On Wed, Oct 23, 2024 at 08:53:36PM +0200, Jakub Jelinek wrote:
> save_expr has been doing that at least since 1992, likely before that.
> Though, that
> 4073 /* Array ref is const/volatile if the array elements are
> 4074 or if the array is.. */
> 4075 TREE_READONLY (rval)
> 4076 |= (CP_TYPE_CONST_P (type) | TREE_READONLY (array));
> is done in the C++ FE also since 1994-ish.
>
> I'm afraid what will break especially in Ada if we change it.
> Though, unsure even to what.
>
> Are the TREE_READONLY flags needed on ARRAY_REFs/COMPONENT_REFs with
> ARRAY_REF bases etc.?
> If yes, are ARRAY_REFs/ARRAY_RANGE_REFs with non-invariant index (or
> possibly also non-invariant 3rd/4th argument or ARRAY_RANGE_REFs with
> non-invariant type size) the only problematic cases?
> Say TREE_READONLY COMPONENT_REF with VAR_DECL base should be invariant
> I'd hope.
> So, should we for the (TREE_READONLY (t) && !TREE_SIDE_EFFECTS (t))
> case walk the tree, looking for the ARRAY_REFs etc. and checking if that
> is really invariant?
Perhaps INDIRECT_REF/MEM_REF are similarly a problem, one could have
TREE_READONLY INDIRECT_REF or say COMPONENT_REF with INDIRECT_REF first
operand etc. and if the pointer which is dereferenced isn't invariant,
then the INDIRECT_REF/MEM_REF isn't invariant either.
Jakub
