pan/bi: Document register conventions

Should motiviate RA decisions. Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9421>
2021-03-01 19:55:07 +00:00
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+# Bifrost compiler
+
+## Register file
+
+Defined partially in software, partially in hardware.
+
+## Blend shaders
+
+R0 - R3: input (color #0)
+R4 - R7: input (color #1)
+R8 - R15: general purpose
+R48: return address
+
+## Fragment
+
+Anything live during BLEND must respect blend shader registers.
+
+R0 - R3: preloaded (message #0)
+R4 - R7: preloaded (message #1)
+R57 - R63: preloaded (various)
+
+R0 - R15: general purpose (full threads)
+R48 - R63: general purpose (full threads)
+
+R32 - R47: general purpose (half threads, or v6)