RFR: 8317575: AArch64: C2_MacroAssembler::fast_lock uses rscratch1 for cmpxchg result

[Andrew Haley]

On Thu, 5 Oct 2023 08:08:31 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> Please review this removal a potentially problematic usage of rscratch1 in C2_MacroAssembler::fast_lock.

Ouch! Great catch.

Yes, this patch looks good. And it would indeed make sense to poison `rscratch1` on the slow path. I don't know if that worked by luck or the author of fast locking realized that `rscratch1` wasn't clobbered if the compare failed.

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PR Comment: https://git.openjdk.org/jdk/pull/16049#issuecomment-1748406038