diff --git a/llvm/lib/Target/ARC/ARCISelLowering.cpp b/llvm/lib/Target/ARC/ARCISelLowering.cpp
index 5d9a366f5ed54..fb1a42440498a 100644
--- a/llvm/lib/Target/ARC/ARCISelLowering.cpp
+++ b/llvm/lib/Target/ARC/ARCISelLowering.cpp
@@ -174,6 +174,8 @@ ARCTargetLowering::ARCTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::READCYCLECOUNTER, MVT::i32, Legal);
   setOperationAction(ISD::READCYCLECOUNTER, MVT::i64,
                      isTypeLegal(MVT::i64) ? Legal : Custom);
+
+  setMaxAtomicSizeInBitsSupported(0);
 }
 
 const char *ARCTargetLowering::getTargetNodeName(unsigned Opcode) const {
diff --git a/llvm/lib/Target/ARC/ARCTargetMachine.cpp b/llvm/lib/Target/ARC/ARCTargetMachine.cpp
index d4ae3255b32ab..4f612ae623b98 100644
--- a/llvm/lib/Target/ARC/ARCTargetMachine.cpp
+++ b/llvm/lib/Target/ARC/ARCTargetMachine.cpp
@@ -57,6 +57,7 @@ class ARCPassConfig : public TargetPassConfig {
     return getTM<ARCTargetMachine>();
   }
 
+  void addIRPasses() override;
   bool addInstSelector() override;
   void addPreEmitPass() override;
   void addPreRegAlloc() override;
@@ -68,6 +69,12 @@ TargetPassConfig *ARCTargetMachine::createPassConfig(PassManagerBase &PM) {
   return new ARCPassConfig(*this, PM);
 }
 
+void ARCPassConfig::addIRPasses() {
+  addPass(createAtomicExpandPass());
+
+  TargetPassConfig::addIRPasses();
+}
+
 bool ARCPassConfig::addInstSelector() {
   addPass(createARCISelDag(getARCTargetMachine(), getOptLevel()));
   return false;
diff --git a/llvm/lib/Target/BPF/BPFISelLowering.cpp b/llvm/lib/Target/BPF/BPFISelLowering.cpp
index 2fe86e75ddae8..4d8ace7c1ece0 100644
--- a/llvm/lib/Target/BPF/BPFISelLowering.cpp
+++ b/llvm/lib/Target/BPF/BPFISelLowering.cpp
@@ -151,6 +151,7 @@ BPFTargetLowering::BPFTargetLowering(const TargetMachine &TM,
   }
 
   setBooleanContents(ZeroOrOneBooleanContent);
+  setMaxAtomicSizeInBitsSupported(64);
 
   // Function alignments
   setMinFunctionAlignment(Align(8));
diff --git a/llvm/lib/Target/BPF/BPFTargetMachine.cpp b/llvm/lib/Target/BPF/BPFTargetMachine.cpp
index ab0db576f7f72..7c83225c5d934 100644
--- a/llvm/lib/Target/BPF/BPFTargetMachine.cpp
+++ b/llvm/lib/Target/BPF/BPFTargetMachine.cpp
@@ -148,7 +148,9 @@ void BPFTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB) {
 }
 
 void BPFPassConfig::addIRPasses() {
+  addPass(createAtomicExpandPass());
   addPass(createBPFCheckAndAdjustIR());
+
   TargetPassConfig::addIRPasses();
 }
 
diff --git a/llvm/lib/Target/Lanai/LanaiISelLowering.cpp b/llvm/lib/Target/Lanai/LanaiISelLowering.cpp
index cbb5c2b998e27..7e6235942619c 100644
--- a/llvm/lib/Target/Lanai/LanaiISelLowering.cpp
+++ b/llvm/lib/Target/Lanai/LanaiISelLowering.cpp
@@ -166,6 +166,8 @@ LanaiTargetLowering::LanaiTargetLowering(const TargetMachine &TM,
 
   // Booleans always contain 0 or 1.
   setBooleanContents(ZeroOrOneBooleanContent);
+
+  setMaxAtomicSizeInBitsSupported(0);
 }
 
 SDValue LanaiTargetLowering::LowerOperation(SDValue Op,
diff --git a/llvm/lib/Target/Lanai/LanaiTargetMachine.cpp b/llvm/lib/Target/Lanai/LanaiTargetMachine.cpp
index 039182b3ffe60..33479720183b4 100644
--- a/llvm/lib/Target/Lanai/LanaiTargetMachine.cpp
+++ b/llvm/lib/Target/Lanai/LanaiTargetMachine.cpp
@@ -93,6 +93,7 @@ class LanaiPassConfig : public TargetPassConfig {
     return getTM<LanaiTargetMachine>();
   }
 
+  void addIRPasses() override;
   bool addInstSelector() override;
   void addPreSched2() override;
   void addPreEmitPass() override;
@@ -104,6 +105,12 @@ LanaiTargetMachine::createPassConfig(PassManagerBase &PassManager) {
   return new LanaiPassConfig(*this, &PassManager);
 }
 
+void LanaiPassConfig::addIRPasses() {
+  addPass(createAtomicExpandPass());
+
+  TargetPassConfig::addIRPasses();
+}
+
 // Install an instruction selector pass.
 bool LanaiPassConfig::addInstSelector() {
   addPass(createLanaiISelDag(getLanaiTargetMachine()));
diff --git a/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp b/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
index ee7762c296bf5..9422bcca2299e 100644
--- a/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
+++ b/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
@@ -333,6 +333,7 @@ MSP430TargetLowering::MSP430TargetLowering(const TargetMachine &TM,
 
   setMinFunctionAlignment(Align(2));
   setPrefFunctionAlignment(Align(2));
+  setMaxAtomicSizeInBitsSupported(0);
 }
 
 SDValue MSP430TargetLowering::LowerOperation(SDValue Op,
diff --git a/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp b/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp
index 39e0658eb70dd..283de46e57d5c 100644
--- a/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp
+++ b/llvm/lib/Target/MSP430/MSP430TargetMachine.cpp
@@ -65,6 +65,7 @@ class MSP430PassConfig : public TargetPassConfig {
     return getTM<MSP430TargetMachine>();
   }
 
+  void addIRPasses() override;
   bool addInstSelector() override;
   void addPreEmitPass() override;
 };
@@ -81,6 +82,12 @@ MachineFunctionInfo *MSP430TargetMachine::createMachineFunctionInfo(
                                                                       F, STI);
 }
 
+void MSP430PassConfig::addIRPasses() {
+  addPass(createAtomicExpandPass());
+
+  TargetPassConfig::addIRPasses();
+}
+
 bool MSP430PassConfig::addInstSelector() {
   // Install an instruction selector.
   addPass(createMSP430ISelDag(getMSP430TargetMachine(), getOptLevel()));
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
index e8f36bf50a1b0..de6de3214521e 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
@@ -854,6 +854,7 @@ NVPTXTargetLowering::NVPTXTargetLowering(const NVPTXTargetMachine &TM,
   computeRegisterProperties(STI.getRegisterInfo());
 
   setMinCmpXchgSizeInBits(32);
+  setMaxAtomicSizeInBitsSupported(64);
 }
 
 const char *NVPTXTargetLowering::getTargetNodeName(unsigned Opcode) const {
diff --git a/llvm/test/CodeGen/ARC/atomic-oversize.ll b/llvm/test/CodeGen/ARC/atomic-oversize.ll
new file mode 100644
index 0000000000000..678c1ae649c6a
--- /dev/null
+++ b/llvm/test/CodeGen/ARC/atomic-oversize.ll
@@ -0,0 +1,11 @@
+; RUN: llc -mtriple=arc < %s | FileCheck %s
+
+; Native atomics are unsupported, so all are oversize.
+define void @test(ptr %a) nounwind {
+; CHECK-LABEL: test:
+; CHECK: bl @__atomic_load_1
+; CHECK: bl @__atomic_store_1
+  %1 = load atomic i8, ptr %a seq_cst, align 16
+  store atomic i8 %1, ptr %a seq_cst, align 16
+  ret void
+}
diff --git a/llvm/test/CodeGen/BPF/atomic-oversize.ll b/llvm/test/CodeGen/BPF/atomic-oversize.ll
new file mode 100644
index 0000000000000..187f0964d4fb8
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/atomic-oversize.ll
@@ -0,0 +1,12 @@
+; RUN: llc -mtriple=bpf < %s | FileCheck %s
+; XFAIL: *
+; Doesn't currently build, with error 'only small returns supported'.
+
+define void @test(ptr %a) nounwind {
+; CHECK-LABEL: test:
+; CHECK: call __atomic_load_16
+; CHECK: call __atomic_store_16
+  %1 = load atomic i128, ptr %a monotonic, align 16
+  store atomic i128 %1, ptr %a monotonic, align 16
+  ret void
+}
diff --git a/llvm/test/CodeGen/Lanai/atomic-oversize.ll b/llvm/test/CodeGen/Lanai/atomic-oversize.ll
new file mode 100644
index 0000000000000..93307ac8184d0
--- /dev/null
+++ b/llvm/test/CodeGen/Lanai/atomic-oversize.ll
@@ -0,0 +1,11 @@
+; RUN: llc -mtriple=lanai < %s | FileCheck %s
+
+; Native atomics are unsupported, so all are oversize.
+define void @test(ptr %a) nounwind {
+; CHECK-LABEL: test:
+; CHECK: bt __atomic_load_1
+; CHECK: bt __atomic_store_1
+  %1 = load atomic i8, ptr %a monotonic, align 16
+  store atomic i8 %1, ptr %a monotonic, align 16
+  ret void
+}
diff --git a/llvm/test/CodeGen/MSP430/atomic-oversize.ll b/llvm/test/CodeGen/MSP430/atomic-oversize.ll
new file mode 100644
index 0000000000000..53b668ab25b56
--- /dev/null
+++ b/llvm/test/CodeGen/MSP430/atomic-oversize.ll
@@ -0,0 +1,11 @@
+; RUN: llc -mtriple=msp430 < %s | FileCheck %s
+
+; Native atomics are unsupported, so all are oversize.
+define void @test(ptr %a) nounwind {
+; CHECK-LABEL: test:
+; CHECK: call #__atomic_load_1
+; CHECK: call #__atomic_store_1
+  %1 = load atomic i8, ptr %a monotonic, align 16
+  store atomic i8 %1, ptr %a monotonic, align 16
+  ret void
+}
diff --git a/llvm/test/CodeGen/NVPTX/atomicrmw-expand.ll b/llvm/test/CodeGen/NVPTX/atomicrmw-expand.ll
index d4fd620592048..b65c281092dd7 100644
--- a/llvm/test/CodeGen/NVPTX/atomicrmw-expand.ll
+++ b/llvm/test/CodeGen/NVPTX/atomicrmw-expand.ll
@@ -140,26 +140,30 @@ entry:
   ret void
 }
 
-; TODO: We might still want to test other types, such as i128. Currently the
-; backend doesn't support them. Atomic expand only supports expansion to cas of
-; the same bitwidth, which means even after expansion, the back end still
-; doesn't support the instruction. Here we still put the tests. Remove the
-; comment once we have proper support, either from atomic expand or backend.
-
-; define void @bitwise_i128(ptr %0, i128 %1) {
-; entry:
-;   %2 = atomicrmw and ptr %0, i128 %1 monotonic, align 16
-;   %3 = atomicrmw or ptr %0, i128 %1 monotonic, align 16
-;   %4 = atomicrmw xor ptr %0, i128 %1 monotonic, align 16
-;   %5 = atomicrmw xchg ptr %0, i128 %1 monotonic, align 16
-;   ret void
-; }
+; CHECK-LABEL: bitwise_i128
+define void @bitwise_i128(ptr %0, i128 %1) {
+entry:
+  ; ALL: __atomic_fetch_and_16
+  %2 = atomicrmw and ptr %0, i128 %1 monotonic, align 16
+  ; ALL: __atomic_fetch_or_16
+  %3 = atomicrmw or ptr %0, i128 %1 monotonic, align 16
+  ; ALL: __atomic_fetch_xor_16
+  %4 = atomicrmw xor ptr %0, i128 %1 monotonic, align 16
+  ; ALL: __atomic_exchange_16
+  %5 = atomicrmw xchg ptr %0, i128 %1 monotonic, align 16
+  ret void
+}
 
-; define void @minmax_i128(ptr %0, i128 %1) {
-; entry:
-;   %2 = atomicrmw min ptr %0, i128 %1 monotonic, align 16
-;   %3 = atomicrmw max ptr %0, i128 %1 monotonic, align 16
-;   %4 = atomicrmw umin ptr %0, i128 %1 monotonic, align 16
-;   %5 = atomicrmw umax ptr %0, i128 %1 monotonic, align 16
-;   ret void
-; }
+; CHECK-LABEL: minmax_i128
+define void @minmax_i128(ptr %0, i128 %1) {
+entry:
+  ; ALL: __atomic_compare_exchange_16
+  %2 = atomicrmw min ptr %0, i128 %1 monotonic, align 16
+  ; ALL: __atomic_compare_exchange_16
+  %3 = atomicrmw max ptr %0, i128 %1 monotonic, align 16
+  ; ALL: __atomic_compare_exchange_16
+  %4 = atomicrmw umin ptr %0, i128 %1 monotonic, align 16
+  ; ALL: __atomic_compare_exchange_16
+  %5 = atomicrmw umax ptr %0, i128 %1 monotonic, align 16
+  ret void
+}