dead_code_elimination_pass: Remove unreachable Phi arguments

This commit is contained in:
ameerj 2022-03-22 18:34:31 -04:00
parent f10d40a0a2
commit 67159e3be7
3 changed files with 36 additions and 0 deletions

View File

@ -326,6 +326,11 @@ 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);

View File

@ -179,9 +179,13 @@ 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();

View File

@ -2,6 +2,10 @@
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
#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"
@ -25,7 +29,26 @@ void DeadInstElimination(IR::Block* const block) {
}
}
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) {
@ -55,6 +78,7 @@ void DeadBranchElimination(IR::Program& program) {
case IR::AbstractSyntaxNode::Type::Block: {
IR::Block* const block{node_it->data.block};
DeadInstElimination<false>(block);
dead_blocks.push_back(block);
break;
}
default:
@ -66,6 +90,9 @@ void DeadBranchElimination(IR::Program& program) {
// Account for loop increment
--node_it;
}
if (!dead_blocks.empty()) {
DeletedPhiArgElimination(program, std::span(dead_blocks.data(), dead_blocks.size()));
}
}
} // namespace