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In the past, multiple writes to a single register were pretty common, but since we've transitioned to NIR, and leave the IR in SSA form for everything not captured in a phi-web, the pattern of generating new temporary registers at each step is a lot more common. This pass isn't nearly as useful now. Across fossil-db on Alchemist, this affects only 0.55% of shaders, which fall into two cases: - Coarse pixel shading pixel-X/Y setup. There are a few cases where we write a partial calculation into a register, then have a second instruction read that as a source and overwrite it as a destination. While we could use a temporary here, it doesn't actually help with register pressure at all, since there's the same amount of values live at both instructions regardless. So while this pass kicks in, it doesn't do anything useful. - Geometry shader control data bits (5 shaders total). We track masks for handling EndPrimitive in a single register across the program, and apparently in some cases can split the live range. However, it's a single register...only in geometry shaders...which use EndPrimitive. None of them appear to be in danger of spilling, either. So this tiny benefit doesn't seem to justify the cost of running the pass. So, just throw it out. It's not worth keeping. Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com> Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26343>
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