RFR: 8255615: Zero: demote ZeroStack::abi_stack_available guarantee to assert

[Severin Gehwolf]

On Thu, 29 Oct 2020 19:13:06 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> It is currently `guarantee`, which slows down release bits unnecessarily. The affected method is private, and so what that `assert` really does is checks that no internal Zero code calls it with a wrong `thread` -- something that should be caught by `fastdebug` builds.
> 
> inline int ZeroStack::abi_stack_available(Thread *thread) const {
>   guarantee(Thread::current() == thread, "should run in the same thread");
> 
> On my TR 3970X, changing that `guarantee` to `assert` improves:
>  - Zero x86_64 release "make images" times from ~9.5 minutes to ~7.5 minutes
>  - Zero x86_64 release "make bootcycle-images" times from ~49 minutes to ~44 minutes
> 
> Attention @jerboaa and @gnu-andrew, who have to suffer through the Zero build times occasionally.

LGTM

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Marked as reviewed by sgehwolf (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/943