RFR: 8325144: C1: Optimize CriticalEdgeFinder

[Dean Long]

On Thu, 1 Feb 2024 16:49:02 GMT, Denghui Dong <ddong at openjdk.org> wrote:

> Hi,
> 
> Please help review this change that removed the sorting process in split_edges by checking if the 'to' block has been substituted.
> 
> Thanks

src/hotspot/share/c1/c1_Instruction.hpp line 2427:

> 2425:   BlockBegin* _from;
> 2426:   BlockBegin* _to;
> 2427:   int _index;

We don't really need `_to` anymore, because sux_at(_index) == _to if `insert_block_between` hasn't already processed this edge.  We can detect if sux_at(_index)  has been replaced in a couple different ways:
1. set a block flag on the newly inserted block
2. check the block_id on the newly inserted block, assume block ids increase monotonically.
But maybe the added complexity isn't worth it?  What's the performance improvement with this change vs the footprint increase for this new field?

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PR Review Comment: https://git.openjdk.org/jdk/pull/17674#discussion_r1487091733