[jdk17u-dev] RFR: 8296545: C2 Blackholes should allow load optimizations [v2]

[Aleksey Shipilev]

On Mon, 24 Apr 2023 08:59:14 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Unclean backport to improve Blackhole performance and match it to released JDK 20.
>> The backport is unclean because there are two little conflicts:
>>   1. The context conflict in `MemBarNode::make`, where the `MemBarStoreStore` was moved to another place. I resolved the conflict by hand: accepted only the `Blackhole` case removal.
>>   2. IR Framework needs `MUL_I` constant for test to work.
>> 
>> Additional testing:
>>   - [x] macos-aarch64-server-fastdebug, `compiler/irTests/blackhole` (includes new test)
>>   - [x] Eyeballing perfasm outputs with/without this patch
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
> 
>  - Merge branch 'master' into JDK-8296545-blackhole-loads
>  - Backport eab0ada3a16a432fdfd1f0b8fceca149c725451b

There was a little conflict in `memnode.cpp` due to https://github.com/openjdk/jdk17u-dev/commit/e6e6bedf7b7898a88dedce79600a473832871e9c coming in first, I pulled and remerged.  This basically eliminates this part of the original difference: "The context conflict in MemBarNode::make, where the MemBarStoreStore was moved to another place. I resolved the conflict by hand: accepted only the Blackhole case removal."

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PR Comment: https://git.openjdk.org/jdk17u-dev/pull/1273#issuecomment-1522021287