[PATCH] D84228: [CodeGen][TargetPassConfig] Add unreachable-mbb-elimination pass explicitly

[Eugene Leviant via Phabricator via llvm-commits]

evgeny777 added a comment.

> Does this mean that we run UnreachableMachineBlockElimID twice?

If we execute pipeline normally (e.g llc -O3) then no. We'll pick previously added UnreachableMachineBlockElimID pass when scheduling LiveVariables pass (see PMTopLevelManager::schedulePass and findAnalysisPass)
The only way we can run UnreachableMachineBlockElimID twice is:

  llc -O3 -stop-after=unreachable-mbb-elimination foo.ll -o foo.mir
  llc -O3 -start-after=unreachable-mbb-elimination foo.mir -o foo.s

In the case above the second command will execute UnreachableMachineBlockElimID again (which is no-op due to absence of dead blocks)

> Is it safe to remove the addRequiredID case?

I don't think so. This can cause trouble with pipelines constructed using API calls.


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  https://reviews.llvm.org/D84228/new/

https://reviews.llvm.org/D84228