RFR: 8336297: C2: Fix -Wzero-as-null-pointer-constant warnings in derived Node ctors

[Julian Waters]

On Fri, 12 Jul 2024 20:24:37 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change that removes some -Wzero-as-null-pointer-constant
> warnings (when enabled) in C2 code. The constructors for some classes derived
> from Node pass 0 as the first argument to the base class constructor. Since
> that parameter is a Node*, this triggers a warning.  Changing to pass nullptr
> removes the warning.
> 
> Testing: mach5 tier1

Marked as reviewed by jwaters (Committer).

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PR Review: https://git.openjdk.org/jdk/pull/20162#pullrequestreview-2176166981