[PATCH] MachineCSE: Add a target query for the LookAheadLimit heurisitic

[Matthias Braun]

Hi Tom,

I don't know the history here, but as this does scan forward for each instruction of the basic block it looks like a way to avoid quadratic runtime behavior for (corner) cases with thousands of instructions in a basic block. I think it is no problem to go to a much higher limit than 5. But why go completely boundless, do you need a guarantee here that the CSE is happening?

- Matthias


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http://reviews.llvm.org/D9472

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