On Mon, 15 Dec 2025 02:36:06 GMT, Eric Fang <[email protected]> wrote:
>> src/hotspot/share/opto/vectornode.cpp line 1492:
>>
>>> 1490: // vector[n]{bool} => vector[n]{t} => vector[n]{bool}
>>> 1491: Node* in1 = VectorNode::uncast_mask(in(1));
>>> 1492: if (in1->Opcode() == Op_VectorLoadMask && length() ==
>>> in1->as_Vector()->length()) {
>>
>> Can there be a mismatch with the length? Can you give me an example?
>
> There are currently no such counterexamples. Because now we require the
> length of `VectorMaskCastNode` to be consistent with the length of its input
> node. But I'm not sure whether this restriction will be lifted in the future,
> and this optimization requires the length to be the same. Because of this
> requirement, I added this check. Similarly, in `uncast_mask` I also did the
> following assert:
> `assert(n->as_Vector()->length() == in1->as_Vector()->length(), "vector
> length must match");`
>
> Do you think it would be better to change this condition to an assert?
Yeah, currently we might not have such a real case that the length is not
matched, regardless whether there is mask casts inside the chain. At least I
cannot find such a case in API level. Not sure whether such pattern will be
generated by compiler itself in future due to some optimizations.
As an optimization of `VectorStoreMask (VectorLoadMask vect) => vec`, we must
make sure that the vector type before and after are exactly matched with each
other. Consider both the basic element type of `VectorStoreMask` and the input
of `VectorLoadMask` (i.e. the `vect`) are `boolean`, just checking the vector
length is enough.
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PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2617810466
