[PATCH 2/5][P1][tree-optimization/71437] Record more equivalences in some cases
Jeff Law
law@redhat.com
Thu Mar 16 15:03:00 GMT 2017
On 03/16/2017 06:54 AM, Trevor Saunders wrote:
>> + if (TREE_CODE (op0) == SSA_NAME && integer_zerop (op1))
>> + {
>> + enum tree_code code = eq->cond.ops.binary.op;
>> + if ((code == EQ_EXPR && eq->value == boolean_true_node)
>> + || (code == NE_EXPR && eq->value == boolean_false_node))
>> + derive_equivalencs_from_bit_ior (op0, const_and_copies);
>> +
>> + /* TODO: We could handle BIT_AND_EXPR in a similar fashion
>> + recording that the operands have a nonzero value. */
>> +
>> + /* TODO: We can handle more cases here, particularly when OP0 is
>> + known to have a boolean range. */
>
> I don't think its necessarily useful to put a list here of all possible
> improvements, but we could also handle things like if ((a | b) </> 0)
> since those imply !=.
The equivalences you derive here must hold for both objects. So without
additional range information you can't really determine anything about
(a | b) > 0.
If a and b are booleans or unsigned, then ideally we'd canonicalize the
test into an [in]equality test. At which point the existing code would
fire recording a = 0 and b = 0 on the false edge. You still can't
record anything on the true edge. I don't think we're good at the
canonicalization these days.
For (a & b) != 0, unconstrained we could record a != 0 and b != 0 on the
true edge, but nothing can be recorded on the false edge.
If we know a and b have boolean ranges we can refine that to a = 1 and b
= 1 on the true edge, but again, nothing can be recorded on the false edge.
Jeff
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