1. Can you please give me an example of something bad that can happen to
the LHS. Maybe I'm missing something here.
In this case nothing, but if NEW were a subreg, it can change a lot.
3. Isn't it reasonable to expect that every instance on old_rtx will be
replaced by new_rtx even if it can't be simplified?
This is what I understand from the function's documentation.
But actually every expressions that can't be simplified is not replaced.
SET is not an expression, so it is not handled by simplify_replace_rtx.
I agree that it is confusing, that
x = simplify_replace_rtx (a, b, c);
is different from
x = simplify_rtx (replace_rtx (a, b, c));
So maybe all you need is changing the final "return x" to "return
replace_rtx (x, old, new);". I reckon this change would be much cleaner
than handling SET, but I would very much want to see what a GWP person
thinks about this.
Paolo
