Use wrappers of PG_DETOAST_DATUM_PACKED() more.

This makes almost all core code follow the policy introduced in the
previous commit.  Specific decisions:

- Text search support functions with char* and length arguments, such as
  prsstart and lexize, may receive unaligned strings.  I doubt
  maintainers of non-core text search code will notice.

- Use plain VARDATA() on values detoasted or synthesized earlier in the
  same function.  Use VARDATA_ANY() on varlenas sourced outside the
  function, even if they happen to always have four-byte headers.  As an
  exception, retain the universal practice of using VARDATA() on return
  values of SendFunctionCall().

- Retain PG_GETARG_BYTEA_P() in pageinspect.  (Page images are too large
  for a one-byte header, so this misses no optimization.)  Sites that do
  not call get_page_from_raw() typically need the four-byte alignment.

- For now, do not change btree_gist.  Its use of four-byte headers in
  memory is partly entangled with storage of 4-byte headers inside
  GBT_VARKEY, on disk.

- For now, do not change gtrgm_consistent() or gtrgm_distance().  They
  incorporate the varlena header into a cache, and there are multiple
  credible implementation strategies to consider.

1 files changed, 8 insertions, 10 deletions

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index a04fd7bc905..5f28a1a7c58 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -5342,13 +5342,12 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive, Oid collation,
 	}
 	else
 	{
-		bytea	   *bstr = DatumGetByteaP(patt_const->constvalue);
+		bytea	   *bstr = DatumGetByteaPP(patt_const->constvalue);
 
-		pattlen = VARSIZE(bstr) - VARHDRSZ;
+		pattlen = VARSIZE_ANY_EXHDR(bstr);
 		patt = (char *) palloc(pattlen);
-		memcpy(patt, VARDATA(bstr), pattlen);
-		if ((Pointer) bstr != DatumGetPointer(patt_const->constvalue))
-			pfree(bstr);
+		memcpy(patt, VARDATA_ANY(bstr), pattlen);
+		Assert((Pointer) bstr == DatumGetPointer(patt_const->constvalue));
 	}
 
 	match = palloc(pattlen + 1);
@@ -5858,13 +5857,12 @@ make_greater_string(const Const *str_const, FmgrInfo *ltproc, Oid collation)
 	}
 	else if (datatype == BYTEAOID)
 	{
-		bytea	   *bstr = DatumGetByteaP(str_const->constvalue);
+		bytea	   *bstr = DatumGetByteaPP(str_const->constvalue);
 
-		len = VARSIZE(bstr) - VARHDRSZ;
+		len = VARSIZE_ANY_EXHDR(bstr);
 		workstr = (char *) palloc(len);
-		memcpy(workstr, VARDATA(bstr), len);
-		if ((Pointer) bstr != DatumGetPointer(str_const->constvalue))
-			pfree(bstr);
+		memcpy(workstr, VARDATA_ANY(bstr), len);
+		Assert((Pointer) bstr == DatumGetPointer(str_const->constvalue));
 		cmpstr = str_const->constvalue;
 	}
 	else