From: "shyouhei (Shyouhei Urabe) via ruby-core" <ruby-core@...>
Date: 2024-07-11T23:53:57+00:00
Subject: [ruby-core:118574] [Ruby master Bug#20604] Performance regression in C++ extensions due to lack of optimization flags by default since Ruby 2.7

Issue #20604 has been updated by shyouhei (Shyouhei Urabe).

Status changed from Open to Rejected

This is NG.  Some OSes (if I remember correctly it was Arch when we found this) ship clang and g++ combination.  They happen to have -O3 in common but not everything.  It was a wrong idea first place for us to share $optflags.  There's nothing we can do here.  Please specify $CXXFLAGS individually.

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Bug #20604: Performance regression in C++ extensions due to lack of optimization flags by default since Ruby 2.7
https://bugs.ruby-lang.org/issues/20604#change-109099

* Author: ntkme (Natsuki Natsume)
* Status: Rejected
* ruby -v: ruby 3.3.3 (2024-06-12 revision f1c7b6f435) [arm64-darwin23]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
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I found a significant performance regression in `sassc` gem when comparing Ruby 2.6 and later, that the extension is running more than 10x slower.

I have tracked it down to this commit: https://github.com/ruby/ruby/commit/733aa2f8b578d03bbcb91d2f496b01e3b990c7e8

This commit removed all default CXXFLAGS from RbConfig that were previously set, including `$optflags`, which has `-O3`.

Many of the C++ extensions like sassc use extconf/mkmf to compile, and they have assumed optflags are already set for CXXFLAGS. Without `-O3` as part of the default, the extensions are compiled without any optimizations and thus become extremely slow.

It is difficult for a regular user to find out the reason of the slowness, nor to say figuring out how to override CXXFLAGS for a native extension.

I'm not sure what was the reason of the change, but I think we should at least set `$optflags` in CXXFLAGS by default.



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