[ruby-core:115945] [Ruby master Bug#19442] Remove USE_RINCGC flag

Issue #19442 has been updated by ko1 (Koichi Sasada). These kind of flags are provided to measure the impact with on/off the features. We can simulate them with parameters, but we can not avoid overhead of write barriers completely, for example. Anyway it was gone. ---------------------------------------- Bug #19442: Remove USE_RINCGC flag https://bugs.ruby-lang.org/issues/19442#change-105900 * Author: eightbitraptor (Matthew Valentine-House) * Status: Closed * Priority: Normal * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- [GitHub PR #7317](https://github.com/ruby/ruby/pull/7313) ~~Ruby doesn't compile when USE_RINCGC is disabled. It's also not being tested in CI. As @nobu has pointed out in comments on the PR, fixing it is simple.~~ This was fixed in [this commit](https://github.com/ruby/ruby/commit/21543ac86ce0b730c1381588d7dc9eb… I think we should remove `USE_RINCGC` entirely and always run with incremental GC enabled, because I don't think this flag is being actively used, and removing it will simplify the code and reduce the cognitive overhead of working with the GC. We have a precedent for this: `USE_RGENGC=0` was removed [in this commit](https://github.com/ruby/ruby/commit/62c2b8c74e47652fc5bbaf6150f4acd… almost 3 years ago. `USE_RINCGC=0` is in a similar state. It has been broken for almost a year (since [this commit](https://github.com/ruby/ruby/commit/dde164e968e382d50b07ad455946888…), and [disabled in CI for more than 2 years](https://github.com/ruby/ruby/commit/46d3ea2c2569e2e5a9ee3e7e206f07f0…. -- https://bugs.ruby-lang.org/