shader: fix readlane/writelane for inactive host lanes

src/graphics/shader/recompiler/ir/ReadLaneElimination.h

@@ -0,0 +1,20 @@
+#ifndef EMULATOR_INCLUDE_EMULATOR_GRAPHICS_SHADER_RECOMPILER_READLANEELIMINATION_H_
+#define EMULATOR_INCLUDE_EMULATOR_GRAPHICS_SHADER_RECOMPILER_READLANEELIMINATION_H_
+
+#include "graphics/shader/recompiler/ir/ShaderIR.h"
+
+namespace Libs::Graphics::ShaderRecompiler::IR {
+
+struct ReadLaneEliminationStats {
+	uint32_t rewritten_reads = 0;
+	uint32_t shadow_writes   = 0;
+};
+
+// Replaces fixed-lane ReadLane operations that are reached by a matching WriteLane on every
+// control-flow path. A synthetic scalar register snapshots the value at WriteLane execution time,
+// so the rewrite remains valid when the source SGPR is subsequently overwritten.
+[[nodiscard]] ReadLaneEliminationStats EliminateReadLane(Program& program);
+
+} // namespace Libs::Graphics::ShaderRecompiler::IR
+
+#endif /* EMULATOR_INCLUDE_EMULATOR_GRAPHICS_SHADER_RECOMPILER_READLANEELIMINATION_H_ */