llvm/llvm-project

Tracking progress for constexpr cmath (P0533R9, P1383R2)

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#139885 opened on May 14, 2025

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c++23c++26clang:frontenddocumentationgood first issuelibclibc++metaissue

Description

constexpr cmath papers (P0533R9, P1383R2 for C++23 and C++26 will take a while to implement.

As we plan to implement builtins in clang using llvm-libc' math functions, and then use that to implement libc++, it would be useful to have a page that tracks what builtins are implemented, what libc features are missing, and what is supported by libc++.

That would let

  • LLVM contributors coordinate more effectively
  • Let users know what they can use
  • Let other implementers synchronize (MSVC wants to use libc, and MSSTL wants to be clang compatible)

I'm not sure if the best place would be a GitHub issue or an RST file somewhere. Note that libc does an excellent job of tracking what they support https://libc.llvm.org/headers/math/index.html.

Contributor guide

Tech stack
cpp
Domain
documentationbackend
Issue type
documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++LLVM internalsconstexpr functions
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
5
Research direction
Create a tracking page (either a GitHub issue or an RST file) that lists which constexpr cmath functions have builtins implemented in clang using llvm libc, which libc features are missing, and which are supported by libc++. Reference the existing libc math support page (https://libc.llvm.org/headers/math/index.html) as a model. Review the 16 comments on the issue for additional context and requirements from maintainers.