shader_recompiler: add SSA

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

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <cstdint>
+
+namespace Libs::Graphics::ShaderRecompiler::IR {
+
+enum class ScalarReg : uint16_t {};
+enum class VectorReg : uint16_t {};
+
+// Architectural SGPRs occupy the low range. The current shader-only migration also accepts the
+// scalar shadow registers produced by Kyty's pre-existing read-lane pass; that pass disappears
+// once read-lane elimination operates on the SSA graph.
+constexpr uint32_t NumScalarRegs = 512;
+constexpr uint32_t NumVectorRegs = 256;
+
+constexpr uint32_t RegIndex(ScalarReg reg) {
+	return static_cast<uint32_t>(reg);
+}
+
+constexpr uint32_t RegIndex(VectorReg reg) {
+	return static_cast<uint32_t>(reg);
+}
+
+} // namespace Libs::Graphics::ShaderRecompiler::IR