RFR: JDK-8277139 Improve code readability in PredecessorValidator (c1_IR.cpp)

[Ludvig Janiuk]

On Mon, 15 Nov 2021 18:26:36 GMT, Ludvig Janiuk <duke at openjdk.java.net> wrote:

> Refactor PredecessorValidator, more or less applying the following:
> 
> declare variables where used
> redeclare instead of reuse variables
> move assert to a more logical place
> remove unused length variable
> inline variables where senseful
> split loops
> extract methods
> 
> this is done in preparation for work on optimizing IR::verify. IR::verify calls PredecessorValidator. If the work of PredecessorValidator is made clearer, it will be easier to reason about where IR::verify doesn't need to be called (or where a subset of it would suffice).

Tests https://mach5.us.oracle.com/mdash/jobs/opjaniuk-jdk-20211115-1831-26239975

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PR: https://git.openjdk.java.net/jdk/pull/6394