Index: llvm/trunk/include/llvm/IR/IntrinsicsAArch64.td
===================================================================
--- llvm/trunk/include/llvm/IR/IntrinsicsAArch64.td
+++ llvm/trunk/include/llvm/IR/IntrinsicsAArch64.td
@@ -43,6 +43,13 @@
 def int_aarch64_rbit : Intrinsic<[llvm_anyint_ty], [LLVMMatchType<0>],
                                  [IntrNoMem]>;
 
+//===----------------------------------------------------------------------===//
+// Data Barrier Instructions
+
+def int_aarch64_dmb : GCCBuiltin<"__builtin_arm_dmb">, Intrinsic<[], [llvm_i32_ty]>;
+def int_aarch64_dsb : GCCBuiltin<"__builtin_arm_dsb">, Intrinsic<[], [llvm_i32_ty]>;
+def int_aarch64_isb : GCCBuiltin<"__builtin_arm_isb">, Intrinsic<[], [llvm_i32_ty]>;
+
 }
 
 //===----------------------------------------------------------------------===//
Index: llvm/trunk/lib/Target/AArch64/AArch64InstrFormats.td
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64InstrFormats.td
+++ llvm/trunk/lib/Target/AArch64/AArch64InstrFormats.td
@@ -539,6 +539,11 @@
   let ParserMatchClass = Imm0_7Operand;
 }
 
+// imm32_0_15 predicate - True if the 32-bit immediate is in the range [0,15]
+def imm32_0_15 : Operand<i32>, ImmLeaf<i32, [{
+  return ((uint32_t)Imm) < 16;
+}]>;
+
 // An arithmetic shifter operand:
 //  {7-6} - shift type: 00 = lsl, 01 = lsr, 10 = asr
 //  {5-0} - imm6
@@ -821,8 +826,9 @@
   let PrintMethod = "printBarrierOption";
   let ParserMatchClass = BarrierAsmOperand;
 }
-class CRmSystemI<Operand crmtype, bits<3> opc, string asm>
-    : SimpleSystemI<0, (ins crmtype:$CRm), asm, "\t$CRm">,
+class CRmSystemI<Operand crmtype, bits<3> opc, string asm,
+                 list<dag> pattern = []>
+    : SimpleSystemI<0, (ins crmtype:$CRm), asm, "\t$CRm", pattern>,
       Sched<[WriteBarrier]> {
   bits<4> CRm;
   let Inst{20-12} = 0b000110011;
Index: llvm/trunk/lib/Target/AArch64/AArch64InstrInfo.td
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64InstrInfo.td
+++ llvm/trunk/lib/Target/AArch64/AArch64InstrInfo.td
@@ -331,13 +331,23 @@
 def : InstAlias<"sev",  (HINT 0b100)>;
 def : InstAlias<"sevl", (HINT 0b101)>;
 
-  // As far as LLVM is concerned this writes to the system's exclusive monitors.
+// As far as LLVM is concerned this writes to the system's exclusive monitors.
 let mayLoad = 1, mayStore = 1 in
 def CLREX : CRmSystemI<imm0_15, 0b010, "clrex">;
 
-def DMB   : CRmSystemI<barrier_op, 0b101, "dmb">;
-def DSB   : CRmSystemI<barrier_op, 0b100, "dsb">;
-def ISB   : CRmSystemI<barrier_op, 0b110, "isb">;
+// NOTE: ideally, this would have mayStore = 0, mayLoad = 0, but we cannot
+// model patterns with sufficiently fine granularity.
+let mayLoad = ?, mayStore = ? in {
+def DMB   : CRmSystemI<barrier_op, 0b101, "dmb",
+                       [(int_aarch64_dmb (i32 imm32_0_15:$CRm))]>;
+
+def DSB   : CRmSystemI<barrier_op, 0b100, "dsb",
+                       [(int_aarch64_dsb (i32 imm32_0_15:$CRm))]>;
+
+def ISB   : CRmSystemI<barrier_op, 0b110, "isb",
+                       [(int_aarch64_isb (i32 imm32_0_15:$CRm))]>;
+}
+
 def : InstAlias<"clrex", (CLREX 0xf)>;
 def : InstAlias<"isb", (ISB 0xf)>;
 
Index: llvm/trunk/test/CodeGen/AArch64/intrinsics-memory-barrier.ll
===================================================================
--- llvm/trunk/test/CodeGen/AArch64/intrinsics-memory-barrier.ll
+++ llvm/trunk/test/CodeGen/AArch64/intrinsics-memory-barrier.ll
@@ -0,0 +1,57 @@
+; RUN: llc < %s -mtriple=aarch64-eabi -O=3 | FileCheck %s
+
+define void @test() {
+  ; CHECK: dmb sy
+  call void @llvm.aarch64.dmb(i32 15)
+  ; CHECK: dmb osh
+  call void @llvm.aarch64.dmb(i32 3)
+  ; CHECK: dsb sy
+  call void @llvm.aarch64.dsb(i32 15)
+  ; CHECK: dsb ishld
+  call void @llvm.aarch64.dsb(i32 9)
+  ; CHECK: isb
+  call void @llvm.aarch64.isb(i32 15)
+  ret void
+}
+
+; Important point is that the compiler should not reorder memory access
+; instructions around DMB.
+; Failure to do so, two STRs will collapse into one STP.
+define void @test_dmb_reordering(i32 %a, i32 %b, i32* %d) {
+  store i32 %a, i32* %d              ; CHECK: str {{w[0-9]+}}, [{{x[0-9]+}}]
+
+  call void @llvm.aarch64.dmb(i32 15); CHECK: dmb sy
+
+  %d1 = getelementptr i32* %d, i64 1
+  store i32 %b, i32* %d1             ; CHECK: str {{w[0-9]+}}, [{{x[0-9]+}}, #4]
+
+  ret void
+}
+
+; Similarly for DSB.
+define void @test_dsb_reordering(i32 %a, i32 %b, i32* %d) {
+  store i32 %a, i32* %d              ; CHECK: str {{w[0-9]+}}, [{{x[0-9]+}}]
+
+  call void @llvm.aarch64.dsb(i32 15); CHECK: dsb sy
+
+  %d1 = getelementptr i32* %d, i64 1
+  store i32 %b, i32* %d1             ; CHECK: str {{w[0-9]+}}, [{{x[0-9]+}}, #4]
+
+  ret void
+}
+
+; And ISB.
+define void @test_isb_reordering(i32 %a, i32 %b, i32* %d) {
+  store i32 %a, i32* %d              ; CHECK: str {{w[0-9]+}}, [{{x[0-9]+}}]
+
+  call void @llvm.aarch64.isb(i32 15); CHECK: isb
+
+  %d1 = getelementptr i32* %d, i64 1
+  store i32 %b, i32* %d1             ; CHECK: str {{w[0-9]+}}, [{{x[0-9]+}}, #4]
+
+  ret void
+}
+
+declare void @llvm.aarch64.dmb(i32)
+declare void @llvm.aarch64.dsb(i32)
+declare void @llvm.aarch64.isb(i32)