RFR: JDK-8258603 c1 IR::verify is expensive [v7]

[Ludvig Janiuk]

On Mon, 3 Jan 2022 09:44:41 GMT, Ludvig Janiuk <duke at openjdk.java.net> wrote:

>> IR::verify iterates the whole object graph. This proves costly when used in e.g. BlockMerger inside of iterations over BlockLists, leading to quadratic or worse complexities as a function of bytecode length. In several cases, only a few Blocks were changed, and there was no need to go over the whole graph, but until now there was no less blunt tool for verification than IR::verify.
>> 
>> This PR introduces IR::verify_local, intended to be used when only a defined set of blocks have been modified. As a complement, expand_with_neighbors provides a way to also capture the neighbors of the "modified set" ahead of modification, so that afterwards the appropriate asserts can be made on all blocks which might possibly have been changed. All this should let us remove the expensive IR::verify calls, while still performing equivalent (or stricter) assertions.
>> 
>> Some changes have been made in the verifiers along the way. Some amount of refactoring, and even added invariants (see validate_edge_mutiality).
>
> Ludvig Janiuk has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - whitespace
>  - fix on SSOT
>  - SSOT part 2

Whichever way the PRODUCT/ASSERT pendulum swings, what's for sure is that it needs to be consistent, so I decided to move it around "single source of truth"-style.

I'm not from the compiler team so I don't know the implications or the build process, but I'm surprised there isn't an answer to  "how do we want to guard debug code?" I need a clear decision and guideline from the compiler team here.

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PR: https://git.openjdk.java.net/jdk/pull/6850