SSATmp* TraceBuilder::preOptimizeDecRef(IRInstruction* inst) {
/*
* Refcount optimization:
*
* If the decref'ed value is guaranteed to be available after the decref,
* generate DecRefNZ instead of DecRef.
*
* This is safe WRT copy-on-write because all the instructions that
* could cause a COW return a new SSATmp that will replace the
* tracked state that we are using to determine the value is still
* available. I.e. by the time they get to the DecRef we won't see
* it in isValueAvailable anymore and won't convert to DecRefNZ.
*/
auto srcInst = inst->src(0)->inst();
while (srcInst->isPassthrough() && !srcInst->is(IncRef)) {
srcInst = srcInst->getPassthroughValue()->inst();
}
if (srcInst->is(IncRef)) {
if (m_state.isValueAvailable(srcInst->src(0))) {
inst->setOpcode(DecRefNZ);
}
}
return nullptr;
}
/**
* Trace back to the guard that provided the type of val, if
* any. Constrain it so its type will not be relaxed beyond the given
* DataTypeCategory. Always returns val, for convenience.
*/
SSATmp* TraceBuilder::constrainValue(SSATmp* const val, DataTypeCategory cat) {
if (!val) {
FTRACE(1, "constrainValue(nullptr, {}), bailing\n", cat);
return nullptr;
}
FTRACE(1, "constrainValue({}, {})\n", *val->inst(), cat);
// If cat is DataTypeGeneric, there's nothing to do.
if (cat == DataTypeGeneric) return val;
auto inst = val->inst();
if (inst->op() == LdLoc || inst->op() == LdLocAddr) {
// We've hit a LdLoc(Addr). If the source of the value is non-null and not
// a FramePtr, it's a real value that was killed by a Call. The value won't
// be live but it's ok to use it to track down the guard.
auto source = inst->extra<LdLocData>()->valSrc;
if (!source) {
// val was newly created in this trace. Nothing to constrain.
FTRACE(2, " - valSrc is null, bailing\n");
return val;
}
// If valSrc is a FramePtr, it represents the frame the value was
// originally loaded from. Look for the guard for this local.
if (source->isA(Type::FramePtr)) {
constrainLocal(inst->extra<LocalId>()->locId, source, cat,
"constrainValue");
return val;
}
// Otherwise, keep chasing down the source of val.
constrainValue(source, cat);
} else if (inst->op() == LdStack) {
constrainStack(inst->src(0), inst->extra<StackOffset>()->offset, cat);
} else if (inst->op() == CheckType) {
// Constrain this CheckType and keep going on its source value, in case
// there are more guards to constrain.
constrainGuard(inst, cat);
constrainValue(inst->src(0), cat);
} else if (inst->op() == StRef || inst->op() == StRefNT) {
// TODO(t2598894): This can be tightened up. As a conservative
// approximation, pass the constraint through to the source of the value.
constrainValue(inst->src(1), cat);
} else if (inst->isPassthrough()) {
constrainValue(inst->getPassthroughValue(), cat);
} else {
// Any instructions not special cased above produce a new value, so
// there's no guard for us to constrain.
FTRACE(2, " - value is new in this trace, bailing\n");
}
return val;
}
SSATmp* canonical(SSATmp* value) {
if (value == nullptr) return nullptr;
auto inst = value->inst();
while (inst->isPassthrough()) {
value = inst->getPassthroughValue();
inst = value->inst();
}
return value;
}
/**
* Trace back to the guard that provided the type of val, if
* any. Constrain it so its type will not be relaxed beyond the given
* DataTypeCategory. Returns true iff one or more guard instructions
* were constrained.
*/
bool IRBuilder::constrainValue(SSATmp* const val,
TypeConstraint tc) {
if (!shouldConstrainGuards()) return false;
if (!val) {
FTRACE(1, "constrainValue(nullptr, {}), bailing\n", tc);
return false;
}
FTRACE(1, "constrainValue({}, {})\n", *val->inst(), tc);
auto inst = val->inst();
if (inst->is(LdLoc, LdLocAddr)) {
// We've hit a LdLoc(Addr). If the source of the value is non-null and not
// a FramePtr, it's a real value that was killed by a Call. The value won't
// be live but it's ok to use it to track down the guard.
auto source = inst->extra<LocalData>()->typeSrc;
if (!source) {
// val was newly created in this trace. Nothing to constrain.
FTRACE(2, " - typeSrc is null, bailing\n");
return false;
}
// If valSrc is a FramePtr, it represents the frame the value was
// originally loaded from. Look for the guard for this local.
if (source->isA(Type::FramePtr)) {
return constrainLocal(inst->extra<LocalId>()->locId, source, tc,
"constrainValue");
}
// Otherwise, keep chasing down the source of val.
return constrainValue(source, tc);
} else if (inst->is(LdStack, LdStackAddr)) {
return constrainStack(inst->src(0), inst->extra<StackOffset>()->offset,
tc);
} else if (inst->is(CheckType, AssertType)) {
// If the dest type of the instruction fits the constraint we want, we can
// stop here without constraining any further. Otherwise, continue through
// to the source.
auto changed = false;
if (inst->is(CheckType)) changed = constrainGuard(inst, tc) || changed;
auto dstType = inst->typeParam();
if (!typeFitsConstraint(dstType, tc.category)) {
changed = constrainValue(inst->src(0), tc) || changed;
}
return changed;
} else if (inst->is(StRef)) {
// StRef requires that src(0) is boxed so we're relying on callers to
// appropriately constrain the values they pass to it. Any innerCat in tc
// should be applied to the value being stored.
tc.category = tc.innerCat;
tc.innerCat = DataTypeGeneric;
tc.assertedType = Type::Gen;
return constrainValue(inst->src(1), tc);
} else if (inst->is(Box, BoxPtr, Unbox, UnboxPtr)) {
// All Box/Unbox opcodes are similar to StRef/LdRef in some situations and
// Mov in others (determined at runtime), so we need to constrain both
// outer and inner.
auto maxCat = std::max(tc.category, tc.innerCat);
tc.category = maxCat;
tc.innerCat = maxCat;
tc.assertedType = Type::Gen;
return constrainValue(inst->src(0), tc);
} else if (inst->is(LdRef)) {
// Like StRef, we're relying on the caller to have appropriately
// constrained the outer type of the box. Constrain the inner type of the
// box with tc.
tc.innerCat = tc.category;
tc.category = DataTypeGeneric;
tc.assertedType = Type::Gen;
return constrainValue(inst->src(0), tc);
} else if (inst->isPassthrough()) {
return constrainValue(inst->getPassthroughValue(), tc);
} else {
// Any instructions not special cased above produce a new value, so
// there's no guard for us to constrain.
FTRACE(2, " - value is new in this trace, bailing\n");
return false;
}
// TODO(t2598894): Should be able to do something with LdMem<T> here
}
/**
* Trace back to the guard that provided the type of val, if
* any. Constrain it so its type will not be relaxed beyond the given
* DataTypeCategory. Returns true iff one or more guard instructions
* were constrained.
*/
bool TraceBuilder::constrainValue(SSATmp* const val,
TypeConstraint tc) {
if (!shouldConstrainGuards()) return false;
if (!val) {
FTRACE(1, "constrainValue(nullptr, {}), bailing\n", tc);
return false;
}
FTRACE(1, "constrainValue({}, {})\n", *val->inst(), tc);
auto inst = val->inst();
if (inst->is(LdLoc, LdLocAddr)) {
// We've hit a LdLoc(Addr). If the source of the value is non-null and not
// a FramePtr, it's a real value that was killed by a Call. The value won't
// be live but it's ok to use it to track down the guard.
auto source = inst->extra<LocalData>()->valSrc;
if (!source) {
// val was newly created in this trace. Nothing to constrain.
FTRACE(2, " - valSrc is null, bailing\n");
return false;
}
// If valSrc is a FramePtr, it represents the frame the value was
// originally loaded from. Look for the guard for this local.
if (source->isA(Type::FramePtr)) {
return constrainLocal(inst->extra<LocalId>()->locId, source, tc,
"constrainValue");
}
// Otherwise, keep chasing down the source of val.
return constrainValue(source, tc);
} else if (inst->is(LdStack, LdStackAddr)) {
return constrainStack(inst->src(0), inst->extra<StackOffset>()->offset,
tc);
} else if (inst->is(CheckType, AssertType)) {
// If the dest type of the instruction fits the constraint we want, we can
// stop here without constraining any further. Otherwise, continue through
// to the source.
auto changed = false;
if (inst->is(CheckType)) changed = constrainGuard(inst, tc) || changed;
auto dstType = inst->typeParam();
if (!typeFitsConstraint(dstType, tc.category)) {
changed = constrainValue(inst->src(0), tc) || changed;
}
return changed;
} else if (inst->is(StRef, StRefNT, Box, BoxPtr)) {
// If our caller cares about the inner type, propagate that through.
// Otherwise we're done.
if (tc.innerCat) {
auto src = inst->src(inst->is(StRef, StRefNT) ? 1 : 0);
tc.innerCat.reset();
return constrainValue(src, tc);
}
return false;
} else if (inst->is(LdRef, Unbox, UnboxPtr)) {
// Pass through to the source of the box, remembering that we care about
// the inner type of the box.
assert(!tc.innerCat);
tc.innerCat = tc.category;
return constrainValue(inst->src(0), tc);
} else if (inst->isPassthrough()) {
return constrainValue(inst->getPassthroughValue(), tc);
} else {
// Any instructions not special cased above produce a new value, so
// there's no guard for us to constrain.
FTRACE(2, " - value is new in this trace, bailing\n");
return false;
}
// TODO(t2598894): Should be able to do something with LdMem<T> here
}
/**
* Trace back to the guard that provided the type of val, if
* any. Constrain it so its type will not be relaxed beyond the given
* DataTypeCategory. Returns true iff one or more guard instructions
* were constrained.
*/
bool IRBuilder::constrainValue(SSATmp* const val, TypeConstraint tc) {
if (!shouldConstrainGuards()) return false;
always_assert(IMPLIES(tc.innerCat > DataTypeGeneric,
tc.category >= DataTypeCountness));
if (!val) {
ITRACE(1, "constrainValue(nullptr, {}), bailing\n", tc);
return false;
}
ITRACE(1, "constrainValue({}, {})\n", *val->inst(), tc);
Indent _i;
auto inst = val->inst();
if (inst->is(LdLoc, LdLocAddr)) {
// We've hit a LdLoc(Addr). If the source of the value is non-null and not
// a FramePtr, it's a real value that was killed by a Call. The value won't
// be live but it's ok to use it to track down the guard.
auto source = inst->extra<LocalData>()->typeSrc;
if (!source) {
// val was newly created in this trace. Nothing to constrain.
ITRACE(2, "typeSrc is null, bailing\n");
return false;
}
// If typeSrc is a FramePtr, it represents the frame the value was
// originally loaded from. Look for the guard for this local.
if (source->isA(Type::FramePtr)) {
return constrainLocal(inst->extra<LocalId>()->locId, source, tc,
"constrainValue");
}
// Otherwise, keep chasing down the source of val.
return constrainValue(source, tc);
} else if (inst->is(LdStack, LdStackAddr)) {
return constrainStack(inst->src(0), inst->extra<StackOffset>()->offset,
tc);
} else if (inst->is(AssertType)) {
// Sometimes code in HhbcTranslator asks for a value with DataTypeSpecific
// but can tolerate a less specific value. If that happens, there's nothing
// to constrain.
if (!typeFitsConstraint(val->type(), tc)) return false;
// If the immutable typeParam fits the constraint, we're done.
auto const typeParam = inst->typeParam();
if (typeFitsConstraint(typeParam, tc)) return false;
auto const newTc = relaxConstraint(tc, typeParam, inst->src(0)->type());
ITRACE(1, "tracing through {}, orig tc: {}, new tc: {}\n",
*inst, tc, newTc);
return constrainValue(inst->src(0), newTc);
} else if (inst->is(CheckType)) {
// Sometimes code in HhbcTranslator asks for a value with DataTypeSpecific
// but can tolerate a less specific value. If that happens, there's nothing
// to constrain.
if (!typeFitsConstraint(val->type(), tc)) return false;
bool changed = false;
auto const typeParam = inst->typeParam();
auto const srcType = inst->src(0)->type();
// Constrain the guard on the CheckType, but first relax the constraint
// based on what's known about srcType.
auto const guardTc = relaxConstraint(tc, srcType, typeParam);
changed = constrainGuard(inst, guardTc) || changed;
// Relax typeParam with its current constraint. This is used below to
// recursively relax the constraint on the source, if needed.
auto constraint = m_guardConstraints[inst];
constraint.category = std::max(constraint.category, guardTc.category);
constraint.innerCat = std::max(constraint.innerCat, guardTc.innerCat);
auto const knownType = refineType(relaxType(typeParam, constraint),
constraint.assertedType);
if (!typeFitsConstraint(knownType, tc)) {
auto const newTc = relaxConstraint(tc, knownType, srcType);
ITRACE(1, "tracing through {}, orig tc: {}, new tc: {}\n",
*inst, tc, newTc);
changed = constrainValue(inst->src(0), newTc) || changed;
}
return changed;
} else if (inst->is(StRef)) {
// StRef requires that src(0) is boxed so we're relying on callers to
// appropriately constrain the values they pass to it. Any innerCat in tc
// should be applied to the value being stored.
tc.category = tc.innerCat;
tc.innerCat = DataTypeGeneric;
tc.assertedType = Type::Gen;
return constrainValue(inst->src(1), tc);
} else if (inst->is(Box, BoxPtr, Unbox, UnboxPtr)) {
// All Box/Unbox opcodes are similar to StRef/LdRef in some situations and
// Mov in others (determined at runtime), so we need to constrain both
// outer and inner.
auto maxCat = std::max(tc.category, tc.innerCat);
tc.category = maxCat;
tc.innerCat = maxCat;
tc.assertedType = Type::Gen;
return constrainValue(inst->src(0), tc);
} else if (inst->is(LdRef)) {
// Constrain the inner type of the box with tc, using DataTypeCountness for
// the outer constraint to preserve the fact that it's a box.
tc.innerCat = tc.category;
tc.category = DataTypeCountness;
tc.assertedType = Type::Gen;
return constrainValue(inst->src(0), tc);
} else if (inst->isPassthrough()) {
return constrainValue(inst->getPassthroughValue(), tc);
} else {
// Any instructions not special cased above produce a new value, so
// there's no guard for us to constrain.
ITRACE(2, "value is new in this trace, bailing\n");
return false;
}
// TODO(t2598894): Should be able to do something with LdMem<T> here
}
