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Bug 1814519 - wasm: Don't emit pre-write barrier for initialization of structs/arrays. r=jseward

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Arrays/structs are initialized to be completely null. The pre-write barrier will
always be dead code for them.

Differential Revision: https://phabricator.services.mozilla.com/D168618
This commit is contained in:
Ryan Hunt 2023-02-17 01:15:58 +00:00
parent 528f75b536
commit 34a2ac98fd
2 changed files with 42 additions and 20 deletions
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17
js/src/wasm/WasmBCClass.h
View File

@ -150,6 +150,14 @@ struct FunctionCall {
size_t stackArgAreaSize;
};
enum class PreBarrierKind {
// No pre-write barrier is required because the previous value is undefined.
None,
// Perform a pre-write barrier to mark the previous value if an incremental
// GC is underway.
Normal,
};
enum class PostBarrierKind {
// Remove an existing store buffer entry if the new value does not require
// one. This is required to preserve invariants with HeapPtr when used for
@ -1306,7 +1314,8 @@ struct BaseCompiler final {
// Preserves `object` and `value`. Consumes `valueAddr`.
[[nodiscard]] bool emitBarrieredStore(const Maybe<RegRef>& object,
RegPtr valueAddr, RegRef value,
PostBarrierKind kind);
PreBarrierKind preBarrierKind,
PostBarrierKind postBarrierKind);
// Emits a store of nullptr to a JS object pointer at the address valueAddr.
// Preserves `valueAddr`.
@ -1683,10 +1692,12 @@ struct BaseCompiler final {
template <typename NullCheckPolicy>
[[nodiscard]] bool emitGcStructSet(RegRef object, RegPtr areaBase,
uint32_t areaOffset, FieldType fieldType,
AnyReg value);
AnyReg value,
PreBarrierKind preBarrierKind);
[[nodiscard]] bool emitGcArraySet(RegRef object, RegPtr data, RegI32 index,
const ArrayType& array, AnyReg value);
const ArrayType& array, AnyReg value,
PreBarrierKind preBarrierKind);
#endif // ENABLE_WASM_GC
#ifdef ENABLE_WASM_SIMD

45
js/src/wasm/WasmBaselineCompile.cpp
View File

@ -4465,6 +4465,7 @@ bool BaseCompiler::emitThrow() {
pushPtr(data);
// emitBarrieredStore preserves exn, rv
if (!emitBarrieredStore(Some(exn), valueAddr, rv,
PreBarrierKind::Normal,
PostBarrierKind::Imprecise)) {
return false;
}
@ -5380,7 +5381,7 @@ bool BaseCompiler::emitSetGlobal() {
}
RegRef rv = popRef();
// emitBarrieredStore preserves rv
if (!emitBarrieredStore(Nothing(), valueAddr, rv,
if (!emitBarrieredStore(Nothing(), valueAddr, rv, PreBarrierKind::Normal,
PostBarrierKind::Imprecise)) {
return false;
}
@ -6194,7 +6195,7 @@ bool BaseCompiler::emitTableSetAnyRef(uint32_t tableIndex) {
value = popRef();
#endif
if (!emitBarrieredStore(Nothing(), valueAddr, value,
if (!emitBarrieredStore(Nothing(), valueAddr, value, PreBarrierKind::Normal,
PostBarrierKind::Precise)) {
return false;
}
@ -6310,18 +6311,21 @@ bool BaseCompiler::emitPostBarrierPrecise(const Maybe<RegRef>& object,
bool BaseCompiler::emitBarrieredStore(const Maybe<RegRef>& object,
RegPtr valueAddr, RegRef value,
PostBarrierKind kind) {
PreBarrierKind preBarrierKind,
PostBarrierKind postBarrierKind) {
// TODO/AnyRef-boxing: With boxed immediates and strings, the write
// barrier is going to have to be more complicated.
ASSERT_ANYREF_IS_JSOBJECT;
// The pre-barrier preserves all allocated registers.
emitPreBarrier(valueAddr);
if (preBarrierKind == PreBarrierKind::Normal) {
emitPreBarrier(valueAddr);
}
// The precise post-barrier requires the previous value stored in the field,
// in order to know if the previous store buffer entry needs to be removed.
RegRef prevValue;
if (kind == PostBarrierKind::Precise) {
if (postBarrierKind == PostBarrierKind::Precise) {
prevValue = needRef();
masm.loadPtr(Address(valueAddr, 0), prevValue);
}
@ -6330,7 +6334,7 @@ bool BaseCompiler::emitBarrieredStore(const Maybe<RegRef>& object,
masm.storePtr(value, Address(valueAddr, 0));
// The post-barrier preserves object and value.
if (kind == PostBarrierKind::Precise) {
if (postBarrierKind == PostBarrierKind::Precise) {
return emitPostBarrierPrecise(object, valueAddr, prevValue, value);
}
return emitPostBarrierImprecise(object, valueAddr, value);
@ -6580,7 +6584,8 @@ void BaseCompiler::emitGcSetScalar(const T& dst, FieldType type, AnyReg value) {
template <typename NullCheckPolicy>
bool BaseCompiler::emitGcStructSet(RegRef object, RegPtr areaBase,
uint32_t areaOffset, FieldType fieldType,
AnyReg value) {
AnyReg value,
PreBarrierKind preBarrierKind) {
// Easy path if the field is a scalar
if (!fieldType.isRefRepr()) {
emitGcSetScalar<Address, NullCheckPolicy>(Address(areaBase, areaOffset),
@ -6598,7 +6603,7 @@ bool BaseCompiler::emitGcStructSet(RegRef object, RegPtr areaBase,
NullCheckPolicy::emitNullCheck(this, object);
// emitBarrieredStore preserves object and value
if (!emitBarrieredStore(Some(object), valueAddr, value.ref(),
if (!emitBarrieredStore(Some(object), valueAddr, value.ref(), preBarrierKind,
PostBarrierKind::Imprecise)) {
return false;
}
@ -6608,7 +6613,8 @@ bool BaseCompiler::emitGcStructSet(RegRef object, RegPtr areaBase,
}
bool BaseCompiler::emitGcArraySet(RegRef object, RegPtr data, RegI32 index,
const ArrayType& arrayType, AnyReg value) {
const ArrayType& arrayType, AnyReg value,
PreBarrierKind preBarrierKind) {
// Try to use a base index store instruction if the field type fits in a
// shift immediate. If not we shift the index manually and then unshift
// it after the store. We don't use an extra register for this because we
@ -6647,7 +6653,7 @@ bool BaseCompiler::emitGcArraySet(RegRef object, RegPtr data, RegI32 index,
pushI32(index);
// emitBarrieredStore preserves object and value
if (!emitBarrieredStore(Some(object), valueAddr, value.ref(),
if (!emitBarrieredStore(Some(object), valueAddr, value.ref(), preBarrierKind,
PostBarrierKind::Imprecise)) {
return false;
}
@ -6736,7 +6742,8 @@ bool BaseCompiler::emitStructNew() {
// Consumes value and outline data, object is preserved by this call.
if (!emitGcStructSet<NoNullCheck>(object, outlineBase, areaOffset,
fieldType, value)) {
fieldType, value,
PreBarrierKind::None)) {
return false;
}
} else {
@ -6744,7 +6751,7 @@ bool BaseCompiler::emitStructNew() {
if (!emitGcStructSet<NoNullCheck>(
object, RegPtr(object),
WasmStructObject::offsetOfInlineData() + areaOffset, fieldType,
value)) {
value, PreBarrierKind::None)) {
return false;
}
}
@ -6862,7 +6869,8 @@ bool BaseCompiler::emitStructSet() {
masm.loadPtr(Address(object, WasmStructObject::offsetOfOutlineData()),
outlineBase);
if (!emitGcStructSet<NoNullCheck>(object, outlineBase, areaOffset,
fieldType, value)) {
fieldType, value,
PreBarrierKind::Normal)) {
return false;
}
} else {
@ -6870,7 +6878,7 @@ bool BaseCompiler::emitStructSet() {
if (!emitGcStructSet<SignalNullCheck>(
object, RegPtr(object),
WasmStructObject::offsetOfInlineData() + areaOffset, fieldType,
value)) {
value, PreBarrierKind::Normal)) {
return false;
}
}
@ -6935,7 +6943,8 @@ bool BaseCompiler::emitArrayNew() {
masm.sub32(Imm32(1), numElements);
// Assign value to array[numElements]. All registers are preserved
if (!emitGcArraySet(rp, rdata, numElements, arrayType, value)) {
if (!emitGcArraySet(rp, rdata, numElements, arrayType, value,
PreBarrierKind::None)) {
return false;
}
@ -7013,7 +7022,8 @@ bool BaseCompiler::emitArrayNewFixed() {
if (avoidPreBarrierReg) {
freePtr(RegPtr(PreBarrierReg));
}
if (!emitGcArraySet(rp, rdata, index, arrayType, value)) {
if (!emitGcArraySet(rp, rdata, index, arrayType, value,
PreBarrierKind::None)) {
return false;
}
freeI32(index);
@ -7169,7 +7179,8 @@ bool BaseCompiler::emitArraySet() {
// All registers are preserved. This isn't strictly necessary, as we'll just
// be freeing them all after this is done. But this is needed for repeated
// assignments used in array.new/new_default.
if (!emitGcArraySet(rp, rdata, index, arrayType, value)) {
if (!emitGcArraySet(rp, rdata, index, arrayType, value,
PreBarrierKind::Normal)) {
return false;
}