Zebediah Figura (@zfigura) commented about tests/hlsl/intrinsic-override.shader_test:
-[pixel shader] +[pixel shader fail(sm>=6)]
float2 max(float2 a, float2 b)
So these fail because max(0.1, 0.2) is a float1 rather than a float2, but this doesn't say anything about whether the user-defined max() function is *ever* matched. It turns out that, surprisingly, it isn't, so it might be nice to rewrite the tests to show that explicitly.