WAST has directives to check that NaNs returned by tests have the correct bits: assert_return_arithmetic_nan and assert_return_canonical_nan. With the inclusion of SIMD instructions, these directives need to understand what type of vector is returned by a test to correctly check whether NaNs in the vector lanes are correct (e.g. an f32x4 filled with NaNs is different than an f64x2 filled with NaNs). There are two proposals out there for extending the directive:

• create new directives with the expected type appended to the name: e.g., (assert_return_arithmetic_nan_f32x4 (invoke ...))
• add an optional parameter to the directive: e.g., (assert_return_canonical_nan (invoke ...) f64x2)

I am raising the issue here to solicit comments before the SIMD spec tests are merged that require this feature. @Honry has worked on this in WAVM/WAVM#187 (see discusison by @AndrewScheidecker and @rossberg) and I have a PR ready to merge in bytecodealliance/wat#24. Please tag whoever else might have an opinion on the issue.