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Re: [patch] fold-const.c (fold): Clean up use of variable "t".


On Fri, 19 Mar 2004, Kazu Hirata wrote:
> Now, some people may not like to declare a variable whose name is also
> used in an outer scope, but IMHO that would be a separate problem as
> addressing this problem would unnecessarily complicate the patch.
>
> 2004-03-19  Kazu Hirata  <kazu@cs.umass.edu>
>
> 	* fold-const.c (fold): Declare "t" locally if needed
> 	temporarily.  Remove "orig_t".


I really like this clean-up, but as Richard Kenner has suggested
the shadowing of "t" can be confusing, and without "shrink-wrapping"
can lead to larger stack frames for fold, which is often recursive.

Fortunately, most of the cases that you clean-up, require very short
life-times/scopes for the new local "t".  In these cases, I'd recommend
using the fold-scope "tem" variable.

e.g.

 	    if (REAL_VALUE_ISNAN (cst)
 		&& ! HONOR_SNANS (TYPE_MODE (TREE_TYPE (arg1))))
 	      {
-		t = (code == NE_EXPR) ? integer_one_node : integer_zero_node;
+		tem =
+		  (code == NE_EXPR) ? integer_one_node : integer_zero_node;
 		return omit_one_operand (type, fold_convert (type, tem),
					 arg0);
 	      }

i.e. use "tem" rather than "tree t".


However, I really like the concept of making "t" const, and completely
removing "orig_t".  For the remaining difficult cases you might consider
a recursive call to fold with the modified t, or alternatively you could
rename all uses of "t" between its modification and the next "return t".

Once this is done, I think we might be able to remove the fold_1 wrapper
used by --enable-checking=fold, as we should be able guarantee the input
tree is immutable (i.e. that fold is nondestructive).

Roger
--


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