pan/bi: Lower phis to scalar

If we don't lower phis to scalar, when we go out of SSA, we can get vector
nir_registers. In particular, we can get code like:

   r0 = vec2 r0.y, r0.x

This code looks like a move, but is in fact a swap. The trivial lowering of vec2
would not work -- the following fails to swap correctly:

   r0.x = r0.y
   r0.y = r0.x

Currently, we generate temporaries to handle these cases. It's easy to move the
complexity to NIR, though, and we'll want to scalarize phis for SSA-based RA
anyway.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16585>

diff --git a/src/panfrost/bifrost/bifrost_compile.c b/src/panfrost/bifrost/bifrost_compile.c
index c48591e..e338c5e 100644 (file)
--- a/src/panfrost/bifrost/bifrost_compile.c
+++ b/src/panfrost/bifrost/bifrost_compile.c
@@ -4256,6 +4256,7 @@ bi_optimize_nir(nir_shader *nir, unsigned gpu_id, bool is_blend)
         }
 
         NIR_PASS(progress, nir, nir_lower_alu_to_scalar, bi_scalarize_filter, NULL);
+        NIR_PASS(progress, nir, nir_lower_phis_to_scalar, true);
         NIR_PASS(progress, nir, nir_opt_vectorize, bi_vectorize_filter, NULL);
         NIR_PASS(progress, nir, nir_lower_bool_to_bitsize);