[SDAG] Update generic code to conservatively check for isAtomic in addition to isVolatile

[reames]

Summary

See D66309 for context.

This is the first sweep of generic code to add isAtomic bailouts where appropriate. The intention here is to have the switch from AtomicSDNode to LoadSDNode/StoreSDNode be close to NFC; that is, I'm not looking to allow additional optimizations at this time. That will come later.

(Note: This is currently based on ToT without D66309. That's why there are no test diffs with the experimental flag visible. It could be added either before or after that change.)

[reames]

update all todos with an easily grepable tag for ease of future work

[reames]

Waiting behind D66322 since that's where discussion has happened. Once that's in, will rebase with the same changes here.

[reames]

Porting a comment from craig.topper over on D66322:
"Will you also be updating nonvolatile_load/nonvolatile_store in include/llvm/Target/TargetSelectionDAG.td. We use those in several places where we change the size of a load."

Needs addressed in rebase.

[reames]

Rebase to include isSimple usage, and test updates.

Still need to include the nonvolatile_load/nonvolatile_store cases. Need access to a larger build machine for that one. :)

[reames]

Add the nonvolatile_load/store cases. I'll rename them in a separate commit so as not to clutter the diff on this one.

With that, we're catching *most* of the atomic vs non-atomic differences. Skimming the remaining test diffs, I clearly need to adjust my test lines to hide O3 vs experimental O3 differences. There do appear to be a few remaining cases that are being miscompiled, mostly around widenable store idioms. Need to track that down in a future patch.

[reames]

ping

[arsenm]

LGTM with nits

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

13807–13808

Capitalize comment

16084

Ditto

16095

Ditto

16226

Ditto

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

bool DAGCombiner::isAndLoadExtLoad(ConstantSDNode *AndC, LoadSDNode *LoadN,
   if (ExtVT == LoadedVT &&
       (!LegalOperations ||
        TLI.isLoadExtLegal(ISD::ZEXTLOAD, LoadResultTy, ExtVT))) {
     // ZEXTLOAD will match without needing to change the size of the value being
     // loaded.
     return true;
   }
 
-  // Do not change the width of a volatile load.
-  if (LoadN->isVolatile())
+  // Do not change the width of a volatile or atomic loads.
+  if (LoadN->isVolatile() || LoadN->isAtomic())
     return false;
 
   // Do not generate loads of non-round integer types since these can
   // be expensive (and would be wrong if the type is not byte sized).
   if (!LoadedVT.bitsGT(ExtVT) || !ExtVT.isRound())
     return false;
 
   if (LegalOperations &&
bool DAGCombiner::isLegalNarrowLdSt(LSBaseSDNode *LDST,
   if (ShAmt % 8)
     return false;
 
   // Do not generate loads of non-round integer types since these can
   // be expensive (and would be wrong if the type is not byte sized).
   if (!MemVT.isRound())
     return false;
 
-  // Don't change the width of a volatile load.
-  if (LDST->isVolatile())
+  // Don't change the width of a volatile or atomic loads.
+  if (LDST->isVolatile() || LDST->isAtomic())
     return false;
 
   // Verify that we are actually reducing a load width here.
   if (LDST->getMemoryVT().getSizeInBits() < MemVT.getSizeInBits())
     return false;
 
   // Ensure that this isn't going to produce an unsupported unaligned access.
   if (ShAmt &&
if (ISD::isUNINDEXEDLoad(N0.getNode()) &&
     LoadSDNode *LN0 = cast<LoadSDNode>(N0);
     EVT MemVT = LN0->getMemoryVT();
     // If we zero all the possible extended bits, then we can turn this into
     // a zextload if we are running before legalize or the operation is legal.
     unsigned ExtBitSize = N1.getScalarValueSizeInBits();
     unsigned MemBitSize = MemVT.getScalarSizeInBits();
     APInt ExtBits = APInt::getHighBitsSet(ExtBitSize, ExtBitSize - MemBitSize);
     if (DAG.MaskedValueIsZero(N1, ExtBits) &&
-        ((!LegalOperations && !LN0->isVolatile()) ||
+        ((!LegalOperations && !LN0->isVolatile() && !LN0->isAtomic()) ||
          TLI.isLoadExtLegal(ISD::ZEXTLOAD, VT, MemVT))) {
       SDValue ExtLoad =
           DAG.getExtLoad(ISD::ZEXTLOAD, SDLoc(N0), VT, LN0->getChain(),
                          LN0->getBasePtr(), MemVT, LN0->getMemOperand());
       AddToWorklist(N);
       CombineTo(N0.getNode(), ExtLoad, ExtLoad.getValue(1));
       return SDValue(N, 0); // Return N so it doesn't get rechecked!
     }
if (Index >= NarrowByteWidth)
                  : None;
     return calculateByteProvider(NarrowOp, Index, Depth + 1);
   }
   case ISD::BSWAP:
     return calculateByteProvider(Op->getOperand(0), ByteWidth - Index - 1,
                                  Depth + 1);
   case ISD::LOAD: {
     auto L = cast<LoadSDNode>(Op.getNode());
-    if (L->isVolatile() || L->isIndexed())
+    if (L->isVolatile() || L->isAtomic() || L->isIndexed())
       return None;
 
     unsigned NarrowBitWidth = L->getMemoryVT().getSizeInBits();
     if (NarrowBitWidth % 8 != 0)
       return None;
     uint64_t NarrowByteWidth = NarrowBitWidth / 8;
 
     if (Index >= NarrowByteWidth)

 /// =>
 ///  *((i32)p) = BSWAP(val);
 SDValue DAGCombiner::MatchStoreCombine(StoreSDNode *N) {
   // Collect all the stores in the chain.
   SDValue Chain;
   SmallVector<StoreSDNode *, 8> Stores;
   for (StoreSDNode *Store = N; Store; Store = dyn_cast<StoreSDNode>(Chain)) {
     if (Store->getMemoryVT() != MVT::i8 ||
-        Store->isVolatile() || Store->isIndexed())
+        Store->isVolatile() || Store->isAtomic() || Store->isIndexed())
       return SDValue();
     Stores.push_back(Store);
     Chain = Store->getChain();
   }
   // Handle the simple type only.
   unsigned Width = Stores.size();
   EVT VT = EVT::getIntegerVT(
     *DAG.getContext(), Width * N->getMemoryVT().getSizeInBits());
SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
   // base address. Collect bytes offsets from Base address in ByteOffsets.
   SmallVector<int64_t, 4> ByteOffsets(ByteWidth);
   for (unsigned i = 0; i < ByteWidth; i++) {
     auto P = calculateByteProvider(SDValue(N, 0), i, 0, /*Root=*/true);
     if (!P || !P->isMemory()) // All the bytes must be loaded from memory
       return SDValue();
 
     LoadSDNode *L = P->Load;
-    assert(L->hasNUsesOfValue(1, 0) && !L->isVolatile() && !L->isIndexed() &&
+    assert(L->hasNUsesOfValue(1, 0) && !L->isVolatile() && !L->isAtomic() &&
+           !L->isIndexed() &&
            "Must be enforced by calculateByteProvider");
     assert(L->getOffset().isUndef() && "Unindexed load must have undef offset");
 
     // All loads must share the same chain
     SDValue LChain = L->getChain();
     if (!Chain)
       Chain = LChain;
     else if (Chain != LChain)
SDValue DAGCombiner::CombineExtLoad(SDNode *N) {
   // This combine is controlled by TargetLowering::isVectorLoadExtDesirable.
   //
   if (N0->getOpcode() != ISD::LOAD)
     return SDValue();
 
   LoadSDNode *LN0 = cast<LoadSDNode>(N0);
 
   if (!ISD::isNON_EXTLoad(LN0) || !ISD::isUNINDEXEDLoad(LN0) ||
-      !N0.hasOneUse() || LN0->isVolatile() || !DstVT.isVector() ||
-      !DstVT.isPow2VectorType() || !TLI.isVectorLoadExtDesirable(SDValue(N, 0)))
+      !N0.hasOneUse() || LN0->isVolatile() || LN0->isAtomic() ||
+      !DstVT.isVector() || !DstVT.isPow2VectorType() ||
+      !TLI.isVectorLoadExtDesirable(SDValue(N, 0)))
     return SDValue();
 
   SmallVector<SDNode *, 4> SetCCs;
   if (!ExtendUsesToFormExtLoad(DstVT, N, N0, N->getOpcode(), SetCCs, TLI))
     return SDValue();
 
   ISD::LoadExtType ExtType =
       N->getOpcode() == ISD::SIGN_EXTEND ? ISD::SEXTLOAD : ISD::ZEXTLOAD;
static SDValue tryToFoldExtOfExtload(SelectionDAG &DAG, DAGCombiner &Combiner,
   bool isAExtLoad = (ExtLoadType == ISD::SEXTLOAD) ? ISD::isSEXTLoad(N0Node)
                                                    : ISD::isZEXTLoad(N0Node);
   if ((!isAExtLoad && !ISD::isEXTLoad(N0Node)) ||
       !ISD::isUNINDEXEDLoad(N0Node) || !N0.hasOneUse())
     return SDValue();
 
   LoadSDNode *LN0 = cast<LoadSDNode>(N0);
   EVT MemVT = LN0->getMemoryVT();
-  if ((LegalOperations || LN0->isVolatile() || VT.isVector()) &&
+  if ((LegalOperations || LN0->isVolatile() || LN0->isAtomic() ||
+       VT.isVector()) &&
       !TLI.isLoadExtLegal(ExtLoadType, VT, MemVT))
     return SDValue();
 
   SDValue ExtLoad =
       DAG.getExtLoad(ExtLoadType, SDLoc(LN0), VT, LN0->getChain(),
                      LN0->getBasePtr(), MemVT, LN0->getMemOperand());
   Combiner.CombineTo(N, ExtLoad);
   DAG.ReplaceAllUsesOfValueWith(SDValue(LN0, 1), ExtLoad.getValue(1));
   if (LN0->use_empty())
     Combiner.recursivelyDeleteUnusedNodes(LN0);
   return SDValue(N, 0); // Return N so it doesn't get rechecked!
 }
 
 // fold ([s|z]ext (load x)) -> ([s|z]ext (truncate ([s|z]extload x)))
 // Only generate vector extloads when 1) they're legal, and 2) they are
 // deemed desirable by the target.
 static SDValue tryToFoldExtOfLoad(SelectionDAG &DAG, DAGCombiner &Combiner,
                                   const TargetLowering &TLI, EVT VT,
                                   bool LegalOperations, SDNode *N, SDValue N0,
                                   ISD::LoadExtType ExtLoadType,
                                   ISD::NodeType ExtOpc) {
   if (!ISD::isNON_EXTLoad(N0.getNode()) ||
       !ISD::isUNINDEXEDLoad(N0.getNode()) ||
       ((LegalOperations || VT.isVector() ||
-        cast<LoadSDNode>(N0)->isVolatile()) &&
+        cast<LoadSDNode>(N0)->isVolatile() ||
+        cast<LoadSDNode>(N0)->isAtomic()) &&
        !TLI.isLoadExtLegal(ExtLoadType, VT, N0.getValueType())))
     return {};
 
   bool DoXform = true;
   SmallVector<SDNode *, 4> SetCCs;
   if (!N0.hasOneUse())
     DoXform = ExtendUsesToFormExtLoad(VT, N, N0, ExtOpc, SetCCs, TLI);
   if (VT.isVector())
SDValue DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
   // fold (sext_inreg (extload x)) -> (sextload x)
   // If sextload is not supported by target, we can only do the combine when
   // load has one use. Doing otherwise can block folding the extload with other
   // extends that the target does support.
   if (ISD::isEXTLoad(N0.getNode()) &&
       ISD::isUNINDEXEDLoad(N0.getNode()) &&
       EVT == cast<LoadSDNode>(N0)->getMemoryVT() &&
       ((!LegalOperations && !cast<LoadSDNode>(N0)->isVolatile() &&
+        !cast<LoadSDNode>(N0)->isAtomic() &&
         N0.hasOneUse()) ||
        TLI.isLoadExtLegal(ISD::SEXTLOAD, VT, EVT))) {
     LoadSDNode *LN0 = cast<LoadSDNode>(N0);
     SDValue ExtLoad = DAG.getExtLoad(ISD::SEXTLOAD, SDLoc(N), VT,
                                      LN0->getChain(),
                                      LN0->getBasePtr(), EVT,
                                      LN0->getMemOperand());
     CombineTo(N, ExtLoad);
     CombineTo(N0.getNode(), ExtLoad, ExtLoad.getValue(1));
     AddToWorklist(ExtLoad.getNode());
     return SDValue(N, 0);   // Return N so it doesn't get rechecked!
   }
   // fold (sext_inreg (zextload x)) -> (sextload x) iff load has one use
   if (ISD::isZEXTLoad(N0.getNode()) && ISD::isUNINDEXEDLoad(N0.getNode()) &&
       N0.hasOneUse() &&
       EVT == cast<LoadSDNode>(N0)->getMemoryVT() &&
-      ((!LegalOperations && !cast<LoadSDNode>(N0)->isVolatile()) ||
+      ((!LegalOperations && !cast<LoadSDNode>(N0)->isVolatile() &&
+        !cast<LoadSDNode>(N0)->isAtomic()) ||
        TLI.isLoadExtLegal(ISD::SEXTLOAD, VT, EVT))) {
     LoadSDNode *LN0 = cast<LoadSDNode>(N0);
     SDValue ExtLoad = DAG.getExtLoad(ISD::SEXTLOAD, SDLoc(N), VT,
                                      LN0->getChain(),
                                      LN0->getBasePtr(), EVT,
                                      LN0->getMemOperand());
     CombineTo(N, ExtLoad);
     CombineTo(N0.getNode(), ExtLoad, ExtLoad.getValue(1));
SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
   if (!LegalTypes || TLI.isTypeDesirableForOp(N0.getOpcode(), VT)) {
     if (SDValue Reduced = ReduceLoadWidth(N))
       return Reduced;
 
     // Handle the case where the load remains an extending load even
     // after truncation.
     if (N0.hasOneUse() && ISD::isUNINDEXEDLoad(N0.getNode())) {
       LoadSDNode *LN0 = cast<LoadSDNode>(N0);
-      if (!LN0->isVolatile() &&
+      if (!LN0->isVolatile() && !LN0->isAtomic() &&
           LN0->getMemoryVT().getStoreSizeInBits() < VT.getSizeInBits()) {
         SDValue NewLoad = DAG.getExtLoad(LN0->getExtensionType(), SDLoc(LN0),
                                          VT, LN0->getChain(), LN0->getBasePtr(),
                                          LN0->getMemoryVT(),
                                          LN0->getMemOperand());
         DAG.ReplaceAllUsesOfValueWith(N0.getValue(1), NewLoad.getValue(1));
         return NewLoad;
       }
if (ISD::isNormalLoad(N0.getNode()) && N0.hasOneUse() &&
       // Do not remove the cast if the types differ in endian layout.
       TLI.hasBigEndianPartOrdering(N0.getValueType(), DAG.getDataLayout()) ==
           TLI.hasBigEndianPartOrdering(VT, DAG.getDataLayout()) &&
       // If the load is volatile, we only want to change the load type if the
       // resulting load is legal. Otherwise we might increase the number of
       // memory accesses. We don't care if the original type was legal or not
       // as we assume software couldn't rely on the number of accesses of an
       // illegal type.
-      ((!LegalOperations && !cast<LoadSDNode>(N0)->isVolatile()) ||
+      ((!LegalOperations && !cast<LoadSDNode>(N0)->isVolatile() &&
+        !cast<LoadSDNode>(N0)->isAtomic()) ||
        TLI.isOperationLegal(ISD::LOAD, VT))) {
     LoadSDNode *LN0 = cast<LoadSDNode>(N0);
 
     if (TLI.isLoadBitCastBeneficial(N0.getValueType(), VT, DAG,
                                     *LN0->getMemOperand())) {
       SDValue Load =
           DAG.getLoad(VT, SDLoc(N), LN0->getChain(), LN0->getBasePtr(),
                       LN0->getPointerInfo(), LN0->getAlignment(),
case ISD::ZEXTLOAD:
       Val = DAG.getNode(ISD::ZERO_EXTEND, SDLoc(LD), LDType, Val);
       return true;
     }
   }
   return false;
 }
 
 SDValue DAGCombiner::ForwardStoreValueToDirectLoad(LoadSDNode *LD) {
-  if (OptLevel == CodeGenOpt::None || LD->isVolatile())
+  if (OptLevel == CodeGenOpt::None || LD->isVolatile() || LD->isAtomic())
     return SDValue();
   SDValue Chain = LD->getOperand(0);
   StoreSDNode *ST = dyn_cast<StoreSDNode>(Chain.getNode());
-  if (!ST || ST->isVolatile())
+  // TODO: relax this restriction for unordered atomics
+  if (!ST || ST->isVolatile() || ST->isAtomic())
     return SDValue();
 
   EVT LDType = LD->getValueType(0);
   EVT LDMemType = LD->getMemoryVT();
   EVT STMemType = ST->getMemoryVT();
   EVT STType = ST->getValue().getValueType();
 
   BaseIndexOffset BasePtrLD = BaseIndexOffset::match(LD, DAG);

 SDValue DAGCombiner::visitLOAD(SDNode *N) {
   LoadSDNode *LD  = cast<LoadSDNode>(N);
   SDValue Chain = LD->getChain();
   SDValue Ptr   = LD->getBasePtr();
 
   // If load is not volatile and there are no uses of the loaded value (and
   // the updated indexed value in case of indexed loads), change uses of the
   // chain value into uses of the chain input (i.e. delete the dead load).
-  if (!LD->isVolatile()) {
+  // TODO: Allow this for unordered atomics
+  if (!LD->isVolatile() && !LD->isAtomic()) {
     if (N->getValueType(1) == MVT::Other) {
       // Unindexed loads.
       if (!N->hasAnyUseOfValue(0)) {
         // It's not safe to use the two value CombineTo variant here. e.g.
         // v1, chain2 = load chain1, loc
         // v2, chain3 = load chain2, loc
         // v3         = add v2, c
         // Now we replace use of chain2 with chain1.  This makes the second load

 /// This sort of thing is introduced by SROA.
 /// This slicing takes care not to insert overlapping loads.
 /// \pre LI is a simple load (i.e., not an atomic or volatile load).
 bool DAGCombiner::SliceUpLoad(SDNode *N) {
   if (Level < AfterLegalizeDAG)
     return false;
 
   LoadSDNode *LD = cast<LoadSDNode>(N);
-  if (LD->isVolatile() || !ISD::isNormalLoad(LD) ||
+  if (LD->isVolatile() || LD->isAtomic() || !ISD::isNormalLoad(LD) ||
       !LD->getValueType(0).isInteger())
     return false;
 
   // Keep track of already used bits to detect overlapping values.
   // In that case, we will just abort the transformation.
   APInt UsedBits(LD->getValueSizeInBits(0), 0);
 
   SmallVector<LoadedSlice, 4> LoadedSlices;

 }
 
 /// Look for sequence of load / op / store where op is one of 'or', 'xor', and
 /// 'and' of immediates. If 'op' is only touching some of the loaded bits, try
 /// narrowing the load and store if it would end up being a win for performance
 /// or code size.
 SDValue DAGCombiner::ReduceLoadOpStoreWidth(SDNode *N) {
   StoreSDNode *ST  = cast<StoreSDNode>(N);
-  if (ST->isVolatile())
+  if (ST->isVolatile() || ST->isAtomic())
     return SDValue();
 
   SDValue Chain = ST->getChain();
   SDValue Value = ST->getValue();
   SDValue Ptr   = ST->getBasePtr();
   EVT VT = Value.getValueType();
 
   if (ST->isTruncatingStore() || VT.isVector() || !Value.hasOneUse())
if (IsLoadSrc) {
     LBasePtr = BaseIndexOffset::match(Ld, DAG);
     LoadVT = Ld->getMemoryVT();
     // Load and store should be the same type.
     if (MemVT != LoadVT)
       return;
     // Loads must only have one use.
     if (!Ld->hasNUsesOfValue(1, 0))
       return;
-    // The memory operands must not be volatile/indexed.
-    if (Ld->isVolatile() || Ld->isIndexed())
+    // The memory operands must not be volatile/indexed/atomic.
+    if (Ld->isVolatile() || Ld->isAtomic() || Ld->isIndexed())
       return;
   }
   auto CandidateMatch = [&](StoreSDNode *Other, BaseIndexOffset &Ptr,
                             int64_t &Offset) -> bool {
-    // The memory operands must not be volatile/indexed.
-    if (Other->isVolatile() || Other->isIndexed())
+    // The memory operands must not be volatile/indexed/atomic.
+    if (Other->isVolatile() || Other->isAtomic() ||  Other->isIndexed())
       return false;
     // Don't mix temporal stores with non-temporal stores.
     if (St->isNonTemporal() != Other->isNonTemporal())
       return false;
     SDValue OtherBC = peekThroughBitcasts(Other->getValue());
     // Allow merging constants of different types as integers.
     bool NoTypeMatch = (MemVT.isInteger()) ? !MemVT.bitsEq(Other->getMemoryVT())
                                            : Other->getMemoryVT() != MemVT;
     if (IsLoadSrc) {
       if (NoTypeMatch)
         return false;
       // The Load's Base Ptr must also match
       if (LoadSDNode *OtherLd = dyn_cast<LoadSDNode>(OtherBC)) {
         BaseIndexOffset LPtr = BaseIndexOffset::match(OtherLd, DAG);
         if (LoadVT != OtherLd->getMemoryVT())
           return false;
         // Loads must only have one use.
         if (!OtherLd->hasNUsesOfValue(1, 0))
           return false;
-        // The memory operands must not be volatile/indexed.
-        if (OtherLd->isVolatile() || OtherLd->isIndexed())
+        // The memory operands must not be volatile/indexed/atomic.
+        if (OtherLd->isVolatile() || OtherLd->isAtomic() ||
+            OtherLd->isIndexed())
           return false;
         // Don't mix temporal loads with non-temporal loads.
         if (cast<LoadSDNode>(Val)->isNonTemporal() != OtherLd->isNonTemporal())
           return false;
         if (!(LBasePtr.equalBaseIndex(LPtr, DAG)))
           return false;
       } else
         return false;
SDValue DAGCombiner::replaceStoreOfFPConstant(StoreSDNode *ST) {
   default:
     llvm_unreachable("Unknown FP type");
   case MVT::f16:    // We don't do this for these yet.
   case MVT::f80:
   case MVT::f128:
   case MVT::ppcf128:
     return SDValue();
   case MVT::f32:
-    if ((isTypeLegal(MVT::i32) && !LegalOperations && !ST->isVolatile()) ||
+    if ((isTypeLegal(MVT::i32) && !LegalOperations && !ST->isVolatile() &&
+         !ST->isAtomic()) ||
         TLI.isOperationLegalOrCustom(ISD::STORE, MVT::i32)) {
       ;
       Tmp = DAG.getConstant((uint32_t)CFP->getValueAPF().
                             bitcastToAPInt().getZExtValue(), SDLoc(CFP),
                             MVT::i32);
       return DAG.getStore(Chain, DL, Tmp, Ptr, ST->getMemOperand());
     }
 
     return SDValue();
   case MVT::f64:
     if ((TLI.isTypeLegal(MVT::i64) && !LegalOperations &&
-         !ST->isVolatile()) ||
+         !ST->isVolatile() && !ST->isAtomic()) ||
         TLI.isOperationLegalOrCustom(ISD::STORE, MVT::i64)) {
       ;
       Tmp = DAG.getConstant(CFP->getValueAPF().bitcastToAPInt().
                             getZExtValue(), SDLoc(CFP), MVT::i64);
       return DAG.getStore(Chain, DL, Tmp,
                           Ptr, ST->getMemOperand());
     }
 
-    if (!ST->isVolatile() &&
+    if (!ST->isVolatile() && !ST->isAtomic() &&
         TLI.isOperationLegalOrCustom(ISD::STORE, MVT::i32)) {
       // Many FP stores are not made apparent until after legalize, e.g. for
       // argument passing.  Since this is so common, custom legalize the
       // 64-bit integer store into two 32-bit stores.
       uint64_t Val = CFP->getValueAPF().bitcastToAPInt().getZExtValue();
       SDValue Lo = DAG.getConstant(Val & 0xFFFFFFFF, SDLoc(CFP), MVT::i32);
       SDValue Hi = DAG.getConstant(Val >> 32, SDLoc(CFP), MVT::i32);
       if (DAG.getDataLayout().isBigEndian())
SDValue DAGCombiner::visitSTORE(SDNode *N) {
   if (Value.getOpcode() == ISD::BITCAST && !ST->isTruncatingStore() &&
       ST->isUnindexed()) {
     EVT SVT = Value.getOperand(0).getValueType();
     // If the store is volatile, we only want to change the store type if the
     // resulting store is legal. Otherwise we might increase the number of
     // memory accesses. We don't care if the original type was legal or not
     // as we assume software couldn't rely on the number of accesses of an
     // illegal type.
-    if (((!LegalOperations && !ST->isVolatile()) ||
+    if (((!LegalOperations && !ST->isVolatile() && !ST->isAtomic()) ||
          TLI.isOperationLegal(ISD::STORE, SVT)) &&
         TLI.isStoreBitCastBeneficial(Value.getValueType(), SVT,
                                      DAG, *ST->getMemOperand())) {
       return DAG.getStore(Chain, SDLoc(N), Value.getOperand(0), Ptr,
                           ST->getPointerInfo(), ST->getAlignment(),
                           ST->getMemOperand()->getFlags(), ST->getAAInfo());
     }
   }
if (SimplifyDemandedBits(Value, TruncDemandedBits)) {
       if (N->getOpcode() != ISD::DELETED_NODE)
         AddToWorklist(N);
       return SDValue(N, 0);
     }
   }
 
   // If this is a load followed by a store to the same location, then the store
   // is dead/noop.
   if (LoadSDNode *Ld = dyn_cast<LoadSDNode>(Value)) {
     if (Ld->getBasePtr() == Ptr && ST->getMemoryVT() == Ld->getMemoryVT() &&
-        ST->isUnindexed() && !ST->isVolatile() &&
+        ST->isUnindexed() && !ST->isVolatile() && !ST->isAtomic() &&
         // There can't be any side effects between the load and store, such as
         // a call or store.
         Chain.reachesChainWithoutSideEffects(SDValue(Ld, 1))) {
       // The store is dead, remove it.
       return Chain;
     }
   }
 
   if (StoreSDNode *ST1 = dyn_cast<StoreSDNode>(Chain)) {
-    if (ST->isUnindexed() && !ST->isVolatile() && ST1->isUnindexed() &&
-        !ST1->isVolatile()) {
+    if (ST->isUnindexed() && !ST->isVolatile() && !ST->isAtomic() &&
+        ST1->isUnindexed() && !ST1->isVolatile() && !ST1->isAtomic()) {
       if (ST1->getBasePtr() == Ptr && ST1->getValue() == Value &&
           ST->getMemoryVT() == ST1->getMemoryVT()) {
         // If this is a store followed by a store with the same value to the
         // same location, then the store is dead/noop.
         return Chain;
       }
 
       if (OptLevel != CodeGenOpt::None && ST1->hasOneUse() &&
while (!Chains.empty()) {
     case ISD::LIFETIME_END:
       // We can forward past any lifetime start/end that can be proven not to
       // alias the node.
       if (!isAlias(Chain.getNode(), N))
         Chains.push_back(Chain.getOperand(0));
       break;
     case ISD::STORE: {
       StoreSDNode *ST = dyn_cast<StoreSDNode>(Chain);
-      if (ST->isVolatile() || ST->isIndexed())
+      if (ST->isVolatile() || ST->isAtomic() || ST->isIndexed())
         continue;
       const BaseIndexOffset StoreBase = BaseIndexOffset::match(ST, DAG);
       // If we store purely within object bounds just before its lifetime ends,
       // we can remove the store.
       if (LifetimeEndBase.contains(DAG, LifetimeEnd->getSize() * 8, StoreBase,
                                    ST->getMemoryVT().getStoreSizeInBits())) {
         LLVM_DEBUG(dbgs() << "\nRemoving store:"; StoreBase.dump();
                    dbgs() << "\nwithin LIFETIME_END of : ";
SDValue DAGCombiner::visitINSERT_VECTOR_ELT(SDNode *N) {
 
   // Return the new vector
   return DAG.getBuildVector(VT, DL, Ops);
 }
 
 SDValue DAGCombiner::scalarizeExtractedVectorLoad(SDNode *EVE, EVT InVecVT,
                                                   SDValue EltNo,
                                                   LoadSDNode *OriginalLoad) {
-  assert(!OriginalLoad->isVolatile());
+  assert(!OriginalLoad->isVolatile() && !OriginalLoad->isAtomic());
 
   EVT ResultVT = EVE->getValueType(0);
   EVT VecEltVT = InVecVT.getVectorElementType();
   unsigned Align = OriginalLoad->getAlignment();
   unsigned NewAlign = DAG.getDataLayout().getABITypeAlignment(
       VecEltVT.getTypeForEVT(*DAG.getContext()));
 
   if (NewAlign > Align || !TLI.isOperationLegalOrCustom(ISD::LOAD, VecEltVT))
if (VecOp.getOpcode() == ISD::BITCAST) {
     ExtVT = BCVT.getVectorElementType();
   }
 
   // extract (vector load $addr), i --> load $addr + i * size
   if (!LegalOperations && !IndexC && VecOp.hasOneUse() &&
       ISD::isNormalLoad(VecOp.getNode()) &&
       !Index->hasPredecessor(VecOp.getNode())) {
     auto *VecLoad = dyn_cast<LoadSDNode>(VecOp);
-    if (VecLoad && !VecLoad->isVolatile())
+    if (VecLoad && !VecLoad->isVolatile() && !VecLoad->isAtomic())
       return scalarizeExtractedVectorLoad(N, VecVT, Index, VecLoad);
   }
 
   // Perform only after legalization to ensure build_vector / vector_shuffle
   // optimizations have already been done.
   if (!LegalOperations || !IndexC)
     return SDValue();
 
if (ISD::isNormalLoad(VecOp.getNode())) {
       LN0 = cast<LoadSDNode>(VecOp);
       Elt = (Idx < (int)NumElts) ? Idx : Idx - (int)NumElts;
       Index = DAG.getConstant(Elt, DL, Index.getValueType());
     }
   }
 
   // Make sure we found a non-volatile load and the extractelement is
   // the only use.
-  if (!LN0 || !LN0->hasNUsesOfValue(1,0) || LN0->isVolatile())
+  if (!LN0 || !LN0->hasNUsesOfValue(1,0) || LN0->isVolatile() ||
+      LN0->isAtomic())
     return SDValue();
 
   // If Idx was -1 above, Elt is going to be -1, so just return undef.
   if (Elt == -1)
     return DAG.getUNDEF(LVT);
 
   return scalarizeExtractedVectorLoad(N, VecVT, Index, LN0);
 }

 /// (extract_subvector (load wide vector)) --> (load narrow vector)
 static SDValue narrowExtractedVectorLoad(SDNode *Extract, SelectionDAG &DAG) {
   // TODO: Add support for big-endian. The offset calculation must be adjusted.
   if (DAG.getDataLayout().isBigEndian())
     return SDValue();
 
   auto *Ld = dyn_cast<LoadSDNode>(Extract->getOperand(0));
   auto *ExtIdx = dyn_cast<ConstantSDNode>(Extract->getOperand(1));
-  if (!Ld || Ld->getExtensionType() || Ld->isVolatile() || !ExtIdx)
+  if (!Ld || Ld->getExtensionType() || Ld->isVolatile() || Ld->isAtomic() ||
+      !ExtIdx)
     return SDValue();
 
   // Allow targets to opt-out.
   EVT VT = Extract->getValueType(0);
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   if (!TLI.shouldReduceLoadWidth(Ld, Ld->getExtensionType(), VT))
     return SDValue();
 
bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
   if (LHS.getOpcode() == ISD::LOAD) {
     LoadSDNode *LLD = cast<LoadSDNode>(LHS);
     LoadSDNode *RLD = cast<LoadSDNode>(RHS);
 
     // Token chains must be identical.
     if (LHS.getOperand(0) != RHS.getOperand(0) ||
         // Do not let this transformation reduce the number of volatile loads.
         LLD->isVolatile() || RLD->isVolatile() ||
+        // Be conservative for atomics for the moment
+        // TODO: This does appear to be legal for unordered atomics
+        LLD->isAtomic() || RLD->isAtomic() ||
         // FIXME: If either is a pre/post inc/dec load,
         // we'd need to split out the address adjustment.
         LLD->isIndexed() || RLD->isIndexed() ||
         // If this is an EXTLOAD, the VT's must match.
         LLD->getMemoryVT() != RLD->getMemoryVT() ||
         // If this is an EXTLOAD, the kind of extension must match.
         (LLD->getExtensionType() != RLD->getExtensionType() &&
          // The only exception is if one of the extensions is anyext.
SDValue DAGCombiner::buildSqrtEstimate(SDValue Op, SDNodeFlags Flags) {
   return buildSqrtEstimateImpl(Op, Flags, false);
 }
 
 /// Return true if there is any possibility that the two addresses overlap.
 bool DAGCombiner::isAlias(SDNode *Op0, SDNode *Op1) const {
 
   struct MemUseCharacteristics {
     bool IsVolatile;
+    bool IsAtomic;
     SDValue BasePtr;
     int64_t Offset;
     Optional<int64_t> NumBytes;
     MachineMemOperand *MMO;
   };
 
   auto getCharacteristics = [](SDNode *N) -> MemUseCharacteristics {
     if (const auto *LSN = dyn_cast<LSBaseSDNode>(N)) {
       int64_t Offset = 0;
       if (auto *C = dyn_cast<ConstantSDNode>(LSN->getOffset()))
         Offset = (LSN->getAddressingMode() == ISD::PRE_INC)
                      ? C->getSExtValue()
                      : (LSN->getAddressingMode() == ISD::PRE_DEC)
                            ? -1 * C->getSExtValue()
                            : 0;
-      return {LSN->isVolatile(), LSN->getBasePtr(), Offset /*base offset*/,
+      return {LSN->isVolatile(), LSN->isAtomic(), LSN->getBasePtr(),
+              Offset /*base offset*/,
               Optional<int64_t>(LSN->getMemoryVT().getStoreSize()),
               LSN->getMemOperand()};
     }
     if (const auto *LN = cast<LifetimeSDNode>(N))
-      return {false /*isVolatile*/, LN->getOperand(1),
+      return {false /*isVolatile*/, /*isAtomic*/ false, LN->getOperand(1),
               (LN->hasOffset()) ? LN->getOffset() : 0,
               (LN->hasOffset()) ? Optional<int64_t>(LN->getSize())
                                 : Optional<int64_t>(),
               (MachineMemOperand *)nullptr};
     // Default.
-    return {false /*isvolatile*/, SDValue(), (int64_t)0 /*offset*/,
+    return {false /*isvolatile*/, /*isAtomic*/ false, SDValue(),
+            (int64_t)0 /*offset*/,
             Optional<int64_t>() /*size*/, (MachineMemOperand *)nullptr};
   };
 
   MemUseCharacteristics MUC0 = getCharacteristics(Op0),
                         MUC1 = getCharacteristics(Op1);
 
   // If they are to the same address, then they must be aliases.
   if (MUC0.BasePtr.getNode() && MUC0.BasePtr == MUC1.BasePtr &&
       MUC0.Offset == MUC1.Offset)
     return true;
 
   // If they are both volatile then they cannot be reordered.
   if (MUC0.IsVolatile && MUC1.IsVolatile)
     return true;
 
+  // Be conservative about atomics for the moment
+  // TODO: this is way overconservative for unordered atomics
+  if (MUC0.IsAtomic && MUC1.IsAtomic)
+    return true;
+
   if (MUC0.MMO && MUC1.MMO) {
     if ((MUC0.MMO->isInvariant() && MUC1.MMO->isStore()) ||
         (MUC1.MMO->isInvariant() && MUC0.MMO->isStore()))
       return false;
   }
 
   // Try to prove that there is aliasing, or that there is no aliasing. Either
   // way, we can return now. If nothing can be proved, proceed with more tests.

 /// Walk up chain skipping non-aliasing memory nodes,
 /// looking for aliasing nodes and adding them to the Aliases vector.
 void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain,
                                    SmallVectorImpl<SDValue> &Aliases) {
   SmallVector<SDValue, 8> Chains;     // List of chains to visit.
   SmallPtrSet<SDNode *, 16> Visited;  // Visited node set.
 
   // Get alias information for node.
-  const bool IsLoad = isa<LoadSDNode>(N) && !cast<LoadSDNode>(N)->isVolatile();
+  const bool IsLoad = isa<LoadSDNode>(N) &&
+    !cast<LoadSDNode>(N)->isVolatile() && !cast<LoadSDNode>(N)->isAtomic();
 
   // Starting off.
   Chains.push_back(OriginalChain);
   unsigned Depth = 0;
 
   // Attempt to improve chain by a single step
   std::function<bool(SDValue &)> ImproveChain = [&](SDValue &C) -> bool {
     switch (C.getOpcode()) {
     case ISD::EntryToken:
       // No need to mark EntryToken.
       C = SDValue();
       return true;
     case ISD::LOAD:
     case ISD::STORE: {
       // Get alias information for C.
       bool IsOpLoad = isa<LoadSDNode>(C.getNode()) &&
-                      !cast<LSBaseSDNode>(C.getNode())->isVolatile();
+                      !cast<LSBaseSDNode>(C.getNode())->isVolatile() &&
+                      !cast<LSBaseSDNode>(C.getNode())->isAtomic();
       if ((IsLoad && IsOpLoad) || !isAlias(N, C.getNode())) {
         // Look further up the chain.
         C = C.getOperand(0);
         return true;
       }
       // Alias, so stop here.
       return false;
     }
bool DAGCombiner::parallelizeChainedStores(StoreSDNode *St) {
 
   // Add ST's interval.
   Intervals.insert(0, (St->getMemoryVT().getSizeInBits() + 7) / 8, Unit);
 
   while (StoreSDNode *Chain = dyn_cast<StoreSDNode>(STChain->getChain())) {
     // If the chain has more than one use, then we can't reorder the mem ops.
     if (!SDValue(Chain, 0)->hasOneUse())
       break;
-    if (Chain->isVolatile() || Chain->isIndexed())
+    if (Chain->isVolatile() || Chain->isAtomic() || Chain->isIndexed())
       break;
 
     // Find the base pointer and offset for this memory node.
     const BaseIndexOffset Ptr = BaseIndexOffset::match(Chain, DAG);
     // Check that the base pointer is the same as the original one.
     int64_t Offset;
     if (!BasePtr.equalBaseIndex(Ptr, DAG, Offset))
       break;

lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

SDValue DAGTypeLegalizer::GenWidenVectorLoads(SmallVectorImpl<SDValue> &LdChain,
   SDValue Chain = LD->getChain();
   SDValue BasePtr = LD->getBasePtr();
   unsigned Align = LD->getAlignment();
   MachineMemOperand::Flags MMOFlags = LD->getMemOperand()->getFlags();
   AAMDNodes AAInfo = LD->getAAInfo();
 
   int LdWidth = LdVT.getSizeInBits();
   int WidthDiff = WidenWidth - LdWidth;
-  unsigned LdAlign = LD->isVolatile() ? 0 : Align; // Allow wider loads.
+  unsigned LdAlign = (LD->isVolatile() || LD->isAtomic()) ? 0 : Align; // Allow wider loads.
 
   // Find the vector type that can load from.
   EVT NewVT = FindMemType(DAG, TLI, LdWidth, WidenVT, LdAlign, WidthDiff);
   int NewVTWidth = NewVT.getSizeInBits();
   SDValue LdOp = DAG.getLoad(NewVT, dl, Chain, BasePtr, LD->getPointerInfo(),
                              Align, MMOFlags, AAInfo);
   LdChain.push_back(LdOp.getValue(1));
 

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

if (getOpcode() == ISD::TokenFactor) {
     // reaches Dest.
     return llvm::all_of((*this)->ops(), [=](SDValue Op) {
       return Op.reachesChainWithoutSideEffects(Dest, Depth - 1);
     });
   }
 
   // Loads don't have side effects, look through them.
   if (LoadSDNode *Ld = dyn_cast<LoadSDNode>(*this)) {
-    if (!Ld->isVolatile())
+    if (Ld->isUnordered())
       return Ld->getChain().reachesChainWithoutSideEffects(Dest, Depth-1);
   }
   return false;
 }
 
 bool SDNode::hasPredecessor(const SDNode *N) const {
   SmallPtrSet<const SDNode *, 32> Visited;
   SmallVector<const SDNode *, 16> Worklist;

 }
 
 bool SelectionDAG::areNonVolatileConsecutiveLoads(LoadSDNode *LD,
                                                   LoadSDNode *Base,
                                                   unsigned Bytes,
                                                   int Dist) const {
   if (LD->isVolatile() || Base->isVolatile())
     return false;
+  // TODO: probably too restrictive for atomics, revisit
+  if (LD->isAtomic() || Base->isAtomic())
+    return false;
   if (LD->isIndexed() || Base->isIndexed())
     return false;
   if (LD->getChain() != Base->getChain())
     return false;
   EVT VT = LD->getValueType(0);
   if (VT.getSizeInBits() / 8 != Bytes)
     return false;
 

lib/CodeGen/SelectionDAG/TargetLowering.cpp

if (DCI.isBeforeLegalize() &&
         N0.getOpcode() == ISD::AND && C1 == 0 &&
         N0.getNode()->hasOneUse() &&
         isa<LoadSDNode>(N0.getOperand(0)) &&
         N0.getOperand(0).getNode()->hasOneUse() &&
         isa<ConstantSDNode>(N0.getOperand(1))) {
       LoadSDNode *Lod = cast<LoadSDNode>(N0.getOperand(0));
       APInt bestMask;
       unsigned bestWidth = 0, bestOffset = 0;
-      if (!Lod->isVolatile() && Lod->isUnindexed()) {
+      if (!Lod->isVolatile() && !Lod->isAtomic() && Lod->isUnindexed()) {
         unsigned origWidth = N0.getValueSizeInBits();
         unsigned maskWidth = origWidth;
         // We can narrow (e.g.) 16-bit extending loads on 32-bit target to
         // 8 bits, but have to be careful...
         if (Lod->getExtensionType() != ISD::NON_EXTLOAD)
           origWidth = Lod->getMemoryVT().getSizeInBits();
         const APInt &Mask = N0.getConstantOperandAPInt(1);
         for (unsigned width = origWidth / 2; width>=8; width /= 2) {