Re: Fix usage of .GLOBAL_VAR

Re: Fix usage of .GLOBAL_VAR

[Richard Kenner]

    Kenner, unfortunately this fix does not seem related to the other Ada
    failure I mentioned earlier today.  Sorry.

I didn't think it was, but figured I might wait to be sure before
investing time into it.

Re: Fix usage of .GLOBAL_VAR

[Diego Novillo]

On Wed, 2004-07-28 at 14:30, Diego Novillo wrote:

> Bootstrapped and tested x86, x86-64 and ppc.
> 
I forgot to add: bootstrapped with --param global-var-threshold=0.


Diego.

Fix usage of .GLOBAL_VAR

[Diego Novillo]

When .GLOBAL_VAR is created the first time, we add it as an alias of all
the call-clobbered variables in the program.  However, the second time
we compute aliasing information, we not only don't create .GLOBAL_VAR
again, but we were clearing the may-alias sets of all the call-clobbered
variables and not restoring them.

This causes bootstrap problems with --param global-var-threshold=0 and
innumerable testsuite regressions due to bad code generation.

Kenner, unfortunately this fix does not seem related to the other Ada
failure I mentioned earlier today.  Sorry.

Bootstrapped and tested x86, x86-64 and ppc.


Diego.

	* tree-ssa-alias.c (maybe_create_global_var): Don't just
	return if .GLOBAL_VAR has been created.

Index: tree-ssa-alias.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-alias.c,v
retrieving revision 2.19
diff -d -c -p -r2.19 tree-ssa-alias.c
*** tree-ssa-alias.c	28 Jul 2004 05:13:08 -0000	2.19
--- tree-ssa-alias.c	28 Jul 2004 17:53:35 -0000
*************** maybe_create_global_var (struct alias_in
*** 1492,1524 ****
    size_t i, n_clobbered;
    
    /* No need to create it, if we have one already.  */
!   if (global_var)
!     return;
! 
!   /* Count all the call-clobbered variables.  */
!   n_clobbered = 0;
!   EXECUTE_IF_SET_IN_BITMAP (call_clobbered_vars, 0, i, n_clobbered++);
  
!   /* Create .GLOBAL_VAR if we have too many call-clobbered variables.
!      We also create .GLOBAL_VAR when there no call-clobbered variables
!      to prevent code motion transformations from re-arranging function
!      calls that may have side effects.  For instance,
  
!      		foo ()
  		{
  		  int a = f ();
  		  g ();
  		  h (a);
  		}
  
!      There are no call-clobbered variables in foo(), so it would be
!      entirely possible for a pass to want to move the call to f()
!      after the call to g().  If f() has side effects, that would be
!      wrong.  Creating .GLOBAL_VAR in this case will insert VDEFs for
!      it and prevent such transformations.  */
!   if (n_clobbered == 0
!       || ai->num_calls_found * n_clobbered >= (size_t) GLOBAL_VAR_THRESHOLD)
!     create_global_var ();
  
    /* If the function has calls to clobbering functions and .GLOBAL_VAR has
       been created, make it an alias for all call-clobbered variables.  */
--- 1492,1525 ----
    size_t i, n_clobbered;
    
    /* No need to create it, if we have one already.  */
!   if (global_var == NULL_TREE)
!     {
!       /* Count all the call-clobbered variables.  */
!       n_clobbered = 0;
!       EXECUTE_IF_SET_IN_BITMAP (call_clobbered_vars, 0, i, n_clobbered++);
  
!       /* Create .GLOBAL_VAR if we have too many call-clobbered
! 	 variables.  We also create .GLOBAL_VAR when there no
! 	 call-clobbered variables to prevent code motion
! 	 transformations from re-arranging function calls that may
! 	 have side effects.  For instance,
  
! 		foo ()
  		{
  		  int a = f ();
  		  g ();
  		  h (a);
  		}
  
! 	 There are no call-clobbered variables in foo(), so it would
! 	 be entirely possible for a pass to want to move the call to
! 	 f() after the call to g().  If f() has side effects, that
! 	 would be wrong.  Creating .GLOBAL_VAR in this case will
! 	 insert VDEFs for it and prevent such transformations.  */
!       if (n_clobbered == 0
! 	  || ai->num_calls_found * n_clobbered >= (size_t) GLOBAL_VAR_THRESHOLD)
! 	create_global_var ();
!     }
  
    /* If the function has calls to clobbering functions and .GLOBAL_VAR has
       been created, make it an alias for all call-clobbered variables.  */