2 files changed, 69 insertions, 0 deletions

diff --git a/src/shader_recompiler/ir_opt/layer_pass.cpp b/src/shader_recompiler/ir_opt/layer_pass.cpp
new file mode 100644
index 000000000..4574f7cf2
--- /dev/null
+++ b/src/shader_recompiler/ir_opt/layer_pass.cpp
@@ -0,0 +1,68 @@
+// SPDX-FileCopyrightText: Copyright 2022 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <algorithm>
+#include <bit>
+#include <optional>
+
+#include <boost/container/small_vector.hpp>
+
+#include "shader_recompiler/environment.h"
+#include "shader_recompiler/frontend/ir/basic_block.h"
+#include "shader_recompiler/frontend/ir/breadth_first_search.h"
+#include "shader_recompiler/frontend/ir/ir_emitter.h"
+#include "shader_recompiler/host_translate_info.h"
+#include "shader_recompiler/ir_opt/passes.h"
+#include "shader_recompiler/shader_info.h"
+
+namespace Shader::Optimization {
+
+static IR::Attribute EmulatedLayerAttribute(VaryingState& stores) {
+    for (u32 i = 0; i < 32; i++) {
+        if (!stores.Generic(i)) {
+            return IR::Attribute::Generic0X + (i * 4);
+        }
+    }
+    return IR::Attribute::Layer;
+}
+
+static bool PermittedProgramStage(Stage stage) {
+    switch (stage) {
+    case Stage::VertexA:
+    case Stage::VertexB:
+    case Stage::TessellationControl:
+    case Stage::TessellationEval:
+        return true;
+    default:
+        return false;
+    }
+}
+
+void LayerPass(IR::Program& program, const HostTranslateInfo& host_info) {
+    if (host_info.support_viewport_index_layer || !PermittedProgramStage(program.stage)) {
+        return;
+    }
+
+    const auto end{program.post_order_blocks.end()};
+    const auto layer_attribute = EmulatedLayerAttribute(program.info.stores);
+    bool requires_layer_emulation = false;
+
+    for (auto block = program.post_order_blocks.begin(); block != end; ++block) {
+        for (IR::Inst& inst : (*block)->Instructions()) {
+            if (inst.GetOpcode() == IR::Opcode::SetAttribute &&
+                inst.Arg(0).Attribute() == IR::Attribute::Layer) {
+                requires_layer_emulation = true;
+                inst.SetArg(0, IR::Value{layer_attribute});
+            }
+        }
+    }
+
+    if (requires_layer_emulation) {
+        program.info.requires_layer_emulation = true;
+        program.info.emulated_layer = layer_attribute;
+        program.info.stores.Set(IR::Attribute::Layer, false);
+        program.info.stores.Set(layer_attribute, true);
+    }
+}
+
+} // namespace Shader::Optimization
diff --git a/src/shader_recompiler/ir_opt/passes.h b/src/shader_recompiler/ir_opt/passes.h
index 586a0668f..11bfe801a 100644
--- a/src/shader_recompiler/ir_opt/passes.h
+++ b/src/shader_recompiler/ir_opt/passes.h
@@ -23,6 +23,7 @@ void RescalingPass(IR::Program& program);
 void SsaRewritePass(IR::Program& program);
 void PositionPass(Environment& env, IR::Program& program);
 void TexturePass(Environment& env, IR::Program& program, const HostTranslateInfo& host_info);
+void LayerPass(IR::Program& program, const HostTranslateInfo& host_info);
 void VerificationPass(const IR::Program& program);
 
 // Dual Vertex