[PPC] Lower load acquire/seq_cst trailing fence to cmp + bne + isync.

[timshen]

Summary

This fixes pr32392.

The lowering pipeline is:
llvm.ppc.cfence in IR -> PPC::CFENCE8 in isel -> Actual instructions in expandPostRAPseudo.

The reason why expandPostRAPseudo is chosen is because previous passes are likely eliminating instructions like cmpw 3, 3 (early CSE) and bne- 7, .+4 (some branch pass(s)).

[kbarton]

llvm/lib/Target/PowerPC/PPCInstr64Bit.td

967

Do we also need to mark Uses = [CR7]?

llvm/test/CodeGen/PowerPC/atomic-2.ll

111–114

Please add a reg expression here to ensure the registers used by the compare are the same as the ones in the ld above (this is necessary for correctness of the isync).

113

Please add CHECK-NEXT for the bne- and isync instructions. We want to ensure the cmp, bc, isync instructions stay together.

llvm/test/CodeGen/PowerPC/atomics-indexed.ll

14

Same comments as above for reg expression and CHECK-NEXT

25

And here as well

llvm/test/CodeGen/PowerPC/atomics.ll

31

And here as well.

44

And last but not least... :)

[timshen]

llvm/test/CodeGen/PowerPC/atomic-2.ll

113

I'm not sure about that.

LLVM post-RA scheduler may stick instructions in between the cmp, bc, isync sequence, but the dependencies introduced by cmp and bc are perfectly preserved.

[timshen]

llvm/lib/Target/PowerPC/PPCInstr64Bit.td

967

I'm not sure - what does Uses exactly mean?

I didn't add, because a search for "clobbers" in PPCInstr64Bit.td gives me examples that clobbers are added through "Defs" without "Uses".

[timshen]

Rebase onto D32762.

Add associated register numbers in CHECK lines, but still doesn't use CHECK-NEXT as I commented.

[timshen]

Rebase onto the AtomicExpandPass change.

[kbarton]

llvm/test/CodeGen/PowerPC/atomic-2.ll

113

OK, that's fair. I've verified with the hardware designers that this sequence can have unrelated instructions interleaved.
However, we also want to check that any operations we are trying to order using the sync are not moved across this sequence. Can you add a use of VAL to the test and a check to ensure it doesn't get moved up past the isync?

[timshen]

Add test case for ordering requirement.

[timshen]

llvm/test/CodeGen/PowerPC/atomic-2.ll

113

Added I "test_ordering" into atomics-regression.ll.

I noticed that, according to the C++ load-acquire semantics (I assume that it's similar to LLVM's load-acquire), a succeeding load should never be scheduled across the previous load-acquire.

[timshen]

Add a test case for store to an unrelated location after load.

[kbarton]

LGTM.
Thanks for adding the additional test case!

llvm/lib/Target/PowerPC/PPCInstr64Bit.td

967

Yeah, I just verified this with Nemanja. We want to use the Def to mark it as clobbered. The Use of CR7 is internal to this pseudo instruction, but there is no way to indicate that. So if we mark this with an explicit use of CR7, the machinery may try to find the definition of that but won't consider the fact that this instruction is defining it also.

llvm/include/llvm/IR/IntrinsicsPowerPC.td

def int_ppc_tendall : GCCBuiltin<"__builtin_tendall">,
       Intrinsic<[llvm_i32_ty], [], []>;
 def int_ppc_tresume : GCCBuiltin<"__builtin_tresume">,
       Intrinsic<[llvm_i32_ty], [], []>;
 def int_ppc_tsuspend : GCCBuiltin<"__builtin_tsuspend">,
       Intrinsic<[llvm_i32_ty], [], []>;
 
 def int_ppc_ttest : GCCBuiltin<"__builtin_ttest">,
       Intrinsic<[llvm_i64_ty], [], []>;
+
+def int_ppc_cfence : Intrinsic<[], [llvm_anyint_ty], []>;
 }

llvm/lib/Target/PowerPC/PPCISelLowering.h

private:
     SDValue LowerSHL_PARTS(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSRL_PARTS(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSRA_PARTS(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerINSERT_VECTOR_ELT(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerEXTRACT_VECTOR_ELT(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerINTRINSIC_WO_CHAIN(SDValue Op, SelectionDAG &DAG) const;
+    SDValue LowerINTRINSIC_VOID(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSCALAR_TO_VECTOR(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSIGN_EXTEND_INREG(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerMUL(SDValue Op, SelectionDAG &DAG) const;
 
     SDValue LowerVectorLoad(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerVectorStore(SDValue Op, SelectionDAG &DAG) const;
 
     SDValue LowerCallResult(SDValue Chain, SDValue InFlag,

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
   setOperationAction(ISD::EH_DWARF_CFA, MVT::i64, Custom);
 
   // We want to custom lower some of our intrinsics.
   setOperationAction(ISD::INTRINSIC_WO_CHAIN, MVT::Other, Custom);
 
   // To handle counter-based loop conditions.
   setOperationAction(ISD::INTRINSIC_W_CHAIN, MVT::i1, Custom);
 
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::i8, Custom);
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::i16, Custom);
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::i32, Custom);
+  setOperationAction(ISD::INTRINSIC_VOID, MVT::Other, Custom);
+
   // Comparisons that require checking two conditions.
   setCondCodeAction(ISD::SETULT, MVT::f32, Expand);
   setCondCodeAction(ISD::SETULT, MVT::f64, Expand);
   setCondCodeAction(ISD::SETUGT, MVT::f32, Expand);
   setCondCodeAction(ISD::SETUGT, MVT::f64, Expand);
   setCondCodeAction(ISD::SETUEQ, MVT::f32, Expand);
   setCondCodeAction(ISD::SETUEQ, MVT::f64, Expand);
   setCondCodeAction(ISD::SETOGE, MVT::f32, Expand);
SDValue PPCTargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
 
   // If we are supposed to, toggle the bit.
   if (InvertBit)
     Flags = DAG.getNode(ISD::XOR, dl, MVT::i32, Flags,
                         DAG.getConstant(1, dl, MVT::i32));
   return Flags;
 }
 
+SDValue PPCTargetLowering::LowerINTRINSIC_VOID(SDValue Op,
+                                               SelectionDAG &DAG) const {
+  // SelectionDAGBuilder::visitTargetIntrinsic may insert one extra chain to
+  // the beginning of the argument list.
+  int ArgStart = isa<ConstantSDNode>(Op.getOperand(0)) ? 0 : 1;
+  SDLoc DL(Op);
+  switch (cast<ConstantSDNode>(Op.getOperand(ArgStart))->getZExtValue()) {
+  case Intrinsic::ppc_cfence: {
+    assert(Subtarget.isPPC64() && "Only 64-bit is supported for now.");
+    return SDValue(DAG.getMachineNode(PPC::CFENCE8, DL, MVT::Other,
+                                      DAG.getNode(ISD::ANY_EXTEND, DL, MVT::i64,
+                                                  Op.getOperand(ArgStart + 1))),
+                   0);
+  }
+  default:
+    break;
+  }
+  return SDValue();
+}
+
 SDValue PPCTargetLowering::LowerSIGN_EXTEND_INREG(SDValue Op,
                                                   SelectionDAG &DAG) const {
   SDLoc dl(Op);
   // For v2i64 (VSX), we can pattern patch the v2i32 case (using fp <-> int
   // instructions), but for smaller types, we need to first extend up to v2i32
   // before doing going farther.
   if (Op.getValueType() == MVT::v2i64) {
     EVT ExtVT = cast<VTSDNode>(Op.getOperand(1))->getVT();
SDValue PPCTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::MUL:                return LowerMUL(Op, DAG);
 
   // For counter-based loop handling.
   case ISD::INTRINSIC_W_CHAIN:  return SDValue();
 
   // Frame & Return address.
   case ISD::RETURNADDR:         return LowerRETURNADDR(Op, DAG);
   case ISD::FRAMEADDR:          return LowerFRAMEADDR(Op, DAG);
+
+  case ISD::INTRINSIC_VOID:
+    return LowerINTRINSIC_VOID(Op, DAG);
   }
 }
 
 void PPCTargetLowering::ReplaceNodeResults(SDNode *N,
                                            SmallVectorImpl<SDValue>&Results,
                                            SelectionDAG &DAG) const {
   SDLoc dl(N);
   switch (N->getOpcode()) {
Instruction *PPCTargetLowering::emitLeadingFence(IRBuilder<> &Builder,
   if (isReleaseOrStronger(Ord))
     return callIntrinsic(Builder, Intrinsic::ppc_lwsync);
   return nullptr;
 }
 
 Instruction *PPCTargetLowering::emitTrailingFence(IRBuilder<> &Builder,
                                                   Instruction *Inst,
                                                   AtomicOrdering Ord) const {
-  if (Inst->isAtomicLoad() && isAcquireOrStronger(Ord))
-    return callIntrinsic(Builder, Intrinsic::ppc_lwsync);
-  // FIXME: this is too conservative, a dependent branch + isync is enough.
+  if (Inst->isAtomicLoad() && isAcquireOrStronger(Ord)) {
     // See http://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html and
     // http://www.rdrop.com/users/paulmck/scalability/paper/N2745r.2011.03.04a.html
     // and http://www.cl.cam.ac.uk/~pes20/cppppc/ for justification.
+    if (isa<LoadInst>(Inst) && Subtarget.isPPC64())
+      return Builder.CreateCall(
+          Intrinsic::getDeclaration(
+              Builder.GetInsertBlock()->getParent()->getParent(),
+              Intrinsic::ppc_cfence, {Inst->getType()}),
+          {Inst});
+    // FIXME: Can use isync for rmw operation.
+    return callIntrinsic(Builder, Intrinsic::ppc_lwsync);
+  }
   return nullptr;
 }
 
 MachineBasicBlock *
 PPCTargetLowering::EmitAtomicBinary(MachineInstr &MI, MachineBasicBlock *BB,
                                     unsigned AtomicSize,
                                     unsigned BinOpcode,
                                     unsigned CmpOpcode,

llvm/lib/Target/PowerPC/PPCInstr64Bit.td

def ADDISgotTprelHA: Pseudo<(outs g8rc:$rD), (ins g8rc_nox0:$reg, s16imm64:$disp),
                            (PPCaddisGotTprelHA i64:$reg,
                                                tglobaltlsaddr:$disp))]>,
                   isPPC64;
 def LDgotTprelL: Pseudo<(outs g8rc:$rD), (ins s16imm64:$disp, g8rc_nox0:$reg),
                         "#LDgotTprelL",
                         [(set i64:$rD,
                           (PPCldGotTprelL tglobaltlsaddr:$disp, i64:$reg))]>,
                  isPPC64;
+
+let isBarrier = 1, isPseudo = 1, Defs = [CR7], Itinerary = IIC_LdStSync in
+def CFENCE8 : Pseudo<(outs), (ins g8rc:$cr), "#CFENCE8", []>;
+
 def : Pat<(PPCaddTls i64:$in, tglobaltlsaddr:$g),
           (ADD8TLS $in, tglobaltlsaddr:$g)>;
 def ADDIStlsgdHA: Pseudo<(outs g8rc:$rD), (ins g8rc_nox0:$reg, s16imm64:$disp),
                          "#ADDIStlsgdHA",
                          [(set i64:$rD,
                            (PPCaddisTlsgdHA i64:$reg, tglobaltlsaddr:$disp))]>,
                   isPPC64;
 def ADDItlsgdL : Pseudo<(outs g8rc:$rD), (ins g8rc_nox0:$reg, s16imm64:$disp),

llvm/lib/Target/PowerPC/PPCInstrInfo.cpp

static const std::pair<unsigned, const char *> TargetFlags[] = {
       {MO_PLT, "ppc-plt"},
       {MO_PIC_FLAG, "ppc-pic"},
       {MO_NLP_FLAG, "ppc-nlp"},
       {MO_NLP_HIDDEN_FLAG, "ppc-nlp-hidden"}};
   return makeArrayRef(TargetFlags);
 }
 
 bool PPCInstrInfo::expandPostRAPseudo(MachineInstr &MI) const {
+  auto &MBB = *MI.getParent();
+  auto DL = MI.getDebugLoc();
   switch (MI.getOpcode()) {
   case TargetOpcode::LOAD_STACK_GUARD: {
     assert(Subtarget.isTargetLinux() &&
            "Only Linux target is expected to contain LOAD_STACK_GUARD");
     const int64_t Offset = Subtarget.isPPC64() ? -0x7010 : -0x7008;
     const unsigned Reg = Subtarget.isPPC64() ? PPC::X13 : PPC::R2;
     MI.setDesc(get(Subtarget.isPPC64() ? PPC::LD : PPC::LWZ));
     MachineInstrBuilder(*MI.getParent()->getParent(), MI)
case PPC::DFSTOREf64: {
     if ((TargetReg >= PPC::F0 && TargetReg <= PPC::F31) ||
         (TargetReg >= PPC::VSL0 && TargetReg <= PPC::VSL31))
       Opcode = LowerOpcode;
     else
       Opcode = UpperOpcode;
     MI.setDesc(get(Opcode));
     return true;
   }
+  case PPC::CFENCE8: {
+    auto Val = MI.getOperand(0).getReg();
+    BuildMI(MBB, MI, DL, get(PPC::CMPW), PPC::CR7).addReg(Val).addReg(Val);
+    BuildMI(MBB, MI, DL, get(PPC::CTRL_DEP))
+        .addImm(PPC::PRED_NE_MINUS)
+        .addReg(PPC::CR7)
+        .addImm(1);
+    MI.setDesc(get(PPC::ISYNC));
+    MI.RemoveOperand(0);
+    return true;
+  }
   }
   return false;
 }
 
 const TargetRegisterClass *
 PPCInstrInfo::updatedRC(const TargetRegisterClass *RC) const {
   if (Subtarget.hasVSX() && RC == &PPC::VRRCRegClass)
     return &PPC::VSRCRegClass;
   return RC;
 }

llvm/lib/Target/PowerPC/PPCInstrInfo.td

let isBranch = 1, isTerminator = 1, hasCtrlDep = 1, PPC970_Unit = 7 in {
   def BA  : IForm<18, 1, 0, (outs), (ins absdirectbrtarget:$dst),
                   "ba $dst", IIC_BrB, []>;
   }
 
   // BCC represents an arbitrary conditional branch on a predicate.
   // FIXME: should be able to write a pattern for PPCcondbranch, but can't use
   // a two-value operand where a dag node expects two operands. :(
   let isCodeGenOnly = 1 in {
-    def BCC : BForm<16, 0, 0, (outs), (ins pred:$cond, condbrtarget:$dst),
+    class BCC_class : BForm<16, 0, 0, (outs), (ins pred:$cond, condbrtarget:$dst),
                             "b${cond:cc}${cond:pm} ${cond:reg}, $dst"
                             /*[(PPCcondbranch crrc:$crS, imm:$opc, bb:$dst)]*/>;
+    def BCC : BCC_class;
+
+    // The same as BCC, except that it's not a terminator. Used for introducing
+    // control flow dependency without creating new blocks.
+    let isTerminator = 0 in def CTRL_DEP : BCC_class;
+
     def BCCA : BForm<16, 1, 0, (outs), (ins pred:$cond, abscondbrtarget:$dst),
                      "b${cond:cc}a${cond:pm} ${cond:reg}, $dst">;
 
     let isReturn = 1, Uses = [LR, RM] in
     def BCCLR : XLForm_2_br<19, 16, 0, (outs), (ins pred:$cond),
                            "b${cond:cc}lr${cond:pm} ${cond:reg}", IIC_BrB, []>;
   }
 

llvm/test/CodeGen/PowerPC/atomic-2.ll

; CHECK: std
   ret void
 }
 
 define i64 @atomic_load(i64* %mem) nounwind {
 entry:
 ; CHECK: @atomic_load
   %tmp = load atomic i64, i64* %mem acquire, align 64
 ; CHECK-NOT: ldarx
-; CHECK: ld
-; CHECK: lwsync
+; CHECK: ld [[VAL:[0-9]+]]
+; CHECK: cmpw [[CR:[0-9]+]], [[VAL]], [[VAL]]
+; CHECK: bne- [[CR]], .+4
+; CHECK: isync
   ret i64 %tmp
 }
 

llvm/test/CodeGen/PowerPC/atomics-indexed.ll

 ; RUN: llc < %s -mtriple=powerpc-apple-darwin -march=ppc32 -verify-machineinstrs | FileCheck %s --check-prefix=CHECK --check-prefix=PPC32
 ; FIXME: -verify-machineinstrs currently fail on ppc64 (mismatched register/instruction).
 ; This is already checked for in Atomics-64.ll
 ; RUN: llc < %s -mtriple=powerpc-apple-darwin -march=ppc64 | FileCheck %s --check-prefix=CHECK --check-prefix=PPC64
 
 ; In this file, we check that atomic load/store can make use of the indexed
 ; versions of the instructions.
 
 ; Indexed version of loads
 define i8 @load_x_i8_seq_cst([100000 x i8]* %mem) {
 ; CHECK-LABEL: load_x_i8_seq_cst
 ; CHECK: sync
-; CHECK: lbzx
-; CHECK: lwsync
+; CHECK: lbzx [[VAL:r[0-9]+]]
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   %ptr = getelementptr inbounds [100000 x i8], [100000 x i8]* %mem, i64 0, i64 90000
   %val = load atomic i8, i8* %ptr seq_cst, align 1
   ret i8 %val
 }
 define i16 @load_x_i16_acquire([100000 x i16]* %mem) {
 ; CHECK-LABEL: load_x_i16_acquire
-; CHECK: lhzx
-; CHECK: lwsync
+; CHECK: lhzx [[VAL:r[0-9]+]]
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   %ptr = getelementptr inbounds [100000 x i16], [100000 x i16]* %mem, i64 0, i64 90000
   %val = load atomic i16, i16* %ptr acquire, align 2
   ret i16 %val
 }
 define i32 @load_x_i32_monotonic([100000 x i32]* %mem) {
 ; CHECK-LABEL: load_x_i32_monotonic
 ; CHECK: lwzx
 ; CHECK-NOT: sync

llvm/test/CodeGen/PowerPC/atomics-regression.ll

; PPC64LE-NEXT:    blr
   %val = load atomic i8, i8* %ptr monotonic, align 1
   ret i8 %val
 }
 
 define i8 @test2(i8* %ptr) {
 ; PPC64LE-LABEL: test2:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    lbz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i8, i8* %ptr acquire, align 1
   ret i8 %val
 }
 
 define i8 @test3(i8* %ptr) {
 ; PPC64LE-LABEL: test3:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    lbz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i8, i8* %ptr seq_cst, align 1
   ret i8 %val
 }
 
 define i16 @test4(i16* %ptr) {
 ; PPC64LE-LABEL: test4:
 ; PPC64LE:       # BB#0:
; PPC64LE-NEXT:    blr
   %val = load atomic i16, i16* %ptr monotonic, align 2
   ret i16 %val
 }
 
 define i16 @test6(i16* %ptr) {
 ; PPC64LE-LABEL: test6:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    lhz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i16, i16* %ptr acquire, align 2
   ret i16 %val
 }
 
 define i16 @test7(i16* %ptr) {
 ; PPC64LE-LABEL: test7:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    lhz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i16, i16* %ptr seq_cst, align 2
   ret i16 %val
 }
 
 define i32 @test8(i32* %ptr) {
 ; PPC64LE-LABEL: test8:
 ; PPC64LE:       # BB#0:
; PPC64LE-NEXT:    blr
   %val = load atomic i32, i32* %ptr monotonic, align 4
   ret i32 %val
 }
 
 define i32 @test10(i32* %ptr) {
 ; PPC64LE-LABEL: test10:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    lwz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i32, i32* %ptr acquire, align 4
   ret i32 %val
 }
 
 define i32 @test11(i32* %ptr) {
 ; PPC64LE-LABEL: test11:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    lwz 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i32, i32* %ptr seq_cst, align 4
   ret i32 %val
 }
 
 define i64 @test12(i64* %ptr) {
 ; PPC64LE-LABEL: test12:
 ; PPC64LE:       # BB#0:
; PPC64LE-NEXT:    blr
   %val = load atomic i64, i64* %ptr monotonic, align 8
   ret i64 %val
 }
 
 define i64 @test14(i64* %ptr) {
 ; PPC64LE-LABEL: test14:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    ld 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i64, i64* %ptr acquire, align 8
   ret i64 %val
 }
 
 define i64 @test15(i64* %ptr) {
 ; PPC64LE-LABEL: test15:
 ; PPC64LE:       # BB#0:
 ; PPC64LE-NEXT:    sync
 ; PPC64LE-NEXT:    ori 2, 2, 0
 ; PPC64LE-NEXT:    ld 3, 0(3)
-; PPC64LE-NEXT:    lwsync
+; PPC64LE-NEXT:    cmpw 7, 3, 3
+; PPC64LE-NEXT:    bne- 7, .+4
+; PPC64LE-NEXT:    isync
 ; PPC64LE-NEXT:    blr
   %val = load atomic i64, i64* %ptr seq_cst, align 8
   ret i64 %val
 }
 
 define void @test16(i8* %ptr, i8 %val) {
 ; PPC64LE-LABEL: test16:
 ; PPC64LE:       # BB#0:

llvm/test/CodeGen/PowerPC/atomics.ll

 ; CHECK-LABEL: load_i16_monotonic
 ; CHECK: lhz
 ; CHECK-NOT: sync
   %val = load atomic i16, i16* %mem monotonic, align 2
   ret i16 %val
 }
 define i32 @load_i32_acquire(i32* %mem) {
 ; CHECK-LABEL: load_i32_acquire
-; CHECK: lwz
+; CHECK: lwz [[VAL:r[0-9]+]]
   %val = load atomic i32, i32* %mem acquire, align 4
-; CHECK: lwsync
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   ret i32 %val
 }
 define i64 @load_i64_seq_cst(i64* %mem) {
 ; CHECK-LABEL: load_i64_seq_cst
 ; CHECK: sync
 ; PPC32: __sync_
 ; PPC64-NOT: __sync_
-; PPC64: ld
+; PPC64: ld [[VAL:r[0-9]+]]
   %val = load atomic i64, i64* %mem seq_cst, align 8
-; CHECK: lwsync
+; CHECK-PPC32: lwsync
+; CHECK-PPC64: cmpw [[CR:cr[0-9]+]], [[VAL]], [[VAL]]
+; CHECK-PPC64: bne- [[CR]], .+4
+; CHECK-PPC64: isync
   ret i64 %val
 }
 
 ; Stores
 define void @store_i8_unordered(i8* %mem) {
 ; CHECK-LABEL: store_i8_unordered
 ; CHECK-NOT: sync
 ; CHECK: stb