Merge pull request #9126 from vonchenplus/revert-8068-shader-if-false

Revert "shader_recompiler/dead_code_elimination: Add DeadBranchElimination pass"

src/shader_recompiler/frontend/ir/microinstruction.cpp

@@ -325,11 +325,6 @@ void Inst::AddPhiOperand(Block* predecessor, const Value& value) {
     phi_args.emplace_back(predecessor, value);
 }
 
-void Inst::ErasePhiOperand(size_t index) {
-    const auto operand_it{phi_args.begin() + static_cast<ptrdiff_t>(index)};
-    phi_args.erase(operand_it);
-}
-
 void Inst::OrderPhiArgs() {
     if (op != Opcode::Phi) {
         throw LogicError("{} is not a Phi instruction", op);

src/shader_recompiler/frontend/ir/value.h

@@ -178,13 +178,9 @@ public:
 
     /// Get a pointer to the block of a phi argument.
     [[nodiscard]] Block* PhiBlock(size_t index) const;
-
     /// Add phi operand to a phi instruction.
     void AddPhiOperand(Block* predecessor, const Value& value);
 
-    // Erase the phi operand at the given index.
-    void ErasePhiOperand(size_t index);
-
     /// Orders the Phi arguments from farthest away to nearest.
     void OrderPhiArgs();
 

src/shader_recompiler/ir_opt/dead_code_elimination_pass.cpp

@@ -1,104 +1,24 @@
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
-#include <algorithm>
-
-#include <boost/container/small_vector.hpp>
-
 #include "shader_recompiler/frontend/ir/basic_block.h"
 #include "shader_recompiler/frontend/ir/value.h"
 #include "shader_recompiler/ir_opt/passes.h"
 
 namespace Shader::Optimization {
-namespace {
-template <bool TEST_USES>
-void DeadInstElimination(IR::Block* const block) {
-    // We iterate over the instructions in reverse order.
-    // This is because removing an instruction reduces the number of uses for earlier instructions.
-    auto it{block->end()};
-    while (it != block->begin()) {
-        --it;
-        if constexpr (TEST_USES) {
-            if (it->HasUses() || it->MayHaveSideEffects()) {
-                continue;
-            }
-        }
-        it->Invalidate();
-        it = block->Instructions().erase(it);
-    }
-}
-
-void DeletedPhiArgElimination(IR::Program& program, std::span<const IR::Block*> dead_blocks) {
-    for (IR::Block* const block : program.blocks) {
-        for (IR::Inst& phi : *block) {
-            if (!IR::IsPhi(phi)) {
-                continue;
-            }
-            for (size_t i = 0; i < phi.NumArgs(); ++i) {
-                if (std::ranges::find(dead_blocks, phi.PhiBlock(i)) == dead_blocks.end()) {
-                    continue;
-                }
-                // Phi operand at this index is an unreachable block
-                phi.ErasePhiOperand(i);
-                --i;
-            }
-        }
-    }
-}
-
-void DeadBranchElimination(IR::Program& program) {
-    boost::container::small_vector<const IR::Block*, 3> dead_blocks;
-    const auto begin_it{program.syntax_list.begin()};
-    for (auto node_it = begin_it; node_it != program.syntax_list.end(); ++node_it) {
-        if (node_it->type != IR::AbstractSyntaxNode::Type::If) {
-            continue;
-        }
-        IR::Inst* const cond_ref{node_it->data.if_node.cond.Inst()};
-        const IR::U1 cond{cond_ref->Arg(0)};
-        if (!cond.IsImmediate()) {
-            continue;
-        }
-        if (cond.U1()) {
-            continue;
-        }
-        // False immediate condition. Remove condition ref, erase the entire branch.
-        cond_ref->Invalidate();
-        // Account for nested if-statements within the if(false) branch
-        u32 nested_ifs{1u};
-        while (node_it->type != IR::AbstractSyntaxNode::Type::EndIf || nested_ifs > 0) {
-            node_it = program.syntax_list.erase(node_it);
-            switch (node_it->type) {
-            case IR::AbstractSyntaxNode::Type::If:
-                ++nested_ifs;
-                break;
-            case IR::AbstractSyntaxNode::Type::EndIf:
-                --nested_ifs;
-                break;
-            case IR::AbstractSyntaxNode::Type::Block: {
-                IR::Block* const block{node_it->data.block};
-                DeadInstElimination<false>(block);
-                dead_blocks.push_back(block);
-                break;
-            }
-            default:
-                break;
-            }
-        }
-        // Erase EndIf node of the if(false) branch
-        node_it = program.syntax_list.erase(node_it);
-        // Account for loop increment
-        --node_it;
-    }
-    if (!dead_blocks.empty()) {
-        DeletedPhiArgElimination(program, std::span(dead_blocks.data(), dead_blocks.size()));
-    }
-}
-} // namespace
 
 void DeadCodeEliminationPass(IR::Program& program) {
-    DeadBranchElimination(program);
+    // We iterate over the instructions in reverse order.
+    // This is because removing an instruction reduces the number of uses for earlier instructions.
     for (IR::Block* const block : program.post_order_blocks) {
-        DeadInstElimination<true>(block);
+        auto it{block->end()};
+        while (it != block->begin()) {
+            --it;
+            if (!it->HasUses() && !it->MayHaveSideEffects()) {
+                it->Invalidate();
+                it = block->Instructions().erase(it);
+            }
+        }
     }
 }