[llvm] [ARM] Prevent use of the VFP calling convention when +soft-float is enabled (PR #221434)

[Chris Copeland via llvm-commits]

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chrisnc wrote:

Updated. I think it's expected; my understanding is that `+soft-float` means software floating-point in all respects, including the ABI. When you ask `clang` for `-mfloat-abi=hard -msoft-float`, the ABI is overridden to `soft` (in a way that doesn't cause the same problems as tweaking target features directly). I'm curious what specific behavior you would have in mind for `+soft-float` (as opposed to `float-abi`) on mve+nofp cores that couldn't be achieved by just choosing either the soft- or hard-float ABI.

https://github.com/llvm/llvm-project/pull/221434