Options to disable specific optimizations in TurboFan?

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TL

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Aug 25, 2022, 10:18:42 PM8/25/22
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I am curious whether there are any options for the 'd8' to disable specific TurboFan 
optimizations, e.g., simplified-lowering, type-lowering, etc, for all the optimization 
options or not. I know there are options for some optimizations, such as
escape-analysis, loop-peeling, etc. But, can we have control of "all" the optimizations
without actually modifying the v8 source code? 

Jakob Kummerow

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Aug 26, 2022, 4:58:37 AM8/26/22
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No, some Turbofan passes cannot be disabled, because they are required. SimplifiedLowering is a great example -- it changes ("lowers") the graph to the format that subsequent passes require.


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TL

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Aug 26, 2022, 10:22:50 AM8/26/22
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That makes sense.
Thank you for your answer.

Terrence Lim

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Aug 30, 2022, 9:37:06 AM8/30/22
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Hi Jakob,

I came across a follow-up question regarding the optimization phases.
What would happen (assume that we can) if we forcefully disable the mandatory phases, e.g., SimplifiedLowering?
Will the JIT compiler fail (crash) during the compilation?

Thanks! Regards

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HeuiChan (Terrence) Lim
PhD Student
Computer Science
The University of Arizona

Jakob Kummerow

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Aug 30, 2022, 10:05:19 AM8/30/22
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On Tue, Aug 30, 2022 at 3:37 PM Terrence Lim <heuich...@gmail.com> wrote:
Hi Jakob,

I came across a follow-up question regarding the optimization phases.
What would happen (assume that we can) if we forcefully disable the mandatory phases, e.g., SimplifiedLowering?
Will the JIT compiler fail (crash) during the compilation?

Yes.

Think of the different IR levels as different languages. They need to be translated ("lowered") into each other, and that chain must be complete. The translation steps in the middle are just as essential as translating from the input format to a high-level IR graph at the beginning, and translating from a low-level IR graph to machine code at the very end.

Terrence Lim

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Aug 30, 2022, 11:00:59 AM8/30/22
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That's what I roughly thought.
Thank you very much for your explanation.

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