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Bug 1478616 - Generalize the wasm write barrier. r=bbouvier
We need to generalize the barrier to handle not just globals, but also fields in structures. To do this we pass the location of the store (ie the Cell**) to the C++ barrier machinery, not the global index. --HG-- extra : rebase_source : e036ab3500cfa838f8a7dcbfade6dcc5d5765e85
This commit is contained in:
Lars T Hansen
Родитель
5ec72ee62e
Коммит
aa46adb8f5
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@ -1891,6 +1891,7 @@ class BaseCompiler final : public BaseCompilerInterface
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ValTypeVector SigF_;
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MIRTypeVector SigP_;
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MIRTypeVector SigPI_;
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MIRTypeVector SigPL_;
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MIRTypeVector SigPII_;
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MIRTypeVector SigPIII_;
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MIRTypeVector SigPIIL_;
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@ -5614,6 +5615,97 @@ class BaseCompiler final : public BaseCompilerInterface
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masm.wasmTrap(t, bytecodeOffset());
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}
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////////////////////////////////////////////////////////////
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//
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// Object support.
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#ifdef ENABLE_WASM_GC
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// This emits a GC pre-write barrier. The pre-barrier is needed when we
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// replace a member field with a new value, and the previous field value
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// might have no other referents, and incremental GC is ongoing. The field
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// might belong to an object or be a stack slot or a register or a heap
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// allocated value.
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//
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// let obj = { field: previousValue };
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// obj.field = newValue; // previousValue must be marked with a pre-barrier.
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//
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// The `valueAddr` is the address of the location that we are about to
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// update. This function preserves that register.
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void emitPreBarrier(RegPtr valueAddr) {
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Label skipBarrier;
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MOZ_ASSERT(valueAddr == PreBarrierReg);
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ScratchPtr scratch(*this);
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// If no incremental GC has started, we don't need the barrier.
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masm.loadWasmTlsRegFromFrame(scratch);
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masm.loadPtr(Address(scratch, offsetof(TlsData, addressOfNeedsIncrementalBarrier)), scratch);
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masm.branchTest32(Assembler::Zero, Address(scratch, 0), Imm32(0x1), &skipBarrier);
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// If the previous value is null, we don't need the barrier.
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masm.loadPtr(Address(valueAddr, 0), scratch);
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masm.branchTestPtr(Assembler::Zero, scratch, scratch, &skipBarrier);
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// Call the barrier. This assumes PreBarrierReg contains the address of
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// the stored value.
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//
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// PreBarrierReg is volatile and is preserved by the barrier.
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masm.loadWasmTlsRegFromFrame(scratch);
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masm.loadPtr(Address(scratch, offsetof(TlsData, instance)), scratch);
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masm.loadPtr(Address(scratch, Instance::offsetOfPreBarrierCode()), scratch);
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masm.call(scratch);
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masm.bind(&skipBarrier);
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}
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// This emits a GC post-write barrier. This is needed to ensure that the GC
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// is aware of slots of tenured things containing references to nursery
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// values. Pass None for object when the field's owner object is known to
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// be tenured or heap-allocated.
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//
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// This frees the register `valueAddr`.
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void emitPostBarrier(const Maybe<RegPtr>& object, RegPtr otherScratch, RegPtr valueAddr, RegPtr setValue) {
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Label skipBarrier;
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// If the pointer being stored is null, no barrier.
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masm.branchTestPtr(Assembler::Zero, setValue, setValue, &skipBarrier);
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// If there is a containing object and it is in the nursery, no barrier.
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if (object)
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masm.branchPtrInNurseryChunk(Assembler::Equal, *object, otherScratch, &skipBarrier);
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// If the pointer being stored is to a tenured object, no barrier.
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masm.branchPtrInNurseryChunk(Assembler::NotEqual, setValue, otherScratch, &skipBarrier);
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// Need a barrier.
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uint32_t bytecodeOffset = iter_.lastOpcodeOffset();
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// The `valueAddr` is a raw pointer to the cell within some GC object or
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// TLS area, and we guarantee that the GC will not run while the
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// postbarrier call is active, so push a uintptr_t value.
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# ifdef JS_64BIT
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pushI64(RegI64(Register64(valueAddr)));
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emitInstanceCall(bytecodeOffset, SigPL_, ExprType::Void, SymbolicAddress::PostBarrier);
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# else
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pushI32(RegI32(valueAddr));
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emitInstanceCall(bytecodeOffset, SigPI_, ExprType::Void, SymbolicAddress::PostBarrier);
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# endif
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masm.bind(&skipBarrier);
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}
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#endif
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void emitBarrieredStore(const Maybe<RegPtr>& object, RegPtr valueAddr, RegPtr value) {
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emitPreBarrier(valueAddr); // Preserves valueAddr
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masm.storePtr(value, Address(valueAddr, 0));
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RegPtr otherScratch = needRef();
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emitPostBarrier(object, otherScratch, valueAddr, value); // Consumes valueAddr
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freeRef(otherScratch);
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}
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////////////////////////////////////////////////////////////
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//
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// Machinery for optimized conditional branches.
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@ -5721,81 +5813,6 @@ class BaseCompiler final : public BaseCompilerInterface
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masm.branch64(c, lhs, rhs, l);
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}
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#ifdef ENABLE_WASM_GC
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// The following couple of functions emit a GC pre-write barrier. This is
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// needed when we replace a member field with a new value, and the previous
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// field value might have no other referents. The field might belong to an
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// object or be a stack slot or a register or a heap allocated value.
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//
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// let obj = { field: previousValue };
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// obj.field = newValue; // previousValue must be marked with a pre-barrier.
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//
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// Implementing a pre-barrier looks like this:
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// - call `testNeedPreBarrier` with a fresh label.
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// - user code must put the address of the field we're about to clobber in
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// PreBarrierReg (to avoid explicit pushing/popping).
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// - call `emitPreBarrier`, which binds the label.
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void testNeedPreBarrier(Label* skipBarrier) {
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MOZ_ASSERT(!skipBarrier->used());
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MOZ_ASSERT(!skipBarrier->bound());
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// If no incremental GC has started, we don't need the barrier.
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ScratchPtr scratch(*this);
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masm.loadWasmTlsRegFromFrame(scratch);
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masm.loadPtr(Address(scratch, offsetof(TlsData, addressOfNeedsIncrementalBarrier)), scratch);
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masm.branchTest32(Assembler::Zero, Address(scratch, 0), Imm32(0x1), skipBarrier);
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}
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void emitPreBarrier(RegPtr valueAddr, Label* skipBarrier) {
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MOZ_ASSERT(valueAddr == PreBarrierReg);
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// If the previous value is null, we don't need the barrier.
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ScratchPtr scratch(*this);
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masm.loadPtr(Address(valueAddr, 0), scratch);
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masm.branchTestPtr(Assembler::Zero, scratch, scratch, skipBarrier);
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// Call the barrier. This assumes PreBarrierReg contains the address of
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// the stored value.
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masm.loadWasmTlsRegFromFrame(scratch);
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masm.loadPtr(Address(scratch, offsetof(TlsData, instance)), scratch);
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masm.loadPtr(Address(scratch, Instance::offsetOfPreBarrierCode()), scratch);
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masm.call(scratch);
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masm.bind(skipBarrier);
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}
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// This emits a GC post-write barrier. This is needed to ensure that the GC
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// is aware of slots of tenured things containing references to nursery
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// values. Pass None for object when the field's owner object is known to
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// be tenured or heap-allocated.
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void emitPostBarrier(const Maybe<RegPtr>& object, RegPtr setValue, PostBarrierArg arg) {
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Label skipBarrier;
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// If the set value is null, no barrier.
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masm.branchTestPtr(Assembler::Zero, setValue, setValue, &skipBarrier);
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RegPtr scratch = needRef();
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if (object) {
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// If the object value isn't tenured, no barrier.
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masm.branchPtrInNurseryChunk(Assembler::Equal, *object, scratch, &skipBarrier);
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}
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// If the set value is tenured, no barrier.
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masm.branchPtrInNurseryChunk(Assembler::NotEqual, setValue, scratch, &skipBarrier);
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freeRef(scratch);
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// Need a barrier.
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uint32_t bytecodeOffset = iter_.lastOpcodeOffset();
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pushI32(arg.rawPayload());
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emitInstanceCall(bytecodeOffset, SigPI_, ExprType::Void, SymbolicAddress::PostBarrier);
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masm.bind(&skipBarrier);
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}
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#endif
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// Emit a conditional branch that optionally and optimally cleans up the CPU
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// stack before we branch.
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//
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@ -8438,27 +8455,14 @@ BaseCompiler::emitSetGlobal()
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}
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#ifdef ENABLE_WASM_GC
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case ValType::AnyRef: {
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Label skipBarrier;
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testNeedPreBarrier(&skipBarrier);
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RegPtr valueAddr(PreBarrierReg);
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needRef(valueAddr);
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{
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ScratchI32 tmp(*this);
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masm.computeEffectiveAddress(addressOfGlobalVar(global, tmp), valueAddr);
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}
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emitPreBarrier(valueAddr, &skipBarrier);
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freeRef(valueAddr);
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RegPtr rv = popRef();
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{
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// Actual store.
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ScratchI32 tmp(*this);
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masm.storePtr(rv, addressOfGlobalVar(global, tmp));
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}
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emitPostBarrier(Nothing(), rv, PostBarrierArg::Global(id));
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emitBarrieredStore(Nothing(), valueAddr, rv); // Consumes valueAddr
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freeRef(rv);
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break;
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}
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@ -10260,6 +10264,8 @@ BaseCompiler::init()
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return false;
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if (!SigPI_.append(MIRType::Pointer) || !SigPI_.append(MIRType::Int32))
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return false;
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if (!SigPL_.append(MIRType::Pointer) || !SigPL_.append(MIRType::Int64))
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return false;
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if (!SigPII_.append(MIRType::Pointer) || !SigPII_.append(MIRType::Int32) ||
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!SigPII_.append(MIRType::Int32))
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{
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@ -678,7 +678,6 @@ AddressOf(SymbolicAddress imm, ABIFunctionType* abiType)
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#ifdef ENABLE_WASM_GC
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case SymbolicAddress::PostBarrier:
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*abiType = Args_General2;
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static_assert(sizeof(PostBarrierArg) == sizeof(uint32_t), "passed arg is a u32");
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return FuncCast(Instance::postBarrier, *abiType);
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#endif
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#if defined(JS_CODEGEN_MIPS32)
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@ -467,25 +467,10 @@ Instance::memFill(Instance* instance, uint32_t byteOffset, uint32_t value, uint3
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#ifdef ENABLE_WASM_GC
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/* static */ void
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Instance::postBarrier(Instance* instance, PostBarrierArg arg)
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Instance::postBarrier(Instance* instance, gc::Cell** location)
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{
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gc::Cell** cell = nullptr;
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switch (arg.type()) {
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case PostBarrierArg::Type::Global: {
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const GlobalDesc& global = instance->metadata().globals[arg.globalIndex()];
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MOZ_ASSERT(!global.isConstant());
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MOZ_ASSERT(global.type().isRefOrAnyRef());
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uint8_t* globalAddr = instance->globalData() + global.offset();
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if (global.isIndirect())
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globalAddr = *(uint8_t**)globalAddr;
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MOZ_ASSERT(*(JSObject**)globalAddr, "shouldn't call postbarrier if null");
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cell = (gc::Cell**) globalAddr;
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break;
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}
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}
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MOZ_ASSERT(cell);
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TlsContext.get()->runtime()->gc.storeBuffer().putCell(cell);
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MOZ_ASSERT(location);
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TlsContext.get()->runtime()->gc.storeBuffer().putCell(location);
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}
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#endif // ENABLE_WASM_GC
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@ -180,7 +180,7 @@ class Instance
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static int32_t memCopy(Instance* instance, uint32_t destByteOffset, uint32_t srcByteOffset, uint32_t len);
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static int32_t memFill(Instance* instance, uint32_t byteOffset, uint32_t value, uint32_t len);
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#ifdef ENABLE_WASM_GC
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static void postBarrier(Instance* instance, PostBarrierArg arg);
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static void postBarrier(Instance* instance, gc::Cell** location);
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#endif
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};
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@ -2375,48 +2375,6 @@ class DebugFrame
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static void alignmentStaticAsserts();
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};
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# ifdef ENABLE_WASM_GC
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// A packed format for an argument to the Instance::postBarrier function.
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class PostBarrierArg
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{
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public:
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enum class Type {
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Global = 0x0,
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Last = Global
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};
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private:
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uint32_t type_: 1;
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uint32_t payload_: 31;
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PostBarrierArg(uint32_t payload, Type type)
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: type_(uint32_t(type)),
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payload_(payload)
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{
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MOZ_ASSERT(payload < (UINT32_MAX >> 1));
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MOZ_ASSERT(uint32_t(type) <= uint32_t(Type::Last));
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}
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public:
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static PostBarrierArg Global(uint32_t globalIndex) {
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return PostBarrierArg(globalIndex, Type::Global);
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}
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Type type() const {
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MOZ_ASSERT(type_ <= uint32_t(Type::Last));
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return Type(type_);
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}
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uint32_t globalIndex() const {
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MOZ_ASSERT(type() == Type::Global);
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return payload_;
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}
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uint32_t rawPayload() const {
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return (payload_ << 1) | type_;
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}
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};
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# endif
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} // namespace wasm
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} // namespace js
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