pan/bi: Preload r60/r61 for MSAA + blend shader

This is the sort of leakiness I hate about blend shaders. MSAA + blend shader is
somewhat obscure but gets hit in the CTS.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15586>

diff --git a/src/panfrost/bifrost/bifrost_compile.c b/src/panfrost/bifrost/bifrost_compile.c
index 7f6052d5c5e51a0b0efc872ddede46051451c7e3..ff8564ffd142a6e76c8ffe974d17f0f626260766 100644 (file)
--- a/src/panfrost/bifrost/bifrost_compile.c
+++ b/src/panfrost/bifrost/bifrost_compile.c
@@ -4304,6 +4304,20 @@ bi_compile_variant(nir_shader *nir,
         bi_block *first_block = list_first_entry(&ctx->blocks, bi_block, link);
         uint64_t preload = first_block->reg_live_in;
 
+        /* If multisampling is used with a blend shader, the blend shader needs
+         * to access the sample coverage mask in r60 and the sample ID in r61.
+         * Blend shaders run in the same context as fragment shaders, so if a
+         * blend shader could run, we need to preload these registers
+         * conservatively. There is believed to be little cost to doing so, so
+         * do so always to avoid variants of the preload descriptor.
+         *
+         * We only do this on Valhall, as Bifrost has to update the RSD for
+         * multisampling w/ blend shader anyway, so this is handled in the
+         * driver. We could unify the paths if the cost is acceptable.
+         */
+        if (nir->info.stage == MESA_SHADER_FRAGMENT && ctx->arch >= 9)
+                preload |= BITFIELD64_BIT(60) | BITFIELD64_BIT(61);
+
         info->ubo_mask |= ctx->ubo_mask;
         info->tls_size = MAX2(info->tls_size, ctx->info.tls_size);