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f37abef4265768f386e817a3ead3df5401ef0ca6
ReSkate/External/luau/Bytecode/include/Luau/Sccp.h
T
AyeZeeBB 6d542536e1 Plugins: sandboxed Luau plugins in mods, phase 1 (the host, and the base, console and storage APIs) 
A mod with a reskate-plugin.json is a plugin: Luau scripts that run in their own VM, with only
the reskate API ReSkate registers for them. Luau 0.741 is vendored in External/luau (the VM and
compiler only: no native code generation, no loadstring, io or C modules).

- Limits: 64 MB of memory, 50 ms a call, 2 ms a tick on average (over it for 3 s stops it),
  more than 5 errors in 10 s stops it, 50 log lines a second. A plugin over a limit cannot catch
  it in a pcall and carry on.
- API: reskate.log, on (load, unload, tick, level_loaded, level_unloading), timers, the level,
  its own package's files and JSON, require inside the package; console.command and print
  ("console"); storage get, set, add and keys ("storage"), 1 MB in
  %LOCALAPPDATA%\ReSkate\Plugins\<mod>\storage.json.
- Found every 2 s among the mods mods.json leaves on: switching a mod, or changing a plugin's
  files, loads, unloads or reloads it without a restart. A package holding a program is refused.
- plugin list, commands, reload, off and on in the console. A plugin cannot take a name of
  ReSkate's own commands.
- Tests: DINGOSDK_BUILD_PLUGIN_TESTS, including plugins written to break the sandbox.
2026-10-19 11:55:27 -05:00

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// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
#pragma once
#include "Luau/Bytecode.h"
#include "Luau/BytecodeGraph.h"
#include "Luau/BytecodeUtils.h"
#include "Luau/BytecodeValidation.h"
#include "Luau/VecDeque.h"
#include "Luau/DenseHash.h"
#include <cstdint>
#include <optional>
#include <utility>
#include <math.h>
namespace Luau
{
namespace Bytecode
{
template<typename T>
bool bcCompare(T a, T b, BcCondition cond)
{
switch (cond)
{
case BcCondition::Equal:
return a == b;
case BcCondition::NotEqual:
return a != b;
case BcCondition::Less:
return a < b;
case BcCondition::NotLess:
return !(a < b);
case BcCondition::LessEqual:
return a <= b;
case BcCondition::NotLessEqual:
return !(a <= b);
default:
LUAU_ASSERT(!"Unsupported condition");
}
return false;
}
inline bool bcCompare(double a, double b, BcCondition cond)
{
// Note: redundant bool() casts work around invalid MSVC optimization that merges cases in this switch, violating IEEE754 comparison semantics
switch (cond)
{
case BcCondition::Equal:
return a == b;
case BcCondition::NotEqual:
return a != b;
case BcCondition::Less:
return a < b;
case BcCondition::NotLess:
return !bool(a < b);
case BcCondition::LessEqual:
return a <= b;
case BcCondition::NotLessEqual:
return !bool(a <= b);
default:
LUAU_ASSERT(!"Unsupported condition");
}
return false;
}
inline std::optional<double> evaluateNumberBinaryOp(double a, double b, LuauOpcode op)
{
switch (op)
{
case LuauOpcode::LOP_ADD:
return a + b;
case LuauOpcode::LOP_SUB:
return a - b;
case LuauOpcode::LOP_MUL:
return a * b;
case LuauOpcode::LOP_DIV:
return a / b;
case LuauOpcode::LOP_MOD:
return a - floor(a / b) * b;
case LuauOpcode::LOP_POW:
return pow(a, b);
case LuauOpcode::LOP_IDIV:
return floor(a / b);
default:
return std::nullopt;
}
}
// SCCP is generic over the constant representation
// Each instantiation inherits VmConstOps with the operations the pass needs to evaluate constants
struct VmConstOps
{
virtual std::optional<BcOp> evaluate(const BcOp& lhsOp, const BcOp& rhsOp, LuauOpcode op) const = 0;
virtual bool falsey(const BcOp& falseyOp) const = 0;
virtual bool compare(const BcOp& lhsOp, const BcOp& rhsOp, BcCondition cond) const = 0;
virtual BcOp makeNil() const = 0;
virtual BcOp makeImmBool(bool value) const = 0;
// true if the VmConst supports ordering comparisons (number, integer, string)
virtual bool isOrderable(const BcOp& vmConstOp) const = 0;
virtual bool kindEquals(const BcOp& lhsOp, const BcOp& rhsOp) const = 0;
// true if operands represent the same value exactly (NaN == NaN is true)
virtual bool fullyequal(const BcOp& lhsOp, const BcOp& rhsOp) const = 0;
// returns std::nullopt if the comparison is not supported
virtual std::optional<bool> eq(const BcOp& lhsOp, const BcOp& rhsOp) const = 0;
virtual bool isNil(const BcOp& op) const = 0;
virtual bool isBoolean(const BcOp& op) const = 0;
virtual bool isNumber(const BcOp& op) const = 0;
virtual bool asBoolean(const BcOp& op) const = 0;
virtual double asNumber(const BcOp& op) const = 0;
virtual BcRef<BcImm> asImm(BcOp op) const = 0;
VmConstOps() = default;
virtual ~VmConstOps() = default;
VmConstOps(const VmConstOps&) = default;
VmConstOps(VmConstOps&&) = delete;
VmConstOps& operator=(const VmConstOps&) = default;
VmConstOps& operator=(VmConstOps&&) = delete;
};
struct BcVmConstImpl : public VmConstOps
{
std::optional<BcOp> evaluate(const BcOp& lhsOp, const BcOp& rhsOp, LuauOpcode op) const override;
bool falsey(const BcOp& falseyOp) const override;
bool compare(const BcOp& lhsOp, const BcOp& rhsOp, BcCondition cond) const override;
BcOp makeNil() const override;
BcOp makeImmBool(bool value) const override;
bool isOrderable(const BcOp& op) const override;
bool kindEquals(const BcOp& lhsOp, const BcOp& rhsOp) const override;
bool fullyequal(const BcOp& lhsOp, const BcOp& rhsOp) const override;
std::optional<bool> eq(const BcOp& lhsOp, const BcOp& rhsOp) const override;
bool isNil(const BcOp& op) const override;
bool isBoolean(const BcOp& op) const override;
bool isNumber(const BcOp& op) const override;
bool asBoolean(const BcOp& op) const override;
double asNumber(const BcOp& op) const override;
BcRef<BcImm> asImm(BcOp op) const override;
explicit BcVmConstImpl(BcFunction<BcVmConst>& func)
: VmConstOps()
, func(func)
{
}
BcFunction<BcVmConst>& func;
};
enum class Constness
{
Undetermined, // lattice top
NotAConstant, // lattice bottom
Constant,
};
struct ConstnessLattice
{
Constness kind = Constness::Undetermined;
std::optional<BcOp> constant = std::nullopt;
ConstnessLattice() = default;
ConstnessLattice(Constness kind, BcOp bcOp)
: kind(kind)
, constant(bcOp)
{
LUAU_ASSERT(kind == Constness::Constant);
}
explicit ConstnessLattice(Constness kind)
: kind(kind)
, constant(std::nullopt)
{
}
ConstnessLattice merge(VmConstOps* impl, const ConstnessLattice& other) const
{
// Undetermined is lattice top: meeting with it yields the other operand
if (kind == Constness::Undetermined)
return other;
if (other.kind == Constness::Undetermined)
return *this;
// two equal constants meet to themselves; anything else falls to bottom
if (equal(impl, other))
return *this;
return ConstnessLattice(Constness::NotAConstant);
}
bool equal(VmConstOps* impl, const ConstnessLattice& other) const
{
if (kind != other.kind)
return false;
if (kind == Constness::Constant)
return impl->fullyequal(constant.value(), other.constant.value());
return true;
}
};
enum class ConditionState
{
AlwaysFalse,
AlwaysTrue,
Unknown,
};
struct JumpTarget
{
bool dead = false;
BcOp blockOp;
ConditionState condition = ConditionState::Unknown;
};
using OpConstness = DenseHashMap<BcOp, ConstnessLattice, BcOpHash>;
struct SccpState
{
OpConstness opConstness;
ConstnessLattice operandLattice(const BcOp& op)
{
if (op.kind == BcOpKind::Proj || op.kind == BcOpKind::VmReg || op.kind == BcOpKind::VmUpvalue)
return ConstnessLattice(Constness::NotAConstant);
return opConstness[op];
}
// an unresolved condition is bottom if any operand is bottom, else top
Constness unknownConditionConstness(std::initializer_list<BcOp> ops)
{
for (const BcOp& op : ops)
{
ConstnessLattice lat = operandLattice(op);
if (lat.kind == Constness::NotAConstant)
return Constness::NotAConstant;
}
return Constness::Undetermined;
}
};
class SccpInterpreter
{
public:
explicit SccpInterpreter(VmConstOps* impl, SccpState* state)
: impl(impl)
, state(state)
{
}
ConditionState evaluateCondition(const BcOp& op);
ConditionState evaluateComparisonCondition(LuauOpcode op, const BcOp& lhs, const BcOp& rhs);
ConditionState evaluateXeqkCondition(BcRef<BcInst> inst);
ConstnessLattice evaluateArith(LuauOpcode op, BcRef<BcInst> instRepr);
ConstnessLattice evaluate(LuauOpcode op, BcRef<BcInst> instRepr);
private:
VmConstOps* impl;
SccpState* state;
};
template<typename VmConst>
struct Sccp
{
BcFunction<VmConst>& func;
VmConstOps* impl;
SccpState state;
SccpInterpreter interpreter;
// this maps a block (index) to its predecessors that it was reached from
// if a block is not in this map, it is unreachable
DenseHashMap<uint32_t, DenseHashSet<BcOp, BcOpHash>> blockUses;
VecDeque<BcOp> flowWorklist;
DenseHashSet<BcOp, BcOpHash> flowWorklistSet;
// when a def's lattice value changes, its uses must be re-evaluated
VecDeque<BcOp> ssaWorklist;
explicit Sccp(BcFunction<VmConst>& func, VmConstOps* impl)
: func(func)
, impl(impl)
, interpreter(impl, &state)
{
}
std::optional<BcOp> getFallthrough(BcRef<BcBlock> block)
{
std::optional<BcOp> fallthrough;
for (auto& succOp : block->successors)
{
if (succOp.kind == BcBlockEdgeKind::Fallthrough)
{
if (fallthrough)
{
LUAU_ASSERT(!"Multiple fallthroughs");
return std::nullopt;
}
fallthrough = succOp.target;
}
}
return fallthrough;
}
// builds the target/fallthrough pair for a two-way branch
// targetTakenOnTrue says which edge the jump takes when the condition holds; the untaken edge is marked dead when the condition resolves
// a cond of Unknown leaves both edges live, which also covers branches whose condition the pass never folds (loops, CMPPROTO)
std::vector<JumpTarget> conditionalTargets(BcRef<BcInst> inst, const BcOp& target, ConditionState cond, bool targetTakenOnTrue)
{
LUAU_ASSERT(target.kind == BcOpKind::Block);
std::optional<BcOp> fallthrough = getFallthrough(func.block(inst->block));
LUAU_ASSERT(fallthrough);
bool targetDead = false;
bool fallthroughDead = false;
if (cond == ConditionState::AlwaysTrue)
{
targetDead = !targetTakenOnTrue;
fallthroughDead = targetTakenOnTrue;
}
else if (cond == ConditionState::AlwaysFalse)
{
targetDead = targetTakenOnTrue;
fallthroughDead = !targetTakenOnTrue;
}
return {{targetDead, target, cond}, {fallthroughDead, *fallthrough, cond}};
}
// when the condition is a known constant, the untaken path is marked dead and each target carries its resolved condition
std::vector<JumpTarget> jumpTargets(BcRef<BcInst> inst)
{
switch (inst->op)
{
case LOP_JUMP:
case LOP_JUMPBACK:
{
const BcOp& targetOp = inst->ops[0];
LUAU_ASSERT(targetOp.kind == BcOpKind::Block);
return {{false, targetOp, ConditionState::AlwaysTrue}};
}
case LOP_JUMPIF:
case LOP_JUMPIFNOT:
{
ConditionState cond = interpreter.evaluateCondition(inst->ops[0]);
return conditionalTargets(inst, inst->ops[1], cond, inst->op == LOP_JUMPIF);
}
case LOP_JUMPIFEQ:
case LOP_JUMPIFLE:
case LOP_JUMPIFLT:
case LOP_JUMPIFNOTEQ:
case LOP_JUMPIFNOTLE:
case LOP_JUMPIFNOTLT:
{
ConditionState cond = interpreter.evaluateComparisonCondition(inst->op, inst->ops[0], inst->ops[1]);
return conditionalTargets(inst, inst->ops[2], cond, true);
}
case LOP_JUMPXEQKNIL:
case LOP_JUMPXEQKB:
case LOP_JUMPXEQKN:
case LOP_JUMPXEQKS:
{
ConditionState cond = interpreter.evaluateXeqkCondition(inst);
bool negated = func.immOp(inst->ops[1]).valueBoolean;
return conditionalTargets(inst, inst->ops[2], cond, !negated);
}
case LOP_FORNPREP:
case LOP_FORNLOOP:
return conditionalTargets(inst, inst->ops[3], ConditionState::Unknown, true);
case LOP_FORGPREP:
case LOP_FORGPREP_NEXT:
case LOP_FORGPREP_INEXT:
{
const BcOp& targetOp = inst->ops[3];
LUAU_ASSERT(targetOp.kind == BcOpKind::Block);
return {{false, targetOp, ConditionState::AlwaysTrue}};
}
case LOP_FORGLOOP:
// FORGLOOP has two leading imm operands FORGPREP* lack, so its target is ops[5]
return conditionalTargets(inst, inst->ops[5], ConditionState::Unknown, true);
case LOP_CMPPROTO:
return conditionalTargets(inst, inst->ops[2], ConditionState::Unknown, true);
case LOP_JUMPX:
LUAU_ASSERT(!"Should have never parsed this");
[[fallthrough]];
default:
return {};
}
}
// for each operand, evaluate and merge the lattice with the phi lattice
void visitPhi(BcRef<BcPhi> phi)
{
LUAU_ASSERT(phi->ops.size() > 0);
ConstnessLattice fold;
for (size_t i = 0; i < phi->ops.size(); i++)
{
BcOp op = phi->ops[i];
ConstnessLattice lattice = state.operandLattice(op);
fold = lattice.merge(impl, fold);
}
const ConstnessLattice& prevLattice = state.opConstness[phi.op];
if (!fold.equal(impl, prevLattice))
{
for (BcOp use : phi->uses)
ssaWorklist.push_back(use);
}
state.opConstness[phi.op] = fold;
}
// evaluate an instruction, comparing against the previous lattice value, and inserting all uses into the SSA worklist if it changed
void visitInst(BcRef<BcInst> inst)
{
// CAPTURE REF can be mutated externally via SETUPVAL
// the SSA graph doesn't model that alias, so mark the source non-constant to avoid folding a stale value
if (inst->op == LOP_CAPTURE && inst->ops.size() >= 2)
{
const BcOp& captureTypeOp = inst->ops[0];
LUAU_ASSERT(captureTypeOp.kind == BcOpKind::Imm);
const BcImm& captureImm = func.immOp(captureTypeOp);
if (captureImm.kind == BcImmKind::Int && captureImm.valueInt == LCT_REF)
{
const BcOp& srcOp = inst->ops[1];
ConstnessLattice prev = state.opConstness[srcOp];
if (prev.kind != Constness::NotAConstant && (srcOp.kind == BcOpKind::Inst || srcOp.kind == BcOpKind::Phi))
{
state.opConstness[srcOp] = ConstnessLattice(Constness::NotAConstant);
for (BcOp use : usesOf(func, srcOp))
ssaWorklist.push_back(use);
}
}
}
ConstnessLattice lattice = interpreter.evaluate(inst->op, inst);
const ConstnessLattice& prevLattice = state.opConstness[inst.op];
ConstnessLattice newVal = lattice.merge(impl, prevLattice);
if (!newVal.equal(impl, prevLattice))
{
for (BcOp use : inst->uses)
ssaWorklist.push_back(use);
}
for (const JumpTarget& target : jumpTargets(inst))
{
uint32_t blockIdx = func.getBlockIndex(func.blockOp(target.blockOp));
if (!target.dead)
{
blockUses[blockIdx].insert(inst->block);
if (!flowWorklistSet.find(target.blockOp))
flowWorklist.push_back(target.blockOp);
}
}
state.opConstness[inst.op] = newVal;
}
void propagate()
{
BcRef<BcBlock> entryBlock = func.block(func.entryBlock);
BcRef<BcBlock> exitBlock = func.block(func.exitBlock);
// the entry block is always live
blockUses[func.getBlockIndex(*entryBlock)].insert(entryBlock.op);
// the exit block is always live per serialization requirements
blockUses[func.getBlockIndex(*exitBlock)].insert(exitBlock.op);
flowWorklist.push_back(func.entryBlock);
while (!flowWorklist.empty() || !ssaWorklist.empty())
{
while (!flowWorklist.empty())
{
BcOp blockOp = flowWorklist.front();
BcRef<BcBlock> block = func.block(blockOp);
flowWorklist.pop_front();
if (flowWorklistSet.contains(block.op))
continue;
for (BcOp& phiOp : block->phis)
{
LUAU_ASSERT(phiOp.kind == BcOpKind::Phi);
visitPhi(func.phi(phiOp));
}
for (BcOp& op : block->ops)
{
LUAU_ASSERT(op.kind == BcOpKind::Inst);
visitInst(func.inst(op));
}
bool blockEndsWithBranch = false;
if (!block->ops.empty() && block->ops.back().kind == BcOpKind::Inst)
blockEndsWithBranch = !jumpTargets(func.inst(block->ops.back())).empty();
for (BcBlockEdge succEdge : block->successors)
{
if (succEdge.kind == BcBlockEdgeKind::Fallthrough)
{
uint32_t succIdx = func.getBlockIndex(func.blockOp(succEdge.target));
// If this block ends with a branch and the fallthrough wasn't already added by visitInst, skip it
if (blockEndsWithBranch && !blockUses[succIdx].contains(block.op))
continue;
blockUses[succIdx].insert(block.op);
if (!flowWorklistSet.contains(succEdge.target))
flowWorklist.push_back(succEdge.target);
}
}
flowWorklistSet.insert(block.op);
}
while (!ssaWorklist.empty())
{
BcOp op = ssaWorklist.front();
ssaWorklist.pop_front();
if (op.kind == BcOpKind::Inst)
visitInst(func.inst(op));
else if (op.kind == BcOpKind::Phi)
visitPhi(func.phi(op));
}
}
}
void replaceOperand(BcRef<BcInst> inst, BcOp oldOp, BcOp newOp)
{
for (BcOp& op : inst->ops)
{
if (op == oldOp)
op = newOp;
}
}
void replacePhiOperand(BcRef<BcPhi> phi, BcOp oldOp, BcOp newOp)
{
for (BcOp& op : phi->ops)
{
if (op == oldOp)
op = newOp;
}
}
bool isLoadInst(BcOp op)
{
if (op.kind != BcOpKind::Inst)
return false;
LuauOpcode opcode = func.inst(op)->op;
return opcode == LOP_LOADK || opcode == LOP_LOADKX || opcode == LOP_LOADN || opcode == LOP_LOADB || opcode == LOP_LOADNIL;
}
// rewrite a folded instruction in-place to a load instruction
// op identity is preserved so all existing uses remain valid
void rewriteToLoad(BcOp op, const ConstnessLattice& lattice)
{
BcRef<BcInst> inst = func.inst(op);
for (BcOp& usedOp : inst->ops)
{
func.eraseUse(op, usedOp);
}
inst->ops.clear();
if (lattice.kind == Constness::Constant)
{
BcOp op = lattice.constant.value();
if (op.kind == BcOpKind::Imm)
{
BcImm& imm = func.immOp(op);
if (imm.kind == BcImmKind::Boolean)
inst->op = LOP_LOADB;
else if (imm.kind == BcImmKind::Int)
inst->op = LOP_LOADN;
else
LUAU_ASSERT(!"unknown constant");
inst->ops.push_back(op);
}
else if (op.kind == BcOpKind::VmConst)
{
inst->op = LOP_LOADK;
inst->ops.push_back(op);
}
else
{
LUAU_ASSERT(!"unknown constant");
}
}
}
void removeDeadEdges(BcRef<BcInst> inst)
{
std::vector<JumpTarget> targets = jumpTargets(inst);
BcRef<BcBlock> block = func.block(inst->block);
BcOp liveTarget{};
bool hasLive = false;
for (const JumpTarget& target : targets)
{
if (target.dead)
{
BcEdges& succs = block->successors;
unsigned writeIdx = 0;
for (unsigned i = 0; i < succs.size(); i++)
{
if (!(succs[i].target == target.blockOp))
succs[writeIdx++] = succs[i];
}
succs.resize(writeIdx);
}
else
{
liveTarget = target.blockOp;
hasLive = true;
}
}
if (!hasLive)
return;
// ensure the live target has a fallthrough edge
bool hasFallthrough = false;
for (unsigned i = 0; i < block->successors.size(); i++)
{
if (block->successors[i].target == liveTarget)
{
block->successors[i].kind = BcBlockEdgeKind::Fallthrough;
hasFallthrough = true;
break;
}
}
if (!hasFallthrough)
block->successors.push_back({BcBlockEdgeKind::Fallthrough, liveTarget});
}
void replaceUses()
{
for (auto& [op, lattice] : state.opConstness)
{
if (lattice.kind != Constness::Constant)
continue;
if (op.kind != BcOpKind::Inst)
continue;
if (isLoadInst(op))
continue;
BcRef<BcInst> inst = func.inst(op);
LUAU_ASSERT(inst->op != LOP_JUMPX);
// isJumpD is safe to use here because JUMPX is not parsed by the GraphParser
if (isJumpD(inst->op))
{
removeDeadEdges(inst);
func.eraseOp(op);
}
else
rewriteToLoad(op, lattice);
}
}
void simplifyPhis()
{
for (BcOp blockOp : flowWorklistSet)
{
BcRef<BcBlock> block = func.block(blockOp);
for (auto it = block->phis.begin(); it != block->phis.end();)
{
BcOp op = *it;
LUAU_ASSERT(op.kind == BcOpKind::Phi);
BcRef<BcPhi> phi = func.phi(op);
if (phi->ops.empty())
{
++it;
continue;
}
BcOp unique = phi->ops[0];
bool allSame = true;
for (size_t i = 1; i < phi->ops.size(); i++)
{
if (phi->ops[i] != unique)
{
allSame = false;
break;
}
}
if (!allSame)
{
++it;
continue;
}
for (BcOp use : usesOf(func, op))
{
if (use.kind == BcOpKind::Inst)
replaceOperand(func.inst(use), op, unique);
else if (use.kind == BcOpKind::Phi)
replacePhiOperand(func.phi(use), op, unique);
// `unique` can be VmReg(it can be param).
func.recordUse(unique, use);
}
phi->uses.clear();
for (BcOp operand : phi->ops)
func.eraseUse(op, operand);
phi->ops.clear();
it = block->phis.erase(it);
}
}
}
void updateBlockUses()
{
// mark dead blocks by forward reachability from entry, not by blockUses
// (which can miss blocks depending on worklist ordering)
DenseHashSet<uint32_t> reachable;
std::vector<uint32_t> worklist;
uint32_t entryIdx = func.getBlockIndex(*func.block(func.entryBlock));
uint32_t exitIdx = func.getBlockIndex(*func.block(func.exitBlock));
reachable.insert(entryIdx);
reachable.insert(exitIdx);
worklist.push_back(entryIdx);
while (!worklist.empty())
{
uint32_t idx = worklist.back();
worklist.pop_back();
BcBlock& blk = func.blocks[idx];
for (const BcBlockEdge& edge : blk.successors)
{
uint32_t succIdx = func.getBlockIndex(func.blockOp(edge.target));
if (!reachable.contains(succIdx))
{
reachable.insert(succIdx);
worklist.push_back(succIdx);
}
}
}
for (BcBlock& block : func.blocks)
{
uint32_t blockidx = func.getBlockIndex(block);
block.useCount = static_cast<uint32_t>(blockUses[blockidx].size());
if (!reachable.contains(blockidx))
block.flags |= BcBlockFlag::Dead;
}
}
static std::optional<LuauOpcode> arithToKOpcode(LuauOpcode op)
{
switch (op)
{
case LOP_ADD:
return LOP_ADDK;
case LOP_SUB:
return LOP_SUBK;
case LOP_MUL:
return LOP_MULK;
case LOP_DIV:
return LOP_DIVK;
case LOP_MOD:
return LOP_MODK;
case LOP_POW:
return LOP_POWK;
default:
return std::nullopt;
}
}
// pure value producers can be removed once nothing references their result
bool isPureProducer(LuauOpcode op) const
{
switch (op)
{
case LOP_LOADK:
case LOP_LOADKX:
case LOP_LOADN:
case LOP_LOADB:
case LOP_LOADNIL:
case LOP_GETUPVAL:
return true;
default:
return false;
}
}
std::optional<Reg> registerOf(BcOp op)
{
if (op.kind == BcOpKind::VmReg)
return static_cast<Reg>(op.index);
if (auto it = func.regs.find(op); it != func.regs.end())
return it->second;
return std::nullopt;
}
void eraseDeadProducer(BcOp op)
{
if (op.kind != BcOpKind::Inst)
return;
BcRef<BcInst> inst = func.inst(op);
if (!isPureProducer(inst->op))
return;
if (!inst->uses.empty())
return;
func.eraseOp(op);
}
// values that are known constant used in arithmetic operations can be turned into their KR or RK variants
// sub and div have both KR and RK
void arithToK()
{
for (BcBlock& block : func.blocks)
{
uint32_t blockidx = func.getBlockIndex(block);
if (blockUses[blockidx].empty())
continue;
std::vector<BcOp> toErase;
toErase.reserve(block.ops.size());
for (auto bcOpIt = block.ops.begin(); bcOpIt != block.ops.end(); ++bcOpIt)
{
BcOp& op = *bcOpIt;
BcRef<BcInst> inst = func.inst(op);
std::optional<LuauOpcode> kOpcode = arithToKOpcode(inst->op);
if (!kOpcode || inst->ops.size() != 2)
continue;
BcOp lhs = inst->ops[0];
BcOp rhs = inst->ops[1];
// we can safely assume that, at most, one of these can be a Constant
// if they both were constant, the arith would have been folded
ConstnessLattice lhsLat = state.operandLattice(lhs);
ConstnessLattice rhsLat = state.operandLattice(rhs);
BcOp nonConstantOp;
ConstnessLattice constantK;
bool rk = false;
auto isConstNumber = [&](const ConstnessLattice& lat) -> bool
{
// Only VmConst are allowed because we don't want to fold a 'compact' LOADN into Tvalue constant
return lat.kind == Constness::Constant && lat.constant && lat.constant->kind == BcOpKind::VmConst &&
impl->isNumber(*lat.constant);
};
if (isConstNumber(rhsLat) && lhsLat.kind == Constness::NotAConstant)
{
// can fold this to a <ARITH>K variant
nonConstantOp = lhs;
constantK = rhsLat;
}
else if (isConstNumber(lhsLat) && rhsLat.kind == Constness::NotAConstant)
{
if (inst->op != LOP_ADD && inst->op != LOP_MUL && inst->op != LOP_SUB && inst->op != LOP_DIV)
continue;
nonConstantOp = rhs;
constantK = lhsLat;
if (inst->op == LOP_SUB)
{
kOpcode = LOP_SUBRK;
rk = true;
}
else if (inst->op == LOP_DIV)
{
kOpcode = LOP_DIVRK;
rk = true;
}
}
else
{
continue;
}
BcOp prevConstOperand = (nonConstantOp == lhs) ? rhs : lhs;
const bool constantIsRhs = (nonConstantOp == lhs);
// we can do some potential folding here now that we know one operand is constant
// for instance, adds of zero, muls of zero or 1, pows of zero or 1, etc
double valueNumber = impl->asNumber(constantK.constant.value());
if (valueNumber == 0)
{
if (inst->op == LOP_ADD || (inst->op == LOP_SUB && constantIsRhs))
{
inst->op = LOP_MOVE;
func.setOps(op, inst, {nonConstantOp});
}
else if (inst->op == LOP_MUL)
{
inst->op = LOP_LOADN;
BcImm imm{BcImmKind::Int};
imm.valueInt = 0;
func.setOps(op, inst, {func.addImm(imm)});
}
else if (inst->op == LOP_POW && constantIsRhs)
{
// x ^ 0 == 1 (0 ^ x is not folded: it is 0 for x != 0)
inst->op = LOP_LOADN;
BcImm imm{BcImmKind::Int};
imm.valueInt = 1;
func.setOps(op, inst, {func.addImm(imm)});
}
}
else if (valueNumber == 1)
{
if (inst->op == LOP_MUL || (inst->op == LOP_POW && constantIsRhs) || (inst->op == LOP_DIV && constantIsRhs))
{
inst->op = LOP_MOVE;
func.setOps(op, inst, {nonConstantOp});
}
}
else
{
inst->op = *kOpcode;
if (!rk)
func.setOps(op, inst, {nonConstantOp, constantK.constant.value()});
else
// SUBRK and DIVRK expect B as the constant table index
func.setOps(op, inst, {constantK.constant.value(), nonConstantOp});
}
toErase.push_back(prevConstOperand);
}
for (BcOp op : toErase)
{
eraseDeadProducer(op);
}
}
}
void rewrite()
{
arithToK();
replaceUses();
simplifyPhis();
updateBlockUses();
}
};
template<typename VmConst>
void foldConstants(BcFunction<VmConst>& func, VmConstOps& impl)
{
Sccp<VmConst> sccp(func, &impl);
sccp.propagate();
sccp.rewrite();
}
} // namespace Bytecode
} // namespace Luau
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