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

[Quan Anh Mai]

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;
>         }
>     }

May I ask why is global value numbering not able to merge these 2? Can we modify `BoolNode::hash` and `BoolNode::cmp` to take these into consideration?
Thanks a lot.

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