Re: Work on gc-improv branch

[Paolo Bonzini <bonzini at gnu dot org>]

On 08/21/2009 10:52 AM, Laurynas Biveinis wrote:
> Trees and rtxes mostly. I haven't got around to taking a closer look,
> but for example folders love allocating temporary trees. For example,
> in tree-ssa-ccp.c:fold_gimple_assign,
>
> 	    if (COMPARISON_CLASS_P (op0))
> 	      {
> 		fold_defer_overflow_warnings ();
> 		tem = fold_binary_loc (cond_loc,
> 				   TREE_CODE (op0), TREE_TYPE (op0),
> 				   TREE_OPERAND (op0, 0),
> 				   TREE_OPERAND (op0, 1));
> 		/* This is actually a conditional expression, not a GIMPLE
> 		   conditional statement, however, the valid_gimple_rhs_p
> 		   test still applies.  */
> 		set = (tem&&  is_gimple_condexpr (tem)
> 		&&  valid_gimple_rhs_p (tem));
> 		fold_undefer_overflow_warnings (set, stmt, 0);
> 	      }
>
> Here tem should not be allocated on GC memory.

I disagree, as this would not apply to tem only but also to anything 
allocated to fold it.  This is not going to be maintainable (what if 
fold create temporary types, which need to be in GC memory definitely?).

Not having to deal with the lifetime of "temporary" stuff is part of 
having a GC, isn't it?

At most, you may want to add more ggc_free calls, but I don't think this 
is necessary either.  Actually, it would anyway miss any trees that are 
not toplevel and are created by the call to fold_binary_loc, so it would 
even be wrong in some sense.

Paolo