[clang] 21.1.0-rc2: compilation error due to misdetecting returning function as noreturn

[BtbN]

I'm not sure since when it is happening, but it's a recent addition to some RC that got used in https://github.com/mstorsjo/llvm-mingw
I didn't have time to fully bisect a version.

The error is:

/50-vvenc/source/Lib/CommonLib/Buffer.cpp:740:1: error: function declared 'noreturn' should not return [-Werror,-Winvalid-noreturn]

Referring to the relevant source here:
https://github.com/fraunhoferhhi/vvenc/blob/master/source/Lib/CommonLib/Buffer.cpp#L740
https://github.com/fraunhoferhhi/vvenc/blob/master/source/Lib/CommonLib/Buffer.h#L177

There is nothing indicating that this function is supposed to be noreturn.

My build script is doing nothing special for vvenc either, so this should be reproducable by just building vvenc with an affected clang version.
I'm targetting win-on-aarch64 with my builds, in case it does not happen on other arches.

cc @mstorsjo

[mstorsjo]

This seems to be fixed in latest git - I bisected the fix down to 22fef00 / #150003. So that fix should be backported to the 21.x release branch.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (BtbN)

I'm not sure since when it is happening, but it's a recent addition to some RC that got used in https://github.com/mstorsjo/llvm-mingw I didn't have time to fully bisect a version.

The error is:

/50-vvenc/source/Lib/CommonLib/Buffer.cpp:740:1: error: function declared 'noreturn' should not return [-Werror,-Winvalid-noreturn]

Referring to the relevant source here:
https://github.com/fraunhoferhhi/vvenc/blob/master/source/Lib/CommonLib/Buffer.cpp#L740
https://github.com/fraunhoferhhi/vvenc/blob/master/source/Lib/CommonLib/Buffer.h#L177

There is nothing indicating that this function is supposed to be noreturn.

My build script is doing nothing special for vvenc either, so this should be reproducable by just building vvenc with an affected clang version.
I'm targetting win-on-aarch64 with my builds, in case it does not happen on other arches.

cc @mstorsjo

[mstorsjo]

Backport request in #151752.

[mstorsjo]

I also reduced the original issue case down to this snippet:

#define THROW() throw
template <typename> struct AreaBuf {
  void calcVarianceSplit(const AreaBuf &, unsigned, int &, int &) const {
    THROW();
  }
};
template <>
void AreaBuf<short>::calcVarianceSplit(const AreaBuf &, unsigned, int &,
                                       int &) const {}

[brad0]

cc @MaskRay