clang-21.1.0 regression: Cannot select: intrinsic %llvm.coro.noop

[vogelsgesang]

Clang 21.1.0 crashes with the message

fatal error: error in backend: Cannot select: intrinsic %llvm.coro.noop

when compiling

#include <coroutine>

void x() {
    std::noop_coroutine();
}

with clang 21 and the flags -std=c++23 -O0 -stdlib=libc++.

https://godbolt.org/z/Gnb6Mvoao

The same code compiles in clang 20.1.0.

Note that the code compiles fine as soon as the same file contains an actual coroutine. Probably we skip the %llvm.coro.noop-lowering pass if the translation unit does not contain any coroutine

[llvmbot]

@llvm/issue-subscribers-coroutines

Author: Adrian Vogelsgesang (vogelsgesang)

Clang 21.1.0 crashes with the message

> fatal error: error in backend: Cannot select: intrinsic %llvm.coro.noop

when compiling

#include <coroutine>

void x() {
    std::noop_coroutine();
}

with clang 21 and the flags -std=c++23 -O0 -stdlib=libc++.

https://godbolt.org/z/Gnb6Mvoao

The same code compiles in clang 20.1.0.

Note that the code compiles fine as soon as the same file contains an actual coroutine. Probably we skip the %llvm.coro.noop-lowering pass if the translation unit does not contain any coroutine

[shafik]

CC @ChuanqiXu9 @rnk

[shafik]

This does not crash on trunk: https://godbolt.org/z/YWEbdWo3P

So I believe this may already be fixed, although not sure which patch fixed it.

[nikic]

/cherry-pick a647bb4