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Re: About the is_gimple_min_invariant predicate
On 7/4/07, Diego Novillo <email@example.com> wrote:
On 7/4/07 6:24 PM, Eric Botcazou wrote:
>> The problem is that in GIMPLE we only allow TREE_INVARIANT as a gimple
>> value for ADDR_EXPRs. We still require a TREE_CONSTANT as an array
>> index. So, ARRAY[TREE_INVARIANT] is not valid GIMPLE.
> OK, my understanding is that is_gimple_min_invariant as currently written is
> correct as "non-recursive" predicate (for the updated grammar), i.e. during
>> FRE should refuse to substitute a TREE_INVARIANT expression as an
>> ARRAY_REF index.
> The problem is that FRE (and other optimization passes) uses it as an absolute
> predicate. This mostly works because it essentially encompasses terminals of
> the grammar, but fails for the non-terminal case.
> How would you fix that? By making it recursive, e.g.:
> or by uncoupling the 2 functions, i.e creating a recursive predicate for use
> outside of gimplification?
Passes ought to distinguish GIMPLE values from GIMPLE invariants
according to context. As this test case shows, a GIMPLE invariant is
not always the right value to replace as it cannot be used as a valid
My proposal is that we add a predicate is_gimple_const() and
is_gimple_invariant() such that is_gimple_invariant() is implemented as:
is_gimple_invariant (tree expr)
if (is_gimple_const (expr))
return TREE_INVARIANT (expr);
And is_gimple_const() is the current is_gimple_min_invariant() without
the ARRAY_REF case.
Okay, then i would think we should change things like FRE/PRE simply
use is_gimple_const, since ...
So my proposal is that PRE/FRE and the value propagators need to make
sure that they propagate is_gimple_invariant() except inside ARRAY_REF
... this is somewhat ugly to do for *PRE* (for FRE, it's not really) :)