[clang] [llvm] [ARM] Emit an error when the hard-float ABI is enabled but can't be used. (PR #111334)

[Chris Copeland via cfe-commits]

chrisnc wrote:

> There's quite a lot of test changes that I presume needed to make

FWIW, virtually all of the test changes were due to cases where LLVM would silently use soft-float despite the hard-float ABI being explicitly requested, which is exactly the incorrect behavior that this PR is meant to fix. The total number of affected test cases is fairly small.

> and at least the LTO use case looks like we don't want to require extra information.

The direct invocation of llvm-lto case without target information is one I will look into, however, this change was made again because llvm was generating code in a manner where the hard-float ABI was requested but couldn't be fulfilled. Anywhere that might be happening can lead to unsound ABI-mixing. To me the question is whether the equivalent of that command is invoked internally without the correct target information in typical usage of LTO driven by clang/lld. I'm inclined to say no, based on there being zero other test failures related to this change, but I will do some digging to understand the situation.

https://github.com/llvm/llvm-project/pull/111334