Prefer pg_any_to_server/pg_server_to_any over pg_do_encoding_conversion.

A large majority of the callers of pg_do_encoding_conversion were
specifying the database encoding as either source or target of the
conversion, meaning that we can use the less general functions
pg_any_to_server/pg_server_to_any instead.

The main advantage of using the latter functions is that they can make use
of a cached conversion-function lookup in the common case that the other
encoding is the current client_encoding.  It's notationally cleaner too in
most cases, not least because of the historical artifact that the latter
functions use "char *" rather than "unsigned char *" in their APIs.

Note that pg_any_to_server will apply an encoding verification step in
some cases where pg_do_encoding_conversion would have just done nothing.
This seems to me to be a good idea at most of these call sites, though
it partially negates the performance benefit.

Per discussion of bug #9210.

src/pl/plperl/plperl.c

@@ -3811,9 +3811,7 @@ hv_store_string(HV *hv, const char *key, SV *val)
 	char	   *hkey;
 	SV		  **ret;
 
-	hkey = (char *)
-		pg_do_encoding_conversion((unsigned char *) key, strlen(key),
-								  GetDatabaseEncoding(), PG_UTF8);
+	hkey = pg_server_to_any(key, strlen(key), PG_UTF8);
 
 	/*
 	 * This seems nowhere documented, but under Perl 5.8.0 and up, hv_store()
@@ -3841,9 +3839,7 @@ hv_fetch_string(HV *hv, const char *key)
 	char	   *hkey;
 	SV		  **ret;
 
-	hkey = (char *)
-		pg_do_encoding_conversion((unsigned char *) key, strlen(key),
-								  GetDatabaseEncoding(), PG_UTF8);
+	hkey = pg_server_to_any(key, strlen(key), PG_UTF8);
 
 	/* See notes in hv_store_string */
 	hlen = -(int) strlen(hkey);

src/pl/plperl/plperl_helpers.h

@@ -9,24 +9,11 @@
 static inline char *
 utf_u2e(char *utf8_str, size_t len)
 {
-	int			enc = GetDatabaseEncoding();
 	char	   *ret;
 
-	/*
-	 * When we are in a PG_UTF8 or SQL_ASCII database
-	 * pg_do_encoding_conversion() will not do any conversion (which is good)
-	 * or verification (not so much), so we need to run the verification step
-	 * separately.
-	 */
-	if (enc == PG_UTF8 || enc == PG_SQL_ASCII)
-	{
-		pg_verify_mbstr_len(enc, utf8_str, len, false);
-		ret = utf8_str;
-	}
-	else
-		ret = (char *) pg_do_encoding_conversion((unsigned char *) utf8_str,
-												 len, PG_UTF8, enc);
+	ret = pg_any_to_server(utf8_str, len, PG_UTF8);
 
+	/* ensure we have a copy even if no conversion happened */
 	if (ret == utf8_str)
 		ret = pstrdup(ret);
 
@@ -41,12 +28,14 @@ utf_u2e(char *utf8_str, size_t len)
 static inline char *
 utf_e2u(const char *str)
 {
-	char	   *ret =
-	(char *) pg_do_encoding_conversion((unsigned char *) str, strlen(str),
-									   GetDatabaseEncoding(), PG_UTF8);
+	char	   *ret;
 
+	ret = pg_server_to_any(str, strlen(str), PG_UTF8);
+
+	/* ensure we have a copy even if no conversion happened */
 	if (ret == str)
 		ret = pstrdup(ret);
+
 	return ret;
 }
 

src/pl/plpython/plpy_util.c

@@ -90,11 +90,9 @@ PLyUnicode_Bytes(PyObject *unicode)
 	{
 		PG_TRY();
 		{
-			encoded = (char *) pg_do_encoding_conversion(
-												(unsigned char *) utf8string,
-														 strlen(utf8string),
-														 PG_UTF8,
-													  GetDatabaseEncoding());
+			encoded = pg_any_to_server(utf8string,
+									   strlen(utf8string),
+									   PG_UTF8);
 		}
 		PG_CATCH();
 		{
@@ -109,7 +107,7 @@ PLyUnicode_Bytes(PyObject *unicode)
 	/* finally, build a bytes object in the server encoding */
 	rv = PyBytes_FromStringAndSize(encoded, strlen(encoded));
 
-	/* if pg_do_encoding_conversion allocated memory, free it now */
+	/* if pg_any_to_server allocated memory, free it now */
 	if (utf8string != encoded)
 		pfree(encoded);
 
@@ -149,10 +147,7 @@ PLyUnicode_FromString(const char *s)
 	char	   *utf8string;
 	PyObject   *o;
 
-	utf8string = (char *) pg_do_encoding_conversion((unsigned char *) s,
-													strlen(s),
-													GetDatabaseEncoding(),
-													PG_UTF8);
+	utf8string = pg_server_to_any(s, strlen(s), PG_UTF8);
 
 	o = PyUnicode_FromString(utf8string);
 

src/pl/tcl/pltcl.c

@@ -63,13 +63,17 @@
 static unsigned char *
 utf_u2e(unsigned char *src)
 {
-	return pg_do_encoding_conversion(src, strlen(src), PG_UTF8, GetDatabaseEncoding());
+	return (unsigned char *) pg_any_to_server((char *) src,
+											  strlen(src),
+											  PG_UTF8);
 }
 
 static unsigned char *
 utf_e2u(unsigned char *src)
 {
-	return pg_do_encoding_conversion(src, strlen(src), GetDatabaseEncoding(), PG_UTF8);
+	return (unsigned char *) pg_server_to_any((char *) src,
+											  strlen(src),
+											  PG_UTF8);
 }
 
 #define PLTCL_UTF