shader: Support SSA loops on IR

src/shader_recompiler/frontend/ir/function.h

@@ -12,6 +12,7 @@ namespace Shader::IR {
 
 struct Function {
     BlockList blocks;
+    BlockList post_order_blocks;
 };
 
 } // namespace Shader::IR

src/shader_recompiler/frontend/ir/post_order.cpp

@@ -0,0 +1,48 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <boost/container/flat_set.hpp>
+#include <boost/container/small_vector.hpp>
+
+#include "shader_recompiler/frontend/ir/basic_block.h"
+#include "shader_recompiler/frontend/ir/post_order.h"
+
+namespace Shader::IR {
+
+BlockList PostOrder(const BlockList& blocks) {
+    boost::container::small_vector<Block*, 16> block_stack;
+    boost::container::flat_set<Block*> visited;
+
+    BlockList post_order_blocks;
+    post_order_blocks.reserve(blocks.size());
+
+    Block* const first_block{blocks.front()};
+    visited.insert(first_block);
+    block_stack.push_back(first_block);
+
+    const auto visit_branch = [&](Block* block, Block* branch) {
+        if (!branch) {
+            return false;
+        }
+        if (!visited.insert(branch).second) {
+            return false;
+        }
+        // Calling push_back twice is faster than insert on msvc
+        block_stack.push_back(block);
+        block_stack.push_back(branch);
+        return true;
+    };
+    while (!block_stack.empty()) {
+        Block* const block{block_stack.back()};
+        block_stack.pop_back();
+
+        if (!visit_branch(block, block->TrueBranch()) &&
+            !visit_branch(block, block->FalseBranch())) {
+            post_order_blocks.push_back(block);
+        }
+    }
+    return post_order_blocks;
+}
+
+} // namespace Shader::IR

src/shader_recompiler/frontend/ir/post_order.h

@@ -0,0 +1,13 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "shader_recompiler/frontend/ir/basic_block.h"
+
+namespace Shader::IR {
+
+BlockList PostOrder(const BlockList& blocks);
+
+} // namespace Shader::IR

src/shader_recompiler/frontend/maxwell/program.cpp

@@ -7,6 +7,7 @@
 #include <vector>
 
 #include "shader_recompiler/frontend/ir/basic_block.h"
+#include "shader_recompiler/frontend/ir/post_order.h"
 #include "shader_recompiler/frontend/ir/structured_control_flow.h"
 #include "shader_recompiler/frontend/maxwell/program.h"
 #include "shader_recompiler/frontend/maxwell/translate/translate.h"
@@ -56,11 +57,14 @@ IR::Program TranslateProgram(ObjectPool<IR::Inst>& inst_pool, ObjectPool<IR::Blo
     }
 
     fmt::print(stdout, "No optimizations: {}", IR::DumpProgram(program));
-    std::ranges::for_each(functions, Optimization::SsaRewritePass);
     for (IR::Function& function : functions) {
-        Optimization::Invoke(Optimization::GlobalMemoryToStorageBufferPass, function);
-        Optimization::Invoke(Optimization::ConstantPropagationPass, function);
-        Optimization::Invoke(Optimization::DeadCodeEliminationPass, function);
+        function.post_order_blocks = PostOrder(function.blocks);
+        Optimization::SsaRewritePass(function.post_order_blocks);
+    }
+    for (IR::Function& function : functions) {
+        Optimization::PostOrderInvoke(Optimization::GlobalMemoryToStorageBufferPass, function);
+        Optimization::PostOrderInvoke(Optimization::ConstantPropagationPass, function);
+        Optimization::PostOrderInvoke(Optimization::DeadCodeEliminationPass, function);
         Optimization::IdentityRemovalPass(function);
         Optimization::VerificationPass(function);
     }