On 7/4/07, Diego Novillo <[EMAIL PROTECTED]> 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 > gimplification. > >> 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 ARRAY_REF index. My proposal is that we add a predicate is_gimple_const() and is_gimple_invariant() such that is_gimple_invariant() is implemented as: bool is_gimple_invariant (tree expr) { if (is_gimple_const (expr)) return true; else 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 indexes.
... this is somewhat ugly to do for *PRE* (for FRE, it's not really) :)
