Sirraide 2b5f68a5f6 [Clang][C++23] Implement P1774R8: Portable assumptions (#81014) ...

This implements the C++23 `[[assume]]` attribute.

Assumption information is lowered to a call to `@llvm.assume`, unless the expression has side-effects, in which case it is discarded and a warning is issued to tell the user that the assumption doesn’t do anything. A failed assumption at compile time is an error (unless we are in `MSVCCompat` mode, in which case we don’t check assumptions at compile time).

Due to performance regressions in LLVM, assumptions can be disabled with the `-fno-assumptions` flag. With it, assumptions will still be parsed and checked, but no calls to `@llvm.assume` will be emitted and assumptions will not be checked at compile time.

2024-03-09 12:07:16 +01:00

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