Convert some casts to unconstify

These casts existed only to cast away a const qualifier.  Convert them
to unconstify to make that more explicit.

Reviewed-by: Rui Zhao <zhaorui126@gmail.com>
Discussion: https://www.postgresql.org/message-id/c76b72dd-5736-453a-b698-6968d42e4768%40eisentraut.org

src/backend/executor/execExpr.c

@@ -4312,7 +4312,7 @@ ExecBuildHash32Expr(TupleDesc desc, const TupleTableSlotOps *ops,
 	state->parent = parent;
 
 	/* Insert setup steps as needed. */
-	ExecCreateExprSetupSteps(state, (Node *) hash_exprs);
+	ExecCreateExprSetupSteps(state, unconstify(Node *, (const Node *) hash_exprs));
 
 	/*
 	 * Make a place to store intermediate hash values between subsequent

src/backend/replication/slot.c

@@ -420,7 +420,7 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 					errmsg("cannot enable failover for a temporary replication slot"));
 	}
 
-	INJECTION_POINT("replication-slot-create-begin", (char *) name);
+	INJECTION_POINT("replication-slot-create-begin", unconstify(char *, name));
 
 	/*
 	 * If some other backend ran this code concurrently with us, we'd likely

src/backend/storage/ipc/shmem.c

@@ -942,7 +942,7 @@ RegisterShmemCallbacks(const ShmemCallbacks *callbacks)
 	{
 		/* Remember the callbacks for later */
 		registered_shmem_callbacks = lappend(registered_shmem_callbacks,
-											 (void *) callbacks);
+											 unconstify(ShmemCallbacks *, callbacks));
 	}
 	else
 		elog(ERROR, "cannot request shared memory at this time");

src/backend/storage/smgr/md.c

@@ -1101,7 +1101,7 @@ mdwritev(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 		if (nblocks_this_segment != nblocks)
 			elog(ERROR, "write crosses segment boundary");
 
-		iovcnt = buffers_to_iovec(iov, (void **) buffers, nblocks_this_segment);
+		iovcnt = buffers_to_iovec(iov, unconstify(void **, buffers), nblocks_this_segment);
 		size_this_segment = nblocks_this_segment * BLCKSZ;
 		transferred_this_segment = 0;
 

src/backend/utils/mb/mbutils.c

@@ -1945,7 +1945,7 @@ pgwin32_message_to_UTF16(const char *str, int len, int *utf16len)
 		 */
 		if (IsTransactionState())
 		{
-			utf8 = (char *) pg_do_encoding_conversion((unsigned char *) str,
+			utf8 = (char *) pg_do_encoding_conversion((unsigned char *) unconstify(char *, str),
 													  len,
 													  msgenc,
 													  PG_UTF8);
@@ -1953,7 +1953,7 @@ pgwin32_message_to_UTF16(const char *str, int len, int *utf16len)
 				len = strlen(utf8);
 		}
 		else
-			utf8 = (char *) str;
+			utf8 = unconstify(char *, str);
 
 		utf16 = palloc_array(WCHAR, len + 1);
 		dstlen = MultiByteToWideChar(CP_UTF8, 0, utf8, len, utf16, len);

src/port/bsearch_arg.c

@@ -67,7 +67,7 @@ bsearch_arg(const void *key, const void *base0,
 		p = base + (lim >> 1) * size;
 		cmp = (*compar) (key, p, arg);
 		if (cmp == 0)
-			return (void *) p;
+			return unconstify(void *, p);
 		if (cmp > 0)
 		{						/* key > p: move right */
 			base = (const char *) p + size;

src/port/path.c

@@ -78,7 +78,7 @@ skip_drive(const char *path)
 	{
 		path += 2;
 	}
-	return (char *) path;
+	return unconstify(char *, path);
 }
 #else