Currently, brw_fs_precompile doesn't set compressed_multisample_layout_mask, leaving it at the default value of 0 (non-CMS). This is dumb. Virtually all multisampled color buffers on Gen7+ use the CMS layout, not UMS or IMS. So, basically every shader that uses a sampler2DMS type (including most of WebGL) will require a recompile. A better guess would be: - 1 for sampler2DMS on Gen7+ (0 on Gen6) - 0 for sampler2DMSShadow - 0 for non-MS sampler types. This should eliminate almost all recompiles due to compressed_multisample_layout_mask. To accomplish this, we may want to create a bitfield similar to SamplersUsed or ShadowSamplers...SamplerIsMSAA or such. Then the precompile could easily check it. Alternatively, we could stop using bitfields and walk a list of NIR uniforms. It should be pretty simple.
Ilia pointed out that there is no such thing as a sampler2DMSShadow. So you can happily ignore that :)
Assuming it works, here's a better idea: kill the field altogether. Just treat all surfaces like CMS. According to the docs: "If ld_mcs is issued on a surface with MCS disabled, this message returns zeros in all channels." I'm pretty sure it'll work for UMS and maybe even IMS. It's a bit of extra work in the shader for the non-CMS case, but most things are CMS anyway.
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