Mesa (master): pan/bi: Skip ATEST for colour blit shaders

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Module: Mesa
Branch: master
Commit: accffda30d75ee1cbda95a7a3c577bfcb6415b2e
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=accffda30d75ee1cbda95a7a3c577bfcb6415b2e

Author: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Date:   Thu Feb 11 21:33:02 2021 -0500

pan/bi: Skip ATEST for colour blit shaders

Small win.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9002>

---

 src/panfrost/bifrost/bifrost_compile.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/panfrost/bifrost/bifrost_compile.c b/src/panfrost/bifrost/bifrost_compile.c
index e81f7757aa5..4b23cf11421 100644
--- a/src/panfrost/bifrost/bifrost_compile.c
+++ b/src/panfrost/bifrost/bifrost_compile.c
@@ -337,6 +337,19 @@ bi_emit_blend_op(bi_builder *b, bi_index rgba, nir_alu_type T, unsigned rt)
         b->shader->blend_types[rt] = T;
 }
 
+/* Blend shaders do not need to run ATEST since they are dependent on a
+ * fragment shader that runs it. Blit shaders may not need to run ATEST, since
+ * ATEST is not needed if early-z is forced, alpha-to-coverage is disabled, and
+ * there are no writes to the coverage mask. The latter two are satisfied for
+ * all blit shaders, so we just care about early-z, which blit shaders force
+ * iff they do not write depth or stencil */
+
+static bool
+bi_skip_atest(bi_context *ctx, bool emit_zs)
+{
+        return (ctx->is_blit && !emit_zs) || ctx->is_blend;
+}
+
 static void
 bi_emit_fragment_out(bi_builder *b, nir_intrinsic_instr *instr)
 {
@@ -370,7 +383,8 @@ bi_emit_fragment_out(bi_builder *b, nir_intrinsic_instr *instr)
          * value, but render target #0 might not be floating point. However the
          * alpha value is only used for alpha-to-coverage, a stage which is
          * skipped for pure integer framebuffers, so the issue is moot. */
-        if (!b->shader->emitted_atest && !b->shader->is_blend) {
+
+        if (!b->shader->emitted_atest && !bi_skip_atest(b->shader, emit_zs)) {
                 nir_alu_type T = nir_intrinsic_src_type(instr);
 
                 bi_index rgba = bi_src_index(&instr->src[0]);