Tracking Issue for `fma4_target_feature`

The feature gate for the issue is #![feature(fma4_target_feature)].

This target feature allows using a slightly different instruction for fused multiply-add. It does not add any intrinsics. This target feature (but not this feature gate) is used in libm.

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Figure out ABI interactions and other possible blockers/concerns
• Final Comment Period (FCP)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

None at the moment

Implementation history

Start by reviewing the fma4_target_feature feature gate and its use in libm, then investigate the ABI interactions and other blockers listed in the tracking checklist. The work is complete when the ABI concerns are resolved, the Final Comment Period is completed, and a stabilization PR is opened.