RFR: 8303970: C2 can not merge homogeneous adjacent two If

[Tobias Hartmann]

On Fri, 10 Mar 2023 14:37:06 GMT, Yi Yang <yyang at openjdk.org> wrote:

> Hi, can I have a review for this patch? It adds new Identity for BoolNode to lookup homogenous integer comparison, i.e. `Bool (CmpX a b)` is identity to `Bool (CmpX b a)`, in this way, we are able to merge the following two "identical" Ifs, which is not before.
> 
> 
>     public static void test(int a, int b) { // ok, identical ifs, apply split_if
>         if (a == b) {
>             int_field = 0x42;
>         } else {
>             int_field = 42;
>         }
>         if (a == b) {
>             int_field = 0x42;
>         } else {
>             int_field = 42;
>         }
>     }
> 
>     public static void test(int a, int b) { // do nothing
>         if (a == b) {
>             int_field = 0x42;
>         } else {
>             int_field = 42;
>         }
>         if (b == a) {
>             int_field = 0x42;
>         } else {
>             int_field = 42;
>         }
>     }

You probably need something similar to this:

https://github.com/openjdk/jdk/blob/5726d31e56530bbe7dee61ae04b126e20cb3611d/src/hotspot/share/opto/graphKit.cpp#L1323-L1327

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

PR: https://git.openjdk.org/jdk/pull/12978