RFR: 8266746: C1: Replace UnsafeGetRaw with UnsafeGetObject when setting up OSR entry block [v3]

[Yi Yang]

On Wed, 26 May 2021 05:39:26 GMT, Dean Long <dlong at openjdk.org> wrote:

> It looks like when JDK-8150921 was done, some micro-benchmarks were run, and @shipilev noticed a regression in C1 with constant null handling:
> http://cr.openjdk.java.net/~shade/8150921/notes.txt
> Looking over the code review:
> https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2016-May/022767.html
> I don't see any references to benchmark testing that would check for any regressions in the InlineUnsafeOps + OptimizeUnsafes optimization that 8150921 mostly bypassed. @vidmik
> Now this PR proposes to remove this mostly dead code. I'm OK with that, since blindly reviving it risks hitting bitrot, but for compleness, perhaps we should file 2 followup RFEs:
> 
> 1. investigate constant null C1 regression
> 2. measure if the dead InlineUnsafeOps + OptimizeUnsafes optimization is worth reviving in a later release (with sufficient bake time)

They are indeed necessary. Thanks for sharing more information about JDK-8150921. I've filed JDK-8267783 and JDK-8267782 and assign them to me, I would investigate and check if it's worth doing later.

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PR: https://git.openjdk.java.net/jdk/pull/3917