commit 3432d0a3e53896348d840176722be46d080ad439
author Boris Brezillon <boris.brezillon@collabora.com> Mon Oct 12 15:17:42 2020 +0200
committer Boris Brezillon <boris.brezillon@collabora.com> Thu Oct 15 08:05:23 2020 +0200
tree eb7e320d9b12bfc3b0c87505d4a7602ead4b21d8
parent 2f3f5da91dee2aa9727e7e2244a262584b0d9c02

pan/bi: Special-case BLEND instruction emission for blend shaders

Blend shaders shouldn't use the blend descriptors stored in the FAU RAM
since this is what triggered the blend shader call in the first place.
The descriptor is instead extracted from the compiler inputs and passed
as a constant to the blend instruction.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7151>

src/panfrost/bifrost/bifrost_compile.c

diff --git a/src/panfrost/bifrost/bifrost_compile.c b/src/panfrost/bifrost/bifrost_compile.c
index 1dbfa43..07a4bfe 100644
--- a/src/panfrost/bifrost/bifrost_compile.c
+++ b/src/panfrost/bifrost/bifrost_compile.c
@@ -168,7 +168,7 @@
 static void
 bi_emit_frag_out(bi_context *ctx, nir_intrinsic_instr *instr)
 {
-        if (!ctx->emitted_atest) {
+        if (!ctx->emitted_atest && !ctx->is_blend) {
                 bi_instruction ins = {
                         .type = BI_ATEST,
                         .src = {
@@ -197,29 +197,55 @@
                 .src = {
                         pan_src_index(&instr->src[0]),
                         BIR_INDEX_REGISTER | 60 /* Can this be arbitrary? */,
-                        /* Blend descriptor */
-                        BIR_INDEX_BLEND | BIFROST_SRC_FAU_LO,
-                        BIR_INDEX_BLEND | BIFROST_SRC_FAU_HI,
                 },
                 .src_types = {
                         nir_intrinsic_src_type(instr),
-                        nir_type_uint32
+                        nir_type_uint32,
+                        nir_type_uint32,
+                        nir_type_uint32,
                 },
                 .swizzle = {
                         { 0, 1, 2, 3 },
                         { 0 }
                 },
-                .dest = BIR_INDEX_REGISTER | 48 /* Looks like magic */,
                 .dest_type = nir_type_uint32,
                 .vector_channels = 4
         };
 
+        if (ctx->is_blend) {
+                /* Blend descriptor comes from the compile inputs */
+                blend.src[2] = BIR_INDEX_CONSTANT | 0;
+                blend.src[3] = BIR_INDEX_CONSTANT | 32;
+                blend.constant.u64 = ctx->blend_desc;
+
+                /* Put the result in r0 */
+                blend.dest = BIR_INDEX_REGISTER | 0;
+        } else {
+                /* Blend descriptor comes from the FAU RAM */
+                blend.src[2] = BIR_INDEX_BLEND | BIFROST_SRC_FAU_LO;
+                blend.src[3] = BIR_INDEX_BLEND | BIFROST_SRC_FAU_HI;
+
+                /* By convention, the return address is stored in r48 and will
+                 * be used by the blend shader to jump back to the fragment
+                 * shader when it's done.
+                 */
+                blend.dest = BIR_INDEX_REGISTER | 48;
+        }
+
         assert(blend.blend_location < 8);
         assert(ctx->blend_types);
         assert(blend.src_types[0]);
         ctx->blend_types[blend.blend_location] = blend.src_types[0];
 
         bi_emit(ctx, blend);
+
+        if (ctx->is_blend) {
+                /* Jump back to the fragment shader, return address is stored
+                 * in r48 (see above).
+                 */
+                bi_instruction *ret = bi_emit_branch(ctx);
+                ret->src[2] = BIR_INDEX_REGISTER | 48;
+        }
 }
 
 static bi_instruction