x86-32 "f16" ABI needs SSE, incompatible with i586 targets · Issue #131819 · rust-lang/rust (original) (raw)

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Description

@beetrees wrote

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 fo f32/f64, we should just always return f16 in via PassMode::Indirect), but what shall we do for the extern "C" ABI? We'll need a new dedicated compiler error (likely as part of the pass that we are adding here) that rejects returning f16 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 have extern "C" float functions somewhere those would not be portable any more.

Cc @tgross35 @chorman0773