RFR: 8296389: C2: PhaseCFG::convert_NeverBranch_to_Goto must handle both orders of successors [v2]

[Emanuel Peter]

On Tue, 6 Dec 2022 11:33:12 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
>> 
>>  - Refactoring a bit after review suggestions
>>  - Merge branch 'master' into JDK-8296389
>>  - replace tabs with spaces
>>  - 8296389: C2: PhaseCFG::convert_NeverBranch_to_Goto must handle both orders of successors
>
> src/hotspot/share/opto/block.cpp line 626:
> 
>> 624:   int end_idx = b->end_idx();
>> 625:   int taken_idx = b->get_node(end_idx+1)->as_Proj()->_con;
>> 626:   ProjNode* alwaysTaken = b->get_node(end_idx + 1 + taken_idx)->as_Proj();
> 
> I find this code rather confusing. Since it's guaranteed that `alwaysTaken->_con == 0`, can't we simply do something like this?
> 
> ProjNode* alwaysTaken = b->get_node(end_idx)->as_MultiBranch()->proj_out(0);
> Block* succ ==  get_block_for_node(alwaysTaken->unique_ctrl_out_or_null());

👍

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PR: https://git.openjdk.org/jdk/pull/11481