[clang] [clang] Macro for constant rounding mode (PR #92699)

[Joshua Cranmer via cfe-commits]

jcranmer-intel wrote:

Overall, I'm not opposed to this patch.

This new macro should probably be mentioned somewhere in the clang user documentation.

> The way this requirement is formulated indicates that it could be implemented using preprocessor facility. Such implementation would require a builtin macro that is set in the region where pragma FENV_ROUND is in effect and reflects constant rounding mode.

Has there been any discussion with gcc and libc implementations about how they plan to implement this requirement? I'm not entirely convinced this is the best approach, especially given that "`printf` and `scanf` families" is on the list of functions that need to be affected, and that's a decent amount of functions to have to wrap with round-mode-aware-variants.

> This change introduces macro ROUNDING_MODE, which is a string dependent on the constant rounding mode

It expands to an identify, not a string literal, right?

https://github.com/llvm/llvm-project/pull/92699