RFR: 8277850: C2: optimize mask checks in counted loops

[Vladimir Kozlov]

On Mon, 6 Dec 2021 08:42:09 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> src/hotspot/share/opto/mulnode.cpp line 1719:
>> 
>>> 1717: bool MulNode::AndIL_shift_and_mask(PhaseGVN* phase, Node* mask, Node* shift, BasicType bt) const {
>>> 1718:   if (mask == NULL || shift == NULL) {
>>> 1719:     return false;
>> 
>> You need to check `shift` for `TOP`.
>
> Code below:  
> 
> const TypeInteger* shift_t = phase->type(shift)->isa_integer(bt);
>   if (mask_t == NULL || shift_t == NULL) {
> 
> catches the case where shift is top, I think.

You are right. It is type check.

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PR: https://git.openjdk.java.net/jdk/pull/6697