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// SPDX-License-Identifier: GPL-3.0-or-later
#include "RegAllocGreedy.h"
#include "RegAllocBase.h"
#include "rcc/CodeGen/LiveIntervals.h"
#include "rcc/CodeGen/LiveRegMatrix.h"
#include "rcc/CodeGen/LiveVariables.h"
#include <algorithm>
#include <cstdint>
#include <limits>
#include <memory>
#include <optional>
#include <ranges>
#include <unordered_set>
#include <vector>
namespace rcc {
namespace {
struct EvictionCandidate final {
PhysicalRegister PhysicalReg;
std::vector<Register> Victims;
std::uint64_t Cost = 0;
};
[[nodiscard]] std::uint64_t saturatedAdd(std::uint64_t Left, std::uint64_t Right) noexcept {
if (Right > std::numeric_limits<std::uint64_t>::max() - Left)
return std::numeric_limits<std::uint64_t>::max();
return Left + Right;
}
[[nodiscard]] std::uint64_t normalizedSpillCost(const LiveInterval &Interval) noexcept {
std::uint64_t Length = 0;
for (const LiveSegment &Segment : Interval.MainRange.segments())
Length = saturatedAdd(Length, Segment.End.value() - Segment.Start.value());
Length = std::max<std::uint64_t>(1, Length);
constexpr std::uint64_t Scale = std::uint64_t{1} << 20U;
const std::uint64_t Weight = std::max<std::uint64_t>(1, Interval.SpillWeight);
const std::uint64_t ScaledWeight = Weight > std::numeric_limits<std::uint64_t>::max() / Scale
? std::numeric_limits<std::uint64_t>::max()
: Weight * Scale;
return std::max<std::uint64_t>(1, ScaledWeight / Length);
}
[[nodiscard]] bool isBetterEviction(const EvictionCandidate &Left,
const EvictionCandidate &Right) noexcept {
if (Left.Cost != Right.Cost)
return Left.Cost < Right.Cost;
if (Left.Victims.size() != Right.Victims.size())
return Left.Victims.size() < Right.Victims.size();
return Left.PhysicalReg.number() < Right.PhysicalReg.number();
}
class GreedyAllocatorEngine final : public RegAllocBase {
public:
GreedyAllocatorEngine(MachineFunction &Function, const TargetDescription &Target,
const TargetRegisterAllocationInfo &TargetInfo,
MachineFunctionAnalysisManager &Analyses, RegisterAllocationOptions Options)
: RegAllocBase(Function, Target, TargetInfo, Analyses, Options) {}
private:
[[nodiscard]] Expected<std::optional<EvictionCandidate>>
evictionCandidate(Register VirtualReg, PhysicalRegister Candidate,
const LiveIntervalsAnalysis::Result &Intervals, const LiveRegMatrix &Matrix,
const VirtRegMap &Mapping) const {
const LiveInterval *Current = Intervals.interval(VirtualReg);
if (Current == nullptr)
return std::optional<EvictionCandidate>{};
EvictionCandidate Result{.PhysicalReg = Candidate, .Victims = {}, .Cost = 0};
for (const RegisterInterference &Interference :
Matrix.collectInterferences(VirtualReg, Candidate)) {
if (Interference.Kind != RegisterInterferenceKind::VirtualRegister ||
!Interference.VirtualReg) {
return std::optional<EvictionCandidate>{};
}
const Register Victim = *Interference.VirtualReg;
if (std::ranges::find(Result.Victims, Victim) != Result.Victims.end())
continue;
if (!Mapping.isSpillable(Victim))
return std::optional<EvictionCandidate>{};
const LiveInterval *VictimInterval = Intervals.interval(Victim);
if (VictimInterval == nullptr)
return std::optional<EvictionCandidate>{};
Result.Victims.push_back(Victim);
Result.Cost = std::max(Result.Cost, normalizedSpillCost(*VictimInterval));
}
if (Result.Victims.empty())
return std::optional<EvictionCandidate>{};
const std::uint64_t CurrentCost = normalizedSpillCost(*Current);
if (Mapping.isSpillable(VirtualReg) && Result.Cost >= CurrentCost)
return std::optional<EvictionCandidate>{};
std::ranges::sort(Result.Victims, [](Register Left, Register Right) {
return Left.opaqueValue() < Right.opaqueValue();
});
return std::optional<EvictionCandidate>{std::move(Result)};
}
[[nodiscard]] Expected<AllocationRoundResult>
allocateRound(const LiveIntervalsAnalysis::Result &Intervals, VirtRegMap &Mapping) override {
LiveRegMatrix Matrix(Function, Target, Intervals);
AllocationRoundResult Result;
std::unordered_set<Register> Spilled;
std::vector<const LiveInterval *> Worklist = orderedAllocationIntervals(Intervals, Function);
std::ranges::stable_sort(Worklist, [&](const LiveInterval *Left, const LiveInterval *Right) {
const bool LeftSpillable = Mapping.isSpillable(Left->Reg);
const bool RightSpillable = Mapping.isSpillable(Right->Reg);
if (LeftSpillable != RightSpillable)
return !LeftSpillable;
if (Left->SpillWeight != Right->SpillWeight)
return Left->SpillWeight > Right->SpillWeight;
return false;
});
for (const LiveInterval *Interval : Worklist) {
const Register VirtualReg = Interval->Reg;
if (regalloc_detail::hasTerminatorDefinition(Function, Target, VirtualReg)) {
auto Marked = Mapping.setSpillable(VirtualReg, false);
if (!Marked)
return std::unexpected(Marked.error());
}
auto Candidates = regalloc_detail::allocationOrder(Function, Target, TargetInfo, VirtualReg);
if (!Candidates)
return std::unexpected(Candidates.error());
std::optional<PhysicalRegister> Assignment;
for (const PhysicalRegister Candidate : *Candidates) {
if (Matrix.checkInterference(VirtualReg, Candidate).Kind ==
RegisterInterferenceKind::Free) {
Assignment = Candidate;
break;
}
}
std::optional<EvictionCandidate> BestEviction;
if (!Assignment) {
for (const PhysicalRegister Candidate : *Candidates) {
auto CandidateEviction =
evictionCandidate(VirtualReg, Candidate, Intervals, Matrix, Mapping);
if (!CandidateEviction)
return std::unexpected(CandidateEviction.error());
if (!*CandidateEviction)
continue;
if (!BestEviction || isBetterEviction(**CandidateEviction, *BestEviction))
BestEviction = std::move(**CandidateEviction);
}
}
if (BestEviction) {
for (const Register Victim : BestEviction->Victims) {
auto Unassigned = Matrix.unassign(Victim);
if (!Unassigned)
return std::unexpected(Unassigned.error());
VirtRegMapEntry *Entry = Mapping.entry(Victim);
if (Entry == nullptr)
return makeUnexpected(ErrorCode::InternalError,
"greedy eviction found an unknown virtual register");
Entry->PhysicalReg.reset();
Entry->State = VirtRegAllocationState::Unassigned;
if (Spilled.insert(Victim).second)
Result.Spilled.push_back(Victim);
}
Assignment = BestEviction->PhysicalReg;
}
if (!Assignment) {
if (!Mapping.isSpillable(VirtualReg)) {
return makeUnexpected(ErrorCode::RegisterAllocationFailed,
"greedy allocator cannot assign a non-spillable virtual register");
}
if (Spilled.insert(VirtualReg).second)
Result.Spilled.push_back(VirtualReg);
continue;
}
auto MatrixAssignment = Matrix.assign(VirtualReg, *Assignment);
if (!MatrixAssignment)
return std::unexpected(MatrixAssignment.error());
auto MapAssignment = Mapping.assign(VirtualReg, *Assignment);
if (!MapAssignment)
return std::unexpected(MapAssignment.error());
}
return Result;
}
};
[[nodiscard]] const MachinePassContract &greedyContract() {
static const MachinePassContract Contract = [] {
MachinePassContract Value{
.Name = "greedy",
.Requires = {MachineFunctionProperty::NoPHIs, MachineFunctionProperty::TracksLiveness},
.Sets = {},
.Clears = {MachineFunctionProperty::IsSSA},
.RequiredAnalyses = {MachineFunctionAnalysisManager::id<LiveIntervalsAnalysis>(),
MachineFunctionAnalysisManager::id<VirtRegMapAnalysis>()},
.VerificationStage = std::nullopt,
};
Value.ThreadSafety = PassThreadSafety::ThreadSafe;
return Value;
}();
return Contract;
}
} // namespace
const MachinePassContract &GreedyAllocatorPass::contract() const noexcept {
return greedyContract();
}
Expected<MachinePassResult> GreedyAllocatorPass::run(MachineFunction &Function,
const TargetDescription &Target,
MachineFunctionAnalysisManager &Analyses) {
if (Info == nullptr)
return makeUnexpected(ErrorCode::InvalidArgument, "greedy allocator requires target behavior");
auto Trial = regalloc_detail::cloneForAllocation(Function, Target);
if (!Trial)
return std::unexpected(Trial.error());
const std::vector<PhysicalRegister> FunctionReserved =
regalloc_detail::functionReservedRegisters(Function, Target, *Info);
auto TrialReserved =
regalloc_detail::reserveFunctionRegisters(*Trial->ClonedFunction, FunctionReserved);
if (!TrialReserved)
return std::unexpected(TrialReserved.error());
MachineFunctionAnalysisManager TrialAnalyses;
auto Registered = registerStage11MachineAnalyses(TrialAnalyses);
if (!Registered)
return std::unexpected(Registered.error());
GreedyAllocatorEngine TrialAllocator(*Trial->ClonedFunction, Target, *Info, TrialAnalyses,
Options);
VirtRegMap TrialMapping(*Trial->ClonedFunction);
auto TrialRun = TrialAllocator.run(TrialMapping);
if (!TrialRun)
return std::unexpected(TrialRun.error());
auto TrialVerification =
regalloc_detail::verifyAllocationTrial(*Trial->ClonedFunction, Target, contract());
if (!TrialVerification)
return std::unexpected(TrialVerification.error());
auto Mapping = Analyses.getResult<VirtRegMapAnalysis>(Function, Target);
if (!Mapping)
return std::unexpected(Mapping.error());
GreedyAllocatorEngine Allocator(Function, Target, *Info, Analyses, Options);
auto Allocated = Allocator.run(**Mapping);
if (!Allocated) {
return std::unexpected(withErrorContext(
Allocated.error(), "greedy allocator diverged after a successful transaction preflight: "));
}
auto Reserved = regalloc_detail::reserveFunctionRegisters(Function, FunctionReserved);
if (!Reserved)
return std::unexpected(Reserved.error());
Allocated->Changed |= *Reserved;
MachinePassResult Result = regalloc_detail::passResult(*Allocated);
Result.Preserved.preserve<VirtRegMapAnalysis>();
return Result;
}
std::unique_ptr<MachineFunctionPass>
createGreedyAllocatorPass(const TargetRegisterAllocationInfo &Info,
RegisterAllocationOptions Options) {
return std::make_unique<GreedyAllocatorPass>(Info, Options);
}
} // namespace rcc
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