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// SPDX-License-Identifier: GPL-3.0-or-later
#include "rcc/CodeGen/MachineMemoryFolding.h"
#include "rcc/CodeGen/InstructionDescriptor.h"
#include "rcc/CodeGen/MachineBasicBlock.h"
#include "rcc/CodeGen/MachineFunction.h"
#include "rcc/CodeGen/MachineFunctionCloner.h"
#include "rcc/CodeGen/MachineInstr.h"
#include "rcc/CodeGen/MachineMemOperand.h"
#include "rcc/CodeGen/MachineOperand.h"
#include "rcc/CodeGen/MachineRegisterInfo.h"
#include "rcc/CodeGen/TargetDescription.h"
#include "rcc/CodeGen/TargetMemoryFolding.h"
#include <algorithm>
#include <cstddef>
#include <optional>
#include <ranges>
#include <string>
#include <utility>
#include <vector>
namespace rcc {
namespace {
[[nodiscard]] const MachinePassContract &memoryFoldingContract() {
static const MachinePassContract Contract = [] {
MachinePassContract Value{
.Name = "machine-memory-folding",
.Requires = {MachineFunctionProperty::IsSSA, 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.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() ||
Instruction.flags().has(MachineInstrFlag::BundledWithPred) ||
Instruction.flags().has(MachineInstrFlag::BundledWithSucc);
}
struct FoldCandidate final {
MachineInstr *MemoryInstruction = nullptr;
MachineInstr *Consumer = nullptr;
Register DefinedRegister;
std::size_t ConsumerOperand = 0;
};
[[nodiscard]] std::optional<FoldCandidate> findCandidate(MachineInstr &Instruction,
MachineFunction &Function,
const TargetDescription &Target) {
const InstructionDescriptor *Descriptor = Target.instructionDescriptor(Instruction.opcode());
if (Descriptor == nullptr || !Descriptor->Flags.has(InstructionFlag::MayLoad) ||
Descriptor->Flags.has(InstructionFlag::MayStore) ||
Descriptor->Flags.has(InstructionFlag::Call) ||
Descriptor->Flags.has(InstructionFlag::Barrier) ||
Descriptor->Flags.has(InstructionFlag::UnmodeledSideEffects) ||
hasProtectedAttachment(Instruction) || Instruction.memOperands().empty()) {
return std::nullopt;
}
for (const MachineMemOperand *Memory : Instruction.memOperands()) {
if (Memory == nullptr || Memory->isStore() || Memory->isAtomic() || Memory->isVolatile()) {
return std::nullopt;
}
}
MachineOperand *Definition = nullptr;
Register DefinedRegister;
for (std::size_t Index = 0; Index < Instruction.operandCount(); ++Index) {
MachineOperand *Operand = Instruction.operandAt(Index);
const Register *Reg = Operand == nullptr ? nullptr : Operand->getIf<Register>();
if (Reg == nullptr || !Operand->isDef())
continue;
if (Definition != nullptr || !Reg->isVirtual())
return std::nullopt;
Definition = Operand;
DefinedRegister = *Reg;
}
if (Definition == nullptr || !Function.registerInfo().hasOneUse(DefinedRegister, true)) {
return std::nullopt;
}
MachineOperand *Use = nullptr;
for (MachineOperand &Candidate : Function.registerInfo().useOperands(DefinedRegister, false)) {
Use = &Candidate;
break;
}
MachineInstr *Consumer = Use == nullptr ? nullptr : Use->parent();
if (Consumer == nullptr || Consumer->parent() != Instruction.parent() ||
Instruction.next() != Consumer || hasProtectedAttachment(*Consumer) || Use->isImplicit() ||
Use->tiedOperandIndex()) {
return std::nullopt;
}
for (std::size_t Index = 0; Index < Consumer->operandCount(); ++Index) {
if (Consumer->operandAt(Index) == Use)
return FoldCandidate{&Instruction, Consumer, DefinedRegister, Index};
}
return std::nullopt;
}
[[nodiscard]] bool containsMemoryDescription(const MachineInstr &Instruction,
const MachineMemOperandDesc &Description) noexcept {
return std::ranges::any_of(Instruction.memOperands(),
[&Description](const MachineMemOperand *Memory) {
return Memory != nullptr && Memory->description() == Description;
});
}
[[nodiscard]] Expected<bool> applyFold(FoldCandidate Candidate, MachineFunction &Function,
const TargetDescription &Target,
const TargetMemoryFoldingInfo &Info) {
auto CanFold = Info.canFoldMemoryOperand(*Candidate.Consumer, Candidate.ConsumerOperand,
*Candidate.MemoryInstruction, Function, Target);
if (!CanFold)
return std::unexpected(CanFold.error());
if (!*CanFold)
return false;
std::vector<MachineMemOperandDesc> MemoryDescriptions;
for (const MachineMemOperand *Memory : Candidate.MemoryInstruction->memOperands()) {
if (Memory == nullptr) {
return makeUnexpected(ErrorCode::VerificationError,
"memory folding encountered a null memory operand");
}
MemoryDescriptions.push_back(Memory->description());
}
auto Folded = Info.foldMemoryOperand(*Candidate.Consumer, Candidate.ConsumerOperand,
*Candidate.MemoryInstruction, Function, Target);
if (!Folded)
return std::unexpected(Folded.error());
if (*Folded == nullptr || (*Folded)->parent() == nullptr ||
Candidate.MemoryInstruction->parent() != nullptr) {
return makeUnexpected(ErrorCode::VerificationError,
"target memory fold did not replace the consumer and erase the producer");
}
for (const MachineMemOperandDesc &Description : MemoryDescriptions) {
if (!containsMemoryDescription(**Folded, Description)) {
return makeUnexpected(ErrorCode::VerificationError,
"target memory fold did not migrate every memory operand");
}
}
auto FoldedSize = Info.getFoldedMemorySize(**Folded, Function, Target);
if (!FoldedSize)
return std::unexpected(FoldedSize.error());
if (!FoldedSize->has_value() || !FoldedSize->value().isKnown()) {
return makeUnexpected(ErrorCode::VerificationError,
"target folded instruction has no known folded memory size");
}
if (MemoryDescriptions.size() == 1 && MemoryDescriptions.front().Size.isKnown() &&
FoldedSize->value() != MemoryDescriptions.front().Size) {
return makeUnexpected(ErrorCode::VerificationError,
"target folded memory size disagrees with the migrated MMO");
}
if (!Function.registerInfo().useEmpty(Candidate.DefinedRegister, true) ||
Function.registerInfo().getUniqueVRegDef(Candidate.DefinedRegister) != nullptr) {
return makeUnexpected(ErrorCode::VerificationError,
"target memory fold retained the load result register");
}
auto Erased = Function.registerInfo().eraseVirtualRegister(Candidate.DefinedRegister);
if (!Erased)
return std::unexpected(Erased.error());
return true;
}
} // namespace
const MachinePassContract &MachineMemoryFoldingPass::contract() const noexcept {
return memoryFoldingContract();
}
Expected<MachinePassResult> MachineMemoryFoldingPass::run(MachineFunction &Function,
const TargetDescription &Target,
MachineFunctionAnalysisManager &) {
if (!Function.properties().containsAll(contract().Requires)) {
return makeUnexpected(ErrorCode::VerificationError,
"memory folding requires selected SSA MachineIR");
}
auto Trial = cloneMachineFunction(
Function, Target,
MachineFunctionCloneOptions{.NewStableID = Function.stableID(), .NewName = std::nullopt});
if (!Trial) {
return std::unexpected(
withErrorContext(Trial.error(), "memory folding transaction setup failed: "));
}
auto TrialResult = runImplementation(*Trial->ClonedFunction, Target);
if (!TrialResult)
return std::unexpected(TrialResult.error());
auto Result = runImplementation(Function, Target);
if (!Result) {
return std::unexpected(withErrorContext(
Result.error(), "memory folding diverged after a successful transaction preflight: "));
}
return Result;
}
Expected<MachinePassResult>
MachineMemoryFoldingPass::runImplementation(MachineFunction &Function,
const TargetDescription &Target) const {
MachinePassResult Result;
std::size_t FoldCount = 0;
bool LocalChange = true;
while (LocalChange && FoldCount < Options.MaximumFolds) {
LocalChange = false;
for (MachineBasicBlock *Block = Function.firstBlock(); Block != nullptr && !LocalChange;
Block = Block->next()) {
for (MachineInstr *Instruction = Block->firstInstruction(); Instruction != nullptr;
Instruction = Instruction->next()) {
std::optional<FoldCandidate> Candidate = findCandidate(*Instruction, Function, Target);
if (!Candidate)
continue;
auto Folded = applyFold(*Candidate, Function, Target, *Info);
if (!Folded)
return std::unexpected(Folded.error());
if (!*Folded)
continue;
++FoldCount;
Result.Changed = true;
LocalChange = true;
break;
}
}
}
if (Result.Changed) {
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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