/// It is called by AtomicExpandPass before expanding an
/// AtomicRMW/AtomicCmpXchg/AtomicStore/AtomicLoad.
/// RMW and CmpXchg set both IsStore and IsLoad to true.
- /// Backends with !getInsertFencesForAtomic() should keep a no-op here.
/// This function should either return a nullptr, or a pointer to an IR-level
/// Instruction*. Even complex fence sequences can be represented by a
/// single Instruction* through an intrinsic to be lowered later.
+ /// Backends with !getInsertFencesForAtomic() should keep a no-op here.
+ /// Backends should override this method to produce target-specific intrinsic
+ /// for their fences.
+ /// FIXME: Please note that the default implementation here in terms of
+ /// IR-level fences exists for historical/compatibility reasons and is
+ /// *unsound* ! Fences cannot, in general, be used to restore sequential
+ /// consistency. For example, consider the following example:
+ /// atomic<int> x = y = 0;
+ /// int r1, r2, r3, r4;
+ /// Thread 0:
+ /// x.store(1);
+ /// Thread 1:
+ /// y.store(1);
+ /// Thread 2:
+ /// r1 = x.load();
+ /// r2 = y.load();
+ /// Thread 3:
+ /// r3 = y.load();
+ /// r4 = x.load();
+ /// r1 = r3 = 1 and r2 = r4 = 0 is impossible as long as the accesses are all
+ /// seq_cst. But if they are lowered to monotonic accesses, no amount of
+ /// IR-level fences can prevent it.
+ /// @{
virtual Instruction* emitLeadingFence(IRBuilder<> &Builder, AtomicOrdering Ord,
bool IsStore, bool IsLoad) const {
- assert(!getInsertFencesForAtomic());
- return nullptr;
+ if (!getInsertFencesForAtomic())
+ return nullptr;
+
+ if (isAtLeastRelease(Ord) && IsStore)
+ return Builder.CreateFence(Ord);
+ else
+ return nullptr;
}
- /// Inserts in the IR a target-specific intrinsic specifying a fence.
- /// It is called by AtomicExpandPass after expanding an
- /// AtomicRMW/AtomicCmpXchg/AtomicStore/AtomicLoad.
- /// RMW and CmpXchg set both IsStore and IsLoad to true.
- /// Backends with !getInsertFencesForAtomic() should keep a no-op here.
- /// This function should either return a nullptr, or a pointer to an IR-level
- /// Instruction*. Even complex fence sequences can be represented by a
- /// single Instruction* through an intrinsic to be lowered later.
virtual Instruction* emitTrailingFence(IRBuilder<> &Builder, AtomicOrdering Ord,
bool IsStore, bool IsLoad) const {
- assert(!getInsertFencesForAtomic());
- return nullptr;
+ if (!getInsertFencesForAtomic())
+ return nullptr;
+
+ if (isAtLeastAcquire(Ord))
+ return Builder.CreateFence(Ord);
+ else
+ return nullptr;
}
+ /// @}
/// Returns true if the given (atomic) store should be expanded by the
/// IR-level AtomicExpand pass into an "atomic xchg" which ignores its input.
DAG.setRoot(StoreNode);
}
-static SDValue InsertFenceForAtomic(SDValue Chain, AtomicOrdering Order,
- SynchronizationScope Scope,
- bool Before, SDLoc dl,
- SelectionDAG &DAG,
- const TargetLowering &TLI) {
- // Fence, if necessary
- if (Before) {
- if (Order == AcquireRelease || Order == SequentiallyConsistent)
- Order = Release;
- else if (Order == Acquire || Order == Monotonic || Order == Unordered)
- return Chain;
- } else {
- if (Order == AcquireRelease)
- Order = Acquire;
- else if (Order == Release || Order == Monotonic || Order == Unordered)
- return Chain;
- }
- SDValue Ops[3];
- Ops[0] = Chain;
- Ops[1] = DAG.getConstant(Order, TLI.getPointerTy());
- Ops[2] = DAG.getConstant(Scope, TLI.getPointerTy());
- return DAG.getNode(ISD::ATOMIC_FENCE, dl, MVT::Other, Ops);
-}
-
void SelectionDAGBuilder::visitAtomicCmpXchg(const AtomicCmpXchgInst &I) {
SDLoc dl = getCurSDLoc();
AtomicOrdering SuccessOrder = I.getSuccessOrdering();
SDValue InChain = getRoot();
- const TargetLowering &TLI = DAG.getTargetLoweringInfo();
- if (TLI.getInsertFencesForAtomic())
- InChain =
- InsertFenceForAtomic(InChain, SuccessOrder, Scope, true, dl, DAG, TLI);
-
MVT MemVT = getValue(I.getCompareOperand()).getSimpleValueType();
SDVTList VTs = DAG.getVTList(MemVT, MVT::i1, MVT::Other);
SDValue L = DAG.getAtomicCmpSwap(
ISD::ATOMIC_CMP_SWAP_WITH_SUCCESS, dl, MemVT, VTs, InChain,
getValue(I.getPointerOperand()), getValue(I.getCompareOperand()),
getValue(I.getNewValOperand()), MachinePointerInfo(I.getPointerOperand()),
- 0 /* Alignment */,
- TLI.getInsertFencesForAtomic() ? Monotonic : SuccessOrder,
- TLI.getInsertFencesForAtomic() ? Monotonic : FailureOrder, Scope);
+ /*Alignment=*/ 0, SuccessOrder, FailureOrder, Scope);
SDValue OutChain = L.getValue(2);
- if (TLI.getInsertFencesForAtomic())
- OutChain = InsertFenceForAtomic(OutChain, SuccessOrder, Scope, false, dl,
- DAG, TLI);
-
setValue(&I, L);
DAG.setRoot(OutChain);
}
SDValue InChain = getRoot();
- const TargetLowering &TLI = DAG.getTargetLoweringInfo();
- if (TLI.getInsertFencesForAtomic())
- InChain = InsertFenceForAtomic(InChain, Order, Scope, true, dl, DAG, TLI);
-
- SDValue L = DAG.getAtomic(
- NT, dl, getValue(I.getValOperand()).getSimpleValueType(), InChain,
- getValue(I.getPointerOperand()), getValue(I.getValOperand()),
- I.getPointerOperand(), 0 /* Alignment */,
- TLI.getInsertFencesForAtomic() ? Monotonic : Order, Scope);
+ SDValue L =
+ DAG.getAtomic(NT, dl,
+ getValue(I.getValOperand()).getSimpleValueType(),
+ InChain,
+ getValue(I.getPointerOperand()),
+ getValue(I.getValOperand()),
+ I.getPointerOperand(),
+ /* Alignment=*/ 0, Order, Scope);
SDValue OutChain = L.getValue(1);
- if (TLI.getInsertFencesForAtomic())
- OutChain =
- InsertFenceForAtomic(OutChain, Order, Scope, false, dl, DAG, TLI);
-
setValue(&I, L);
DAG.setRoot(OutChain);
}
DAG.getEVTAlignment(VT));
InChain = TLI.prepareVolatileOrAtomicLoad(InChain, dl, DAG);
- SDValue L = DAG.getAtomic(
- ISD::ATOMIC_LOAD, dl, VT, VT, InChain, getValue(I.getPointerOperand()),
- MMO, TLI.getInsertFencesForAtomic() ? Monotonic : Order, Scope);
+ SDValue L =
+ DAG.getAtomic(ISD::ATOMIC_LOAD, dl, VT, VT, InChain,
+ getValue(I.getPointerOperand()), MMO,
+ Order, Scope);
SDValue OutChain = L.getValue(1);
- if (TLI.getInsertFencesForAtomic())
- OutChain = InsertFenceForAtomic(OutChain, Order, Scope, false, dl,
- DAG, TLI);
-
setValue(&I, L);
DAG.setRoot(OutChain);
}
if (I.getAlignment() < VT.getSizeInBits() / 8)
report_fatal_error("Cannot generate unaligned atomic store");
- if (TLI.getInsertFencesForAtomic())
- InChain = InsertFenceForAtomic(InChain, Order, Scope, true, dl, DAG, TLI);
-
- SDValue OutChain = DAG.getAtomic(
- ISD::ATOMIC_STORE, dl, VT, InChain, getValue(I.getPointerOperand()),
- getValue(I.getValueOperand()), I.getPointerOperand(), I.getAlignment(),
- TLI.getInsertFencesForAtomic() ? Monotonic : Order, Scope);
-
- if (TLI.getInsertFencesForAtomic())
- OutChain =
- InsertFenceForAtomic(OutChain, Order, Scope, false, dl, DAG, TLI);
+ SDValue OutChain =
+ DAG.getAtomic(ISD::ATOMIC_STORE, dl, VT,
+ InChain,
+ getValue(I.getPointerOperand()),
+ getValue(I.getValueOperand()),
+ I.getPointerOperand(), I.getAlignment(),
+ Order, Scope);
DAG.setRoot(OutChain);
}
projects / oota-llvm.git / commitdiff