+            SAVEFREEPV(*s_ptr);
+        }
+        else {
+            *free_me = *s_ptr;
+        }
     }
 
     return true;

utf8.c

@@ -1321,6 +1321,9 @@ typedef enum {
 #define Perl_utf8_to_bytes_new_pv(mTHX, s, l, f)                            \
         Perl_utf8_to_bytes_(aTHX_ (U8 **) s, l, f,                          \
                                   PL_utf8_to_bytes_new_memory)
+#define Perl_utf8_to_bytes_temp_pv(mTHX, s, l)                              \
+        Perl_utf8_to_bytes_(aTHX_ (U8 **) s, l, INT2PTR(U8 **, 1),          \
+                                  PL_utf8_to_bytes_use_temporary)
 
 /* Do not use; should be deprecated.  Use isUTF8_CHAR() instead; this is
  * retained solely for backwards compatibility */