gc problem with nested functions

[Jim Wilson]

Your Sept 3 change broke nested functions.

Fri Sep  3 18:16:01 1999  Bernd Schmidt  <bernds@cygnus.co.uk>

	Change obstack memory management and varasm constant pool handling so
 	that nested functions are treated like any other functions.
	...
	(immed_double_const): Don't walk const_double_chain outside a
	function, but don't treat nested functions specially anymore.

The particular problem I saw is segmentation faults from the ia64 port
while compiling execute/920612-2.c with optimization.  It died in
immed_double_const while searching const_double_chain, because there was
invalid RTL on that list.

The invalid RTL occurs because nested functions have current_obstack pointing
to the permanent_obstack.  Combine allocates undobuf on the current obstack,
and then frees it if a combination fails.  Since this is the permanent_obstack,
this also causes us to free the RTL that is allocated in immed_double_constant.

Nested functions have current_obstack pointing at permanent_obstack so that
we can easily save all RTL generated for the function until the end of the
module.  Normally, this would be the temporary_obstack, and it would be
freed when we are done with the function.

When the gc stuff is done, this shouldn't be a problem, but meanwhile I think
we still need special treatment for nested functions here.

Alternatively, for nested functions, we might try to switch current_obstack
from the permanent_obstack to the temporary_obstack after RTL generation ends
but before RTL optimization starts.  However, I suspect that it will be
tricky to get this right, and I didn't want to try it.

I haven't checked this in yet, in case you wanted to make a comment or
suggestion.  I expect to check this in Monday unless someone comes up with
a better solution.

Fri Sep 10 14:57:48 1999  Jim Wilson  <wilson@cygnus.com>

	* varasm.c (immed_double_const): Treat nested functions specially
	again.

Index: varasm.c
===================================================================
RCS file: /cvs/cvsfiles/devo/gcc/varasm.c,v
retrieving revision 1.240
diff -p -r1.240 varasm.c
*** varasm.c	1999/09/07 04:13:47	1.240
--- varasm.c	1999/09/10 21:57:11
*************** immed_double_const (i0, i1, mode)
*** 2087,2093 ****
    pop_obstacks ();
  
    /* Don't touch const_double_chain if not inside any function.  */
!   if (current_function_decl != 0)
      {
        CONST_DOUBLE_CHAIN (r) = const_double_chain;
        const_double_chain = r;
--- 2087,2100 ----
    pop_obstacks ();
  
    /* Don't touch const_double_chain if not inside any function.  */
!   /* ??? Also don't touch const_double_chain if we are inside a nested
!      function.  This is because nested functions have current_obstack pointing
!      to permanent_obstack instead of the normal temporary_obstack, thus the
!      above switch to the permanent obstack does not make the RTL safe.  This
!      is particularly a problem if called from combine.  Combine does an obfree
!      if a combination fails, thus freeing the RTL we just allocated above.
!      There may be other places that cause similar problems.  */
!   if (outer_function_chain == 0 && current_function_decl != 0)
      {
        CONST_DOUBLE_CHAIN (r) = const_double_chain;
        const_double_chain = r;