[PATCH] Fix PR35607, another revenge of invariant addresses (ivopts)

[Eric Botcazou]

> IMHO there are two possible ways to solve these problems:
>
> 1) something like the patch below (up to details of
>    address_invariant_p, this is just a quick hack).

It's roughly equivalent to what I proposed here:
  http://gcc.gnu.org/ml/gcc/2007-07/msg00093.html
but I'm not convinced it's the correct approach because IIUC 
is_gimple_min_invariant does its job correctly.

> 2) making TREE_INVARIANT behave equivalently to this patch after
>    gimplification (or introducing a new tree flag with this altered
>    semantics)
>
> 2) seems complicated and possibly causing further problems, so I would
> propose to go with 1), unless there are compile-time performance
> problems due to this change.
>
> I tried to understand Diego's proposal
> (http://gcc.gnu.org/ml/gcc/2007-07/msg00097.html), however it seems to
> propose to keep relying on TREE_INVARIANT with its current semantics,
> which seems wrong -- I think middle-end should not use TREE_INVARIANT at
> all, as it is more or less redundant with SSA form,

I'd agree with this, TREE_INVARIANT should not be relied upon here, but why 
can't this problem be also solved by invoking the correct predicate in 
expand_simple_operations?  E.g. tree-ssa-ccp.c:ccp_decl_initial_min_invariant 
or tree-ssa-propagate.c:valid_gimple_expression_p?

-- 
Eric Botcazou