[M3devel] [M3commit] CVS Update: cm3

[Mika Nystrom]

This reminds me, there used to be a bug in PM3... has it been fixed?  This code
was unreliable:

PROCEDURE P() =

  VAR a : T;

  PROCEDURE Q(b : U) =
    BEGIN a := saveSomethingAbout(b) END Q;

  BEGIN CallVisitor(Q) END P;

(Note that the M3 report says that while inner procedures may not
be assigned to variables, they may be passed as procedure parameters.
The workaround for the compiler bug is to use something called
"object-oriented programming".)

"Rodney M. Bates" writes:
>Antony, I can' tell from your posts whether this is what you did or not, but:
>
>m3gdb really needs for there to be a static link allocated space and stored, for
>_every_ nested procedure, even if there is nothing in the compiled code that uses
>it.  m3gdb accesses/passes static links in several situations, e.g., a user-typed
>call on a nested procedure constant, user-typed assignment of a nested procedure
>value to a procedure variable, user-typed call on a procedure variable (whose
>value might be nested or top-level), and just access to a variable that is nonlocal
>to the current frame.
>
>All of this has been implemented for some time, although it is distressingly
>fragile.  I have a number of times gone back in and fixed some case I thought
>I had working earlier.  I recently started seeing "invalid static link" messages
>again from m3gdb, after a hiatus.
>
>The variable access function is particularly important to me, as I often use nested
>procedures, especially a recursive nested procedure inside a parent that holds variables
>that are local to the whole recursive (dynamic) nest but not fully global.  Especially when
>the recursion is umpteen levels deep, it is a real pain to have to figure out how
>many levels to go "up" in the dynamic chain just to get to the immediate static parent
>to print one of its variables. And if you want to type a expression that mixes a local
>and a nonlocal variable, the feature is almost essential.
>
>So, I propose static links be there always, with the possible exception of at very
>high optimization levels.
>
>
>
>Antony Hosking wrote:
>> CVSROOT:	/usr/cvs
>> Changes by:	hosking at birch.	08/01/07 20:20:48
>> 
>> Modified files:
>> 	cm3/m3-sys/m3cc/gcc/gcc/: tree-nested.c 
>> 	cm3/m3-sys/m3cc/gcc/gcc/m3cg/: parse.c 
>> 
>> Log message:
>> 	Fix bug in procedure value comparison as revealed by p035 of m3tests.
>> 	The problem was that convert_all_function_calls was marking nested function
>> 	decls as *not* needing a static chain (DECL_NO_STATIC_CHAIN) when their bodies
>> 	and other nested procedures within them did not refer to any of their
>> 	variables.  In Modula-3 we still need the static chain (ie, procedure
>> 	environment) for procedure values so that they can be compared (tested
>> 	for equality) properly.  See the M3 language specification for details of
>> 	procedure types, which define a procedure as a triple, including its
>> 	environment.  The fix makes use of DECL_NONLOCAL on function decls to mark
>> 	them as needing the static chain to be preserved whenever a STATIC_CHAIN_EXPR
>> 	is created for the decl.
>> 
>> 
>
>-- 
>-------------------------------------------------------------
>Rodney M. Bates, retired assistant professor
>Dept. of Computer Science, Wichita State University
>Wichita, KS 67260-0083
>316-978-3922
>rodney.bates at wichita.edu