Clang + LLVM-libc Sharing Code for Floating Point Operations

[michaelrj-google]

Proposed name for this project: Hand-Eye Coordination

This is a tracking issue for the overall effort.

Summary: Clang needs support for math functions on APFloat for two main uses - compile time constant folding, and providing constexpr builtins for libc++. We can't just call the host platform's libc since it may not match the behavior of the libc on the target platform. Based on Project Hand-In-Hand we hope to be able to reuse code from LLVM-libc for this purpose.

Current TODOs (edit as needed):

• Create an RFC for this project
  • Specify the utilities that clang needs, and explain how they're different from the standard libc interface
  • Explain the potential issues (e.g. runtime rounding modes, fast math)
  • Propose a design for how this will actually work
• update this list once we have a design

cc: @AaronBallman @lntue @nickdesaulniers @vonosmas

[llvmbot]

@llvm/issue-subscribers-libc

Author: Michael Jones (michaelrj-google)

Proposed name for this project: Hand-Eye Coordination

This is a tracking issue for the overall effort.

Summary: Clang needs support for math functions on APFloat for two main uses - compile time constant folding, and providing constexpr builtins for libc++. We can't just call the host platform's libc since it may not match the behavior of the libc on the target platform. Based on Project Hand-In-Hand we hope to be able to reuse code from LLVM-libc for this purpose.

Current TODOs (edit as needed):

• Create an RFC for this project
  • Specify the utilities that clang needs, and explain how they're different from the standard libc interface
  • Explain the potential issues (e.g. runtime rounding modes, fast math)
  • Propose a design for how this will actually work
• update this list once we have a design

cc: @AaronBallman @lntue @nickdesaulniers @vonosmas

[jcranmer-intel]

Summary: Clang needs support for math functions on APFloat for two main uses - compile time constant folding, and providing constexpr builtins for libc++. We can't just call the host platform's libc since it may not match the behavior of the libc on the target platform. Based on Project Hand-In-Hand we hope to be able to reuse code from LLVM-libc for this purpose.

It's more than just clang; llvm should be able to rely on it too. APFloat itself is mostly owned by LLVM rather than Clang.

[c8ef]

Summary: Clang needs support for math functions on APFloat for two main uses - compile time constant folding, and providing constexpr builtins for libc++. We can't just call the host platform's libc since it may not match the behavior of the libc on the target platform. Based on Project Hand-In-Hand we hope to be able to reuse code from LLVM-libc for this purpose.

It's more than just clang; llvm should be able to rely on it too. APFloat itself is mostly owned by LLVM rather than Clang.

It would be great if constant folding libcall could utilize these utilities instead of directly calling the host libc and checking each libcall to ensure there is no under/overflow.