Index: llvm/test/tools/llvm-reduce/reduce-atomic-ordering.ll
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-reduce/reduce-atomic-ordering.ll
@@ -0,0 +1,82 @@
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=atomic-ordering --test FileCheck --test-arg --check-prefixes=INTERESTING,CHECK --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck -check-prefixes=RESULT,CHECK %s < %t
+
+; CHECK-LABEL: @load_atomic_keep(
+; INTERESTING: seq_cst
+; RESULT: %op = load atomic i32, ptr %ptr syncscope("agent") seq_cst, align 4
+define i32 @load_atomic_keep(ptr %ptr) {
+  %op = load atomic i32, ptr %ptr syncscope("agent") seq_cst, align 4
+  ret i32 %op
+}
+
+; CHECK-LABEL: @load_atomic_drop(
+; INTERESTING: load
+; RESULT: %op = load i32, ptr %ptr, align 4
+define i32 @load_atomic_drop(ptr %ptr) {
+  %op = load atomic i32, ptr %ptr syncscope("agent") seq_cst, align 4
+  ret i32 %op
+}
+
+; CHECK-LABEL: @store_atomic_keep(
+; INTERESTING: syncscope("agent")
+; RESULT: store atomic i32 0, ptr %ptr syncscope("agent") seq_cst, align 4
+define void @store_atomic_keep(ptr %ptr) {
+  store atomic i32 0, ptr %ptr syncscope("agent") seq_cst, align 4
+  ret void
+}
+
+; CHECK-LABEL: @store_atomic_drop(
+; INTERESTING: store
+; RESULT: store i32 0, ptr %ptr, align 4
+define void @store_atomic_drop(ptr %ptr) {
+  store atomic i32 0, ptr %ptr syncscope("agent") seq_cst, align 4
+  ret void
+}
+
+; CHECK-LABEL: @atomicrmw_atomic_seq_cst_keep(
+; INTERESTING: seq_cst
+; RESULT: %val = atomicrmw add ptr %ptr, i32 3 syncscope("agent") seq_cst, align 4
+define i32 @atomicrmw_atomic_seq_cst_keep(ptr %ptr) {
+  %val = atomicrmw add ptr %ptr, i32 3 syncscope("agent") seq_cst, align 4
+  ret i32 %val
+}
+
+; CHECK-LABEL: @atomicrmw_atomic_seq_cst_drop(
+; INTERESTING: atomicrmw
+; RESULT: %val = atomicrmw add ptr %ptr, i32 3 monotonic, align 4
+define i32 @atomicrmw_atomic_seq_cst_drop(ptr %ptr) {
+  %val = atomicrmw add ptr %ptr, i32 3 seq_cst
+  ret i32 %val
+}
+
+; CHECK-LABEL: @cmpxchg_atomic_seq_cst_seq_cst_keep(
+; INTERESTING: seq_cst seq_cst
+; RESULT: %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") seq_cst seq_cst, align 4
+define { i32, i1 } @cmpxchg_atomic_seq_cst_seq_cst_keep(ptr %ptr, i32 %old, i32 %in) {
+  %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") seq_cst seq_cst
+  ret { i32, i1 } %val
+}
+
+; CHECK-LABEL: @cmpxchg_seq_cst_seq_cst_keep_left(
+; INTERESTING: syncscope("agent") seq_cst
+; RESULT: %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") seq_cst monotonic, align 4
+define { i32, i1 } @cmpxchg_seq_cst_seq_cst_keep_left(ptr %ptr, i32 %old, i32 %in) {
+  %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") seq_cst seq_cst
+  ret { i32, i1 } %val
+}
+
+; CHECK-LABEL: @cmpxchg_seq_cst_seq_cst_keep_right(
+; INTERESTING: seq_cst, align 4
+; RESULT: %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") monotonic seq_cst, align 4
+define { i32, i1 } @cmpxchg_seq_cst_seq_cst_keep_right(ptr %ptr, i32 %old, i32 %in) {
+  %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") seq_cst seq_cst, align 4
+  ret { i32, i1 } %val
+}
+
+; CHECK-LABEL: @cmpxchg_seq_cst_seq_cst_drop(
+; INTERESTING: = cmpxchg ptr
+; RESULT: %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") monotonic monotonic, align 4
+define { i32, i1 } @cmpxchg_seq_cst_seq_cst_drop(ptr %ptr, i32 %old, i32 %in) {
+  %val = cmpxchg ptr %ptr, i32 %old, i32 %in syncscope("agent") seq_cst seq_cst
+  ret { i32, i1 } %val
+}
Index: llvm/tools/llvm-reduce/DeltaManager.cpp
===================================================================
--- llvm/tools/llvm-reduce/DeltaManager.cpp
+++ llvm/tools/llvm-reduce/DeltaManager.cpp
@@ -97,6 +97,7 @@
     DELTA_PASS("module-data", reduceModuleDataDeltaPass)                       \
     DELTA_PASS("opcodes", reduceOpcodesDeltaPass)                              \
     DELTA_PASS("volatile", reduceVolatileInstructionsDeltaPass)                \
+    DELTA_PASS("atomic-ordering", reduceAtomicOrderingDeltaPass)               \
     DELTA_PASS("syncscopes", reduceAtomicSyncScopesDeltaPass)                  \
     DELTA_PASS("instruction-flags", reduceInstructionFlagsDeltaPass)           \
 } while (false)
Index: llvm/tools/llvm-reduce/deltas/ReduceMemoryOperations.h
===================================================================
--- llvm/tools/llvm-reduce/deltas/ReduceMemoryOperations.h
+++ llvm/tools/llvm-reduce/deltas/ReduceMemoryOperations.h
@@ -14,6 +14,7 @@
 namespace llvm {
 void reduceVolatileInstructionsDeltaPass(TestRunner &Test);
 void reduceAtomicSyncScopesDeltaPass(TestRunner &Test);
+void reduceAtomicOrderingDeltaPass(TestRunner &Test);
 } // namespace llvm
 
 #endif
Index: llvm/tools/llvm-reduce/deltas/ReduceMemoryOperations.cpp
===================================================================
--- llvm/tools/llvm-reduce/deltas/ReduceMemoryOperations.cpp
+++ llvm/tools/llvm-reduce/deltas/ReduceMemoryOperations.cpp
@@ -73,3 +73,35 @@
   runDeltaPass(Test, reduceAtomicSyncScopesInModule,
                "Reducing Atomic Sync Scopes");
 }
+
+// TODO: Might be helpful to incrementally relax orders
+static void reduceAtomicOrderingInFunction(Oracle &O, Function &F) {
+  for (Instruction &I : instructions(F)) {
+    if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
+      if (LI->getOrdering() != AtomicOrdering::NotAtomic && !O.shouldKeep())
+        LI->setAtomic(AtomicOrdering::NotAtomic);
+    } else if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
+      if (SI->getOrdering() != AtomicOrdering::NotAtomic && !O.shouldKeep())
+        SI->setAtomic(AtomicOrdering::NotAtomic);
+    } else if (AtomicRMWInst *RMW = dyn_cast<AtomicRMWInst>(&I)) {
+      if (RMW->getOrdering() != AtomicOrdering::Monotonic && !O.shouldKeep())
+        RMW->setOrdering(AtomicOrdering::Monotonic);
+    } else if (AtomicCmpXchgInst *CmpXChg = dyn_cast<AtomicCmpXchgInst>(&I)) {
+      if (CmpXChg->getSuccessOrdering() != AtomicOrdering::Monotonic &&
+          !O.shouldKeep())
+        CmpXChg->setSuccessOrdering(AtomicOrdering::Monotonic);
+      if (CmpXChg->getFailureOrdering() != AtomicOrdering::Monotonic &&
+          !O.shouldKeep())
+        CmpXChg->setFailureOrdering(AtomicOrdering::Monotonic);
+    }
+  }
+}
+
+static void reduceAtomicOrderingInModule(Oracle &O, Module &Mod) {
+  for (Function &F : Mod)
+    reduceAtomicOrderingInFunction(O, F);
+}
+
+void llvm::reduceAtomicOrderingDeltaPass(TestRunner &Test) {
+  runDeltaPass(Test, reduceAtomicOrderingInModule, "Reducing Atomic Odering");
+}