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

[Dean Long]

On Fri, 7 May 2021 14:41:43 GMT, Yi Yang <yyang at openjdk.org> wrote:

> After JDK-8150921, most Unsafe{Get,Put}Raw intrinsic methods can be replaced by Unsafe{Get,Put}Object.
> 
> There is the only one occurrence where c1 refers UnsafeGetRaw among GraphBuilder::setup_osr_entry_block()
> 
> https://github.com/openjdk/jdk/blob/74fecc070a6462e6a2d061525b53a63de15339f9/src/hotspot/share/c1/c1_GraphBuilder.cpp#L3143-L3157
> 
> We can replace UnsafeGetRaw with UnsafeGetObject when setting up OSR entry block. After that, Unsafe{Get,Put}Raw can be completely removed  because no one refers to them.
> 
> (This patch actually does two things:
> 1. `Replace UnsafeGetRaw with UnsafeGetObject when setting up OSR entry block` This is the only occurrence where c1 refers UnsafeGetRaw
> 2. `Cleanup unused Unsafe{Get,Put}Raw code`
> They are related so I put it together, but I still want to hear your suggestions, I will separate them into two patches if you think it is more reasonable)
> 
> Thanks!
> Yang

Hi Yang.  If the OptimizeUnsafes feature was ever useful for UnsafeGetRaw, then maybe we should apply that optimization to the UnsafeGetObject-with-null-object case rather than removing the feature.  Could you try it?

Also, I can't find where the UnsafeGetObject implementation handles the unaligned/wide flags of UnsafeGetRaw.

It would be good to get this change reviewed by someone from GC, since UnsafeGetRaw uses the GC barrier interface to do its work.

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