[MLton] possible x86 codegen bug with 64-bit ints

Stephen Weeks MLton@mlton.org
Fri, 21 Jan 2005 22:35:00 -0800

Scott Cruzen reported (a variant of) this bug on #sml.  MLton 20041109
generates incorrect code for the following program.

val args = CommandLine.arguments()
val _ =
      val stream = TextIO.getInstream (TextIO.openIn (hd args))
      val (str, stream) = TextIO.StreamIO.inputN (stream, 100)
      val pos = TextIO.StreamIO.filePosIn stream
      val _ = print (Position.toString pos)
      val _ = print "\n"
      val _ = TextIO.StreamIO.inputLine stream
      val _ = print (Position.toString pos)
      val _ = print "\n"

When run with a text file for its first argument, it should print


However, it instead prints


This is a very weird bug, since, as you can see in the code, "pos"
is an immutable value (a 64-bit integer).  The problem may be an x86
codegen bug, since the program works fine when compiled -codegen c or
-codegen bytecode.  Since the 64-bit stuff is pretty new, I suspect
that is the problem area.

Incidentally, when I tried to compile this program with the CVS head
MLton and -codegen bytecode, I got the following error:

missing opcode: Int32_storeStackOffset

I think this may have something to do with the recent changes (which I
haven't yet had time to investigate) to type synonym replacement in
the front end.