/*
* For all guard instructions in trace, check to see if we can relax the
* destination type to something less specific. The GuardConstraints map
* contains information about what properties of the guarded type matter for
* each instruction. Returns true iff any changes were made to the trace.
*/
bool relaxGuards(const IRUnit& unit, const GuardConstraints& guards) {
FTRACE(1, "relaxing guards for trace {}\n", unit.main());
auto blocks = rpoSortCfg(unit);
Block* reflowBlock = nullptr;
for (auto* block : blocks) {
for (auto& inst : *block) {
if (!isGuardOp(inst.op())) continue;
auto it = guards.find(&inst);
auto constraint = it == guards.end() ? TypeConstraint() : it->second;
// TODO(t2598894): Support relaxing inner types
auto const oldType = inst.typeParam();
auto newType = relaxType(oldType, constraint.category);
if (constraint.knownType <= newType) {
// If the known type is at least as good as the relaxed type, we can
// replace the guard with an assert.
auto newOp = guardToAssert(inst.op());
FTRACE(1, "relaxGuards changing {}'s type to {}, op to {}\n",
inst, constraint.knownType, newOp);
inst.setTypeParam(constraint.knownType);
inst.setOpcode(newOp);
inst.setTaken(nullptr);
if (!reflowBlock) reflowBlock = block;
} else if (!oldType.equals(newType)) {
FTRACE(1, "relaxGuards changing {}'s type to {}\n", inst, newType);
inst.setTypeParam(newType);
if (!reflowBlock) reflowBlock = block;
}
}
}
if (reflowBlock) reflowTypes(reflowBlock, blocks);
return (bool)reflowBlock;
}
/*
* For all guard instructions in trace, check to see if we can relax the
* destination type to something less specific. The GuardConstraints map
* contains information about what properties of the guarded type matter for
* each instruction. If simple is true, guards will not be relaxed past
* DataTypeSpecific except guards which are relaxed all the way to
* DataTypeGeneric. Returns true iff any changes were made to the trace.
*/
bool relaxGuards(IRUnit& unit, const GuardConstraints& guards, bool simple) {
auto blocks = rpoSortCfg(unit);
auto changed = false;
for (auto* block : blocks) {
for (auto& inst : *block) {
if (!isGuardOp(inst.op())) continue;
auto it = guards.find(&inst);
auto constraint = it == guards.end() ? TypeConstraint() : it->second;
if (simple && constraint.category > DataTypeGeneric &&
constraint.category < DataTypeSpecific) {
constraint.category = DataTypeSpecific;
}
// TODO(t2598894): Support relaxing inner types
auto const oldType = inst.typeParam();
auto newType = relaxType(oldType, constraint.category);
if (constraint.knownType <= newType) {
// If the known type is at least as good as the relaxed type, we can
// replace the guard with an assert.
auto newOp = guardToAssert(inst.op());
auto newType = std::min(constraint.knownType, previousGuardType(&inst));
FTRACE(1, "relaxGuards changing {}'s type to {}, op to {}\n",
inst, newType, newOp);
assert(!hasEdges(newOp));
if (inst.hasEdges()) {
block->push_back(unit.gen(Jmp, inst.marker(), inst.next()));
}
inst.setTypeParam(newType);
inst.setOpcode(newOp);
changed = true;
} else if (!oldType.equals(newType)) {
FTRACE(1, "relaxGuards changing {}'s type to {}\n", inst, newType);
inst.setTypeParam(newType);
changed = true;
}
}
}
if (!changed) return false;
// Make a second pass to reflow types, with some special logic for loads.
FrameState state(unit);
for (auto* block : blocks) {
state.startBlock(block);
for (auto& inst : *block) {
state.setMarker(inst.marker());
visitLoad(&inst, state);
retypeDests(&inst);
state.update(&inst);
}
state.finishBlock(block);
}
return true;
}
/*
* For all guard instructions in unit, check to see if we can relax the
* destination type to something less specific. The GuardConstraints map
* contains information about what properties of the guarded type matter for
* each instruction. If simple is true, guards will not be relaxed past
* DataTypeSpecific except guards which are relaxed all the way to
* DataTypeGeneric. Returns true iff any changes were made to the trace.
*/
bool relaxGuards(IRUnit& unit, const GuardConstraints& guards, bool simple) {
Timer _t("optimize_relaxGuards");
splitCriticalEdges(unit);
auto blocks = rpoSortCfg(unit);
auto changed = false;
for (auto* block : blocks) {
for (auto& inst : *block) {
if (!isGuardOp(inst.op())) continue;
auto it = guards.find(&inst);
auto constraint = it == guards.end() ? TypeConstraint() : it->second;
FTRACE(2, "relaxGuards processing {} with constraint {}\n",
inst, constraint);
if (simple && constraint.category > DataTypeGeneric &&
constraint.category < DataTypeSpecific) {
constraint.category = DataTypeSpecific;
}
auto const oldType = inst.typeParam();
auto newType = relaxType(oldType, constraint);
// Sometimes we (legitimately) end up with a guard like this:
//
// t4:StkPtr = GuardStk<BoxedArr,0,<DataTypeGeneric,
// inner:DataTypeSpecific,
// Type::BoxedCell>> t2:StkPtr
//
// The outer category is DataTypeGeneric because we know from eval stack
// flavors that the top of the stack here is always boxed. The inner
// category is DataTypeSpecific, indicating we care what the inner type
// is, even though it's just a hint. If we treated this like any other
// guard, we would relax the typeParam to Type::Gen and insert an assert
// to Type::BoxedCell right after it. Unfortunately, this loses the hint
// that the inner type is Arr. Eventually we should have some side
// channel for passing around hints for inner ref types, but for now the
// best we can do is forcibly keep the guard around, preserving the inner
// type hint.
if (constraint.assertedType.isBoxed() &&
oldType < constraint.assertedType) {
auto relaxedInner = relaxInner(oldType, constraint);
if (relaxedInner < Type::BoxedCell && newType >= Type::BoxedCell) {
FTRACE(1, "relaxGuards changing newType to {}\n", newType);
newType = relaxedInner;
}
}
if (constraint.assertedType < newType) {
// If the asserted type is more specific than the new guarded type, set
// the guard to the relaxed type but insert an assert operation between
// the instruction and its dst. We go from something like this:
//
// t5:FramePtr = GuardLoc<Int, 4, <DataTypeGeneric,Int>> t4:FramePtr
//
// to this:
//
// t6:FramePtr = GuardLoc<Gen, 4> t4:FramePtr
// t5:FramePtr = AssertLoc<Int, 4> t6:FramePtr
auto* oldDst = inst.dst();
auto* newDst = unit.genDst(&inst);
auto* newAssert = [&] {
switch (inst.op()) {
case GuardLoc:
case CheckLoc:
return unit.genWithDst(oldDst,
guardToAssert(inst.op()),
inst.marker(),
*inst.extra<LocalId>(),
constraint.assertedType,
newDst);
case GuardStk:
case CheckStk:
return unit.genWithDst(oldDst,
guardToAssert(inst.op()),
inst.marker(),
*inst.extra<StackOffset>(),
constraint.assertedType,
newDst);
case CheckType:
return unit.genWithDst(oldDst,
guardToAssert(inst.op()),
inst.marker(),
constraint.assertedType,
newDst);
default: always_assert(false);
}
}();
FTRACE(1, "relaxGuards inserting {} between {} and its dst, "
"changing typeParam to {}\n",
*newAssert, inst, newType);
inst.setTypeParam(newType);
// Now, insert the assert after the guard. For control flow guards,
// this means inserting it on the next edge.
if (inst.isControlFlow()) {
auto* block = inst.next();
block->insert(block->skipHeader(), newAssert);
} else {
auto* block = inst.block();
auto it = block->iteratorTo(&inst);
++it;
block->insert(it, newAssert);
}
changed = true;
} else if (oldType != newType) {
FTRACE(1, "relaxGuards changing {}'s type to {}\n", inst, newType);
inst.setTypeParam(newType);
changed = true;
}
}
}
if (!changed) return false;
// Make a second pass to reflow types, with some special logic for loads.
FrameState state(unit);
for (auto* block : blocks) {
state.startBlock(block);
for (auto& inst : *block) {
state.setMarker(inst.marker());
copyProp(&inst);
visitLoad(&inst, state);
if (!removeGuard(unit, &inst, state)) {
retypeDests(&inst);
state.update(&inst);
}
}
state.finishBlock(block);
}
return true;
}