RFR: 8254269: simplify Node::disconnect_inputs [v2]

[Vladimir Kozlov]

On Sun, 11 Oct 2020 08:08:18 GMT, Xin Liu <xliu at openjdk.org> wrote:

>> 8254269: simplify Node::disconnect_inputs
>
> Xin Liu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8254269: simplify Node::disconnect_inputs
>   
>   Optimize it for the precedence loop. because there's no null between
>   2 non-null precedences, disconnect_inputs can break at a null value.

Changes requested by kvn (Reviewer).

src/hotspot/share/opto/node.cpp line 910:

> 908:     set_req(i, nullptr);
> 909:   }
> 910:

As Claes suggested:
   for (uint i = 0; i < req(); ++i) {
     if (in(i) != nullptr) {
       set_req(i, nullptr);
     }
   }

src/hotspot/share/opto/node.cpp line 914:

> 912:   // Note: Safepoints may have precedence edges, even during parsing
> 913:   // Precedences have no embedded NULL
> 914:   for (; i < len() && in(i) != nullptr; ++i) {

I don't think it is correct.

src/hotspot/share/opto/node.cpp line 916:

> 914:   for (; i < len() && in(i) != nullptr; ++i) {
> 915:     set_prec(i, nullptr);
> 916:   }

Something like next:
   for (uint i = req(); i < len(); ++i) {
     if (in(i) != nullptr) {
       set_prec(i, nullptr);
     }
   }

-------------

PR: https://git.openjdk.java.net/jdk/pull/589