Fix pixel shader input aliases

src/graphics/shader/recompiler/backend/spirv/spirvEmitterModule.cpp

@@ -388,6 +388,19 @@ void DefineInputs(EmitterState& state) {
 		}
 	}
 	for (auto& input: state.inputs) {
+		if (state.program.stage == ShaderType::Pixel &&
+		    input.kind == IR::StageInputKind::Parameter) {
+			const auto location = PixelParameterLocation(state, input.location);
+			const auto alias = std::ranges::find_if(state.inputs, [&](const InputBinding& other) {
+				return other.kind == IR::StageInputKind::Parameter && other.variable_id != 0 &&
+				       PixelParameterLocation(state, other.location) == location;
+			});
+			if (alias != state.inputs.end()) {
+				EXIT_IF(alias->per_vertex != input.per_vertex);
+				input.variable_id = alias->variable_id;
+				continue;
+			}
+		}
 		uint32_t type = TypeU32(state);
 		switch (input.kind) {
 			case IR::StageInputKind::VertexIndex:

src/graphics/shader/recompiler/ir/passes/ShaderInfoCollection.cpp

@@ -226,6 +226,18 @@ void CollectPixelInputs(const Program& program, const ShaderPixelInputInfo* pixe
 			}
 		}
 	}
+	// Aliases of a vertex output share one SPIR-V interface variable. If any
+	// alias reads raw vertices, interpolate the other aliases from those too.
+	for (uint32_t input = 0; input < pixel->input_num; input++) {
+		for (uint32_t alias = 0; alias < pixel->input_num; alias++) {
+			if (ShaderPixelParameterMappedLocation(*pixel, input) ==
+			        ShaderPixelParameterMappedLocation(*pixel, alias) &&
+			    ShaderPixelParameterIsFlat(*pixel, input) ==
+			        ShaderPixelParameterIsFlat(*pixel, alias)) {
+				per_vertex[input] = per_vertex[input] || per_vertex[alias];
+			}
+		}
+	}
 	for (uint32_t input = 0; input < pixel->input_num; input++) {
 		AddInput(info, StageInputKind::Parameter, input, 4, fmt::format("in_param_{}", input),
 		         per_vertex[input]);