Avoid detoast in texteq/textne/byteaeq/byteane for unequal-length strings.

We can get the length of a compressed or out-of-line datum without actually
detoasting it.  If the lengths of two strings are unequal, we can then
conclude they are unequal without detoasting.  That saves considerable work
in an admittedly less-common case, without costing anything much when the
optimization doesn't apply.

Noah Misch

src/backend/utils/adt/varlena.c

@@ -1451,22 +1451,34 @@ text_cmp(text *arg1, text *arg2)
 Datum
 texteq(PG_FUNCTION_ARGS)
 {
-	text	   *arg1 = PG_GETARG_TEXT_PP(0);
-	text	   *arg2 = PG_GETARG_TEXT_PP(1);
+	Datum		arg1 = PG_GETARG_DATUM(0);
+	Datum		arg2 = PG_GETARG_DATUM(1);
 	bool		result;
+	Size		len1,
+				len2;
 
 	/*
 	 * Since we only care about equality or not-equality, we can avoid all the
-	 * expense of strcoll() here, and just do bitwise comparison.
+	 * expense of strcoll() here, and just do bitwise comparison.  In fact,
+	 * we don't even have to do a bitwise comparison if we can show the
+	 * lengths of the strings are unequal; which might save us from having
+	 * to detoast one or both values.
 	 */
-	if (VARSIZE_ANY_EXHDR(arg1) != VARSIZE_ANY_EXHDR(arg2))
+	len1 = toast_raw_datum_size(arg1);
+	len2 = toast_raw_datum_size(arg2);
+	if (len1 != len2)
 		result = false;
 	else
-		result = (memcmp(VARDATA_ANY(arg1), VARDATA_ANY(arg2),
-						 VARSIZE_ANY_EXHDR(arg1)) == 0);
+	{
+		text	   *targ1 = DatumGetTextPP(arg1);
+		text	   *targ2 = DatumGetTextPP(arg2);
 
-	PG_FREE_IF_COPY(arg1, 0);
-	PG_FREE_IF_COPY(arg2, 1);
+		result = (memcmp(VARDATA_ANY(targ1), VARDATA_ANY(targ2),
+						 len1 - VARHDRSZ) == 0);
+
+		PG_FREE_IF_COPY(targ1, 0);
+		PG_FREE_IF_COPY(targ2, 1);
+	}
 
 	PG_RETURN_BOOL(result);
 }
@@ -1474,22 +1486,28 @@ texteq(PG_FUNCTION_ARGS)
 Datum
 textne(PG_FUNCTION_ARGS)
 {
-	text	   *arg1 = PG_GETARG_TEXT_PP(0);
-	text	   *arg2 = PG_GETARG_TEXT_PP(1);
+	Datum		arg1 = PG_GETARG_DATUM(0);
+	Datum		arg2 = PG_GETARG_DATUM(1);
 	bool		result;
+	Size		len1,
+				len2;
 
-	/*
-	 * Since we only care about equality or not-equality, we can avoid all the
-	 * expense of strcoll() here, and just do bitwise comparison.
-	 */
-	if (VARSIZE_ANY_EXHDR(arg1) != VARSIZE_ANY_EXHDR(arg2))
+	/* See comment in texteq() */
+	len1 = toast_raw_datum_size(arg1);
+	len2 = toast_raw_datum_size(arg2);
+	if (len1 != len2)
 		result = true;
 	else
-		result = (memcmp(VARDATA_ANY(arg1), VARDATA_ANY(arg2),
-						 VARSIZE_ANY_EXHDR(arg1)) != 0);
+	{
+		text	   *targ1 = DatumGetTextPP(arg1);
+		text	   *targ2 = DatumGetTextPP(arg2);
 
-	PG_FREE_IF_COPY(arg1, 0);
-	PG_FREE_IF_COPY(arg2, 1);
+		result = (memcmp(VARDATA_ANY(targ1), VARDATA_ANY(targ2),
+						 len1 - VARHDRSZ) != 0);
+
+		PG_FREE_IF_COPY(targ1, 0);
+		PG_FREE_IF_COPY(targ2, 1);
+	}
 
 	PG_RETURN_BOOL(result);
 }
@@ -2358,23 +2376,31 @@ SplitIdentifierString(char *rawstring, char separator,
 Datum
 byteaeq(PG_FUNCTION_ARGS)
 {
-	bytea	   *arg1 = PG_GETARG_BYTEA_PP(0);
-	bytea	   *arg2 = PG_GETARG_BYTEA_PP(1);
-	int			len1,
-				len2;
+	Datum		arg1 = PG_GETARG_DATUM(0);
+	Datum		arg2 = PG_GETARG_DATUM(1);
 	bool		result;
+	Size		len1,
+				len2;
 
-	len1 = VARSIZE_ANY_EXHDR(arg1);
-	len2 = VARSIZE_ANY_EXHDR(arg2);
-
-	/* fast path for different-length inputs */
+	/*
+	 * We can use a fast path for unequal lengths, which might save us from
+	 * having to detoast one or both values.
+	 */
+	len1 = toast_raw_datum_size(arg1);
+	len2 = toast_raw_datum_size(arg2);
 	if (len1 != len2)
 		result = false;
 	else
-		result = (memcmp(VARDATA_ANY(arg1), VARDATA_ANY(arg2), len1) == 0);
+	{
+		bytea	   *barg1 = DatumGetByteaPP(arg1);
+		bytea	   *barg2 = DatumGetByteaPP(arg2);
 
-	PG_FREE_IF_COPY(arg1, 0);
-	PG_FREE_IF_COPY(arg2, 1);
+		result = (memcmp(VARDATA_ANY(barg1), VARDATA_ANY(barg2),
+						 len1 - VARHDRSZ) == 0);
+
+		PG_FREE_IF_COPY(barg1, 0);
+		PG_FREE_IF_COPY(barg2, 1);
+	}
 
 	PG_RETURN_BOOL(result);
 }
@@ -2382,23 +2408,31 @@ byteaeq(PG_FUNCTION_ARGS)
 Datum
 byteane(PG_FUNCTION_ARGS)
 {
-	bytea	   *arg1 = PG_GETARG_BYTEA_PP(0);
-	bytea	   *arg2 = PG_GETARG_BYTEA_PP(1);
-	int			len1,
-				len2;
+	Datum		arg1 = PG_GETARG_DATUM(0);
+	Datum		arg2 = PG_GETARG_DATUM(1);
 	bool		result;
+	Size		len1,
+				len2;
 
-	len1 = VARSIZE_ANY_EXHDR(arg1);
-	len2 = VARSIZE_ANY_EXHDR(arg2);
-
-	/* fast path for different-length inputs */
+	/*
+	 * We can use a fast path for unequal lengths, which might save us from
+	 * having to detoast one or both values.
+	 */
+	len1 = toast_raw_datum_size(arg1);
+	len2 = toast_raw_datum_size(arg2);
 	if (len1 != len2)
 		result = true;
 	else
-		result = (memcmp(VARDATA_ANY(arg1), VARDATA_ANY(arg2), len1) != 0);
+	{
+		bytea	   *barg1 = DatumGetByteaPP(arg1);
+		bytea	   *barg2 = DatumGetByteaPP(arg2);
 
-	PG_FREE_IF_COPY(arg1, 0);
-	PG_FREE_IF_COPY(arg2, 1);
+		result = (memcmp(VARDATA_ANY(barg1), VARDATA_ANY(barg2),
+						 len1 - VARHDRSZ) != 0);
+
+		PG_FREE_IF_COPY(barg1, 0);
+		PG_FREE_IF_COPY(barg2, 1);
+	}
 
 	PG_RETURN_BOOL(result);
 }