Remove dead shader instruction cycles with linear liveness traversal

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

@@ -1,5 +1,7 @@
 #include "graphics/shader/recompiler/ir/passes/DeadCodeElimination.h"
 
+#include <algorithm>
+
 namespace Libs::Graphics::ShaderRecompiler::IR {
 
 void RemoveIdentities(const BlockList& blocks) {
@@ -18,23 +20,32 @@ void RemoveIdentities(const BlockList& blocks) {
 }
 
 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;
+	std::vector<Inst*> pending;
+	for (auto* block: blocks) {
+		for (auto& inst: *block) {
+			// Retained resource-planning instructions live outside the block list.
+			inst.live = inst.MayHaveSideEffects() || std::ranges::any_of(inst.Uses(),
+			    [](const Use& use) { return use.user->Parent() == nullptr; });
+			if (inst.live) pending.push_back(&inst);
+		}
+	}
+	while (!pending.empty()) {
+		const auto* inst = pending.back();
+		pending.pop_back();
+		for (size_t arg = 0; arg < inst->NumArgs(); ++arg) {
+			auto* input = inst->Arg(arg).TryInstruction();
+			if (input != nullptr && input->Parent() != nullptr && !input->live) {
+				input->live = true;
+				pending.push_back(input);
 			}
 		}
-	} while (changed);
+	}
+	// Unlink every dead operand before freeing nodes in a dead Phi cycle.
+	for (auto* block: blocks)
+		for (auto& inst: *block)
+			if (!inst.live) inst.Invalidate();
+	for (auto* block: blocks)
+		std::erase_if(block->Instructions(), [](const Inst& inst) { return !inst.live; });
 }
 
 } // namespace Libs::Graphics::ShaderRecompiler::IR