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// SPDX-License-Identifier: GPL-3.0-or-later
#include "rcc/CodeGen/MachineDCE.h"
#include "rcc/CodeGen/InstructionDescriptor.h"
#include "rcc/CodeGen/LiveVariables.h"
#include "rcc/CodeGen/MachineBasicBlock.h"
#include "rcc/CodeGen/MachineFunction.h"
#include "rcc/CodeGen/MachineInstr.h"
#include "rcc/CodeGen/MachineOperand.h"
#include "rcc/CodeGen/MachineRegisterInfo.h"
#include "rcc/CodeGen/TargetDescription.h"
#include <optional>
#include <string>
#include <utility>
#include <vector>
namespace rcc {
namespace {
[[nodiscard]] const MachinePassContract &dceContract() {
static const MachinePassContract Contract = [] {
MachinePassContract Value{
.Name = "machine-dce",
.Requires = {MachineFunctionProperty::Selected},
.Sets = {},
.Clears = {},
.RequiredAnalyses = {},
.VerificationStage = PipelineStage::Selected,
};
Value.ThreadSafety = PassThreadSafety::ThreadSafe;
Value.DeclaredChanges = {MachinePassChange::Instructions, MachinePassChange::Operands,
MachinePassChange::Registers};
return Value;
}();
return Contract;
}
[[nodiscard]] bool hasProtectedAttachment(const MachineInstr &Instruction) noexcept {
return Instruction.flags().has(MachineInstrFlag::FrameSetup) ||
Instruction.flags().has(MachineInstrFlag::FrameDestroy) ||
Instruction.debugInstrNumber() != 0 || Instruction.preInstrSymbol().has_value() ||
Instruction.postInstrSymbol().has_value() || Instruction.heapAllocMarker().has_value() ||
Instruction.pcSections().has_value() || Instruction.mmra().has_value() ||
Instruction.cfiType().has_value() || Instruction.deactivationSymbol().has_value();
}
[[nodiscard]] Expected<std::optional<std::vector<Register>>>
deadDefinitions(MachineInstr &Instruction, MachineRegisterInfo &Registers,
const TargetDescription &Target) {
const InstructionDescriptor *Descriptor = Target.instructionDescriptor(Instruction.opcode());
if (Descriptor == nullptr) {
return makeUnexpected(ErrorCode::VerificationError,
"machine DCE encountered an instruction without a descriptor");
}
const InstructionFlags Flags = Descriptor->Flags;
if (Flags.has(InstructionFlag::Terminator) || Flags.has(InstructionFlag::Branch) ||
Flags.has(InstructionFlag::Call) || Flags.has(InstructionFlag::Return) ||
Flags.has(InstructionFlag::Barrier) || Flags.has(InstructionFlag::MayStore) ||
Flags.has(InstructionFlag::HasSideEffects) ||
Flags.has(InstructionFlag::UnmodeledSideEffects) || hasProtectedAttachment(Instruction)) {
return std::nullopt;
}
std::vector<Register> VirtualDefinitions;
bool HasDefinition = false;
for (const MachineOperand &Operand : Instruction.operands()) {
const Register *Reg = Operand.getIf<Register>();
if (Reg == nullptr || !Operand.isDef())
continue;
HasDefinition = true;
if (Operand.isUse() || Operand.tiedOperandIndex())
return std::nullopt;
if (Reg->isVirtual()) {
if (!Registers.useEmpty(*Reg, false))
return std::nullopt;
VirtualDefinitions.push_back(*Reg);
continue;
}
if (!Reg->isPhysical() || !Operand.registerFlags().has(RegisterOperandFlag::Dead)) {
return std::nullopt;
}
}
if (!HasDefinition)
return std::nullopt;
return VirtualDefinitions;
}
[[nodiscard]] Expected<void> clearDebugUses(MachineRegisterInfo &Registers, Register Reg) {
std::vector<MachineOperand *> Uses;
for (MachineOperand &Operand : Registers.useOperands(Reg, true)) {
if (Operand.isDebugUse())
Uses.push_back(&Operand);
}
for (MachineOperand *Operand : Uses) {
auto Cleared = Operand->setRegister(Register{});
if (!Cleared)
return std::unexpected(Cleared.error());
}
return {};
}
} // namespace
const MachinePassContract &MachineDCEPass::contract() const noexcept {
return dceContract();
}
Expected<MachinePassResult> MachineDCEPass::run(MachineFunction &Function,
const TargetDescription &Target,
MachineFunctionAnalysisManager &) {
return runImplementation(Function, Target);
}
Expected<MachinePassResult> MachineDCEPass::runImplementation(MachineFunction &Function,
const TargetDescription &Target) {
MachinePassResult Result;
MachineRegisterInfo &Registers = Function.registerInfo();
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
for (MachineBasicBlock *Block = Function.firstBlock(); Block != nullptr;
Block = Block->next()) {
for (MachineInstr *Instruction = Block->firstInstruction(); Instruction != nullptr;) {
MachineInstr *Next = Instruction->next();
auto Definitions = deadDefinitions(*Instruction, Registers, Target);
if (!Definitions)
return std::unexpected(Definitions.error());
if (!*Definitions) {
Instruction = Next;
continue;
}
std::vector<Register> DefinitionList =
std::move(*Definitions).value_or(std::vector<Register>{});
for (const Register Reg : DefinitionList) {
auto Cleared = clearDebugUses(Registers, Reg);
if (!Cleared)
return std::unexpected(Cleared.error());
}
auto Removed = Instruction->eraseFromParent();
if (!Removed)
return std::unexpected(Removed.error());
for (const Register Reg : DefinitionList) {
if (!Registers.useEmpty(Reg, true) || Registers.getUniqueVRegDef(Reg) != nullptr) {
return makeUnexpected(ErrorCode::InternalError,
"machine DCE left references to a removed definition");
}
auto Erased = Registers.eraseVirtualRegister(Reg);
if (!Erased)
return std::unexpected(Erased.error());
}
LocalChange = true;
Result.Changed = true;
Instruction = Next;
}
}
}
if (Result.Changed) {
if (Function.properties().has(MachineFunctionProperty::TracksLiveness)) {
auto Rebuilt = rebuildMachineLiveness(Function, Target);
if (!Rebuilt)
return std::unexpected(Rebuilt.error());
}
Result.Changes = {MachinePassChange::Instructions, MachinePassChange::Operands,
MachinePassChange::Registers};
Result.Preserved = PreservedAnalyses::none();
} else {
Result.Preserved = PreservedAnalyses::all();
}
return Result;
}
} // namespace rcc
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