shader_recompiler: add SSA

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

@@ -0,0 +1,40 @@
+#include "graphics/shader/recompiler/ir/passes/DeadCodeElimination.h"
+
+namespace Libs::Graphics::ShaderRecompiler::IR {
+
+void RemoveIdentities(const BlockList& blocks) {
+	for (auto* block: blocks) {
+		auto& instructions = block->Instructions();
+		for (auto inst = instructions.begin(); inst != instructions.end();) {
+			if (inst->GetOpcode() != ValueOpcode::Identity) {
+				inst++;
+				continue;
+			}
+			const auto replacement = inst->Arg(0);
+			inst->ReplaceUsesWith(replacement, false);
+			inst = instructions.erase(inst);
+		}
+	}
+}
+
+void EliminateDeadCode(const BlockList& blocks) {
+	bool changed;
+	do {
+		changed = false;
+		for (auto block = blocks.rbegin(); block != blocks.rend(); block++) {
+			auto& instructions = (*block)->Instructions();
+			auto  inst         = instructions.end();
+			while (inst != instructions.begin()) {
+				--inst;
+				if (inst->HasUses() || inst->MayHaveSideEffects()) {
+					continue;
+				}
+				inst->Invalidate();
+				inst    = instructions.erase(inst);
+				changed = true;
+			}
+		}
+	} while (changed);
+}
+
+} // namespace Libs::Graphics::ShaderRecompiler::IR