@beetreeswrote

On 32-bit x86,the ABI specifies that f16 gets returned in xmm0, which is what Clang and GCC do (neither Clang nor GCC support _Float16 when SSE2 is disabled)

So... for the "Rust" ABI we can do our own thing bypassing this (likely similar fof32/f64, we should just always returnf16 in viaPassMode::Indirect), but what shall we do for theextern "C" ABI? We'll need a new dedicated compiler error (likely as part of the pass that we are addinghere) that rejects returningf16 when the SSE registers are not available.

That will mean that libcore does not compile on i586 targets.... Actually libcore uses the "Rust" ABI so that one is fine. But if we haveextern "C" float functions somewhere those would not be portable any more.

Cc@tgross35@chorman0773