- Function *DMB = llvm::Intrinsic::getDeclaration(M, Intrinsic::arm_dmb);
- Constant *CDomain = Builder.getInt32(Domain);
- Builder.CreateCall(DMB, CDomain);
+
+ // First, if the target has no DMB, see what fallback we can use.
+ if (!Subtarget->hasDataBarrier()) {
+ // Some ARMv6 cpus can support data barriers with an mcr instruction.
+ // Thumb1 and pre-v6 ARM mode use a libcall instead and should never get
+ // here.
+ if (Subtarget->hasV6Ops() && !Subtarget->isThumb()) {
+ Function *MCR = llvm::Intrinsic::getDeclaration(M, Intrinsic::arm_mcr);
+ ArrayRef<Value*> args = {Builder.getInt32(15), Builder.getInt32(0),
+ Builder.getInt32(0), Builder.getInt32(7),
+ Builder.getInt32(10), Builder.getInt32(5)};
+ return Builder.CreateCall(MCR, args);
+ } else {
+ // Instead of using barriers, atomic accesses on these subtargets use
+ // libcalls.
+ llvm_unreachable("makeDMB on a target so old that it has no barriers");
+ }
+ } else {
+ Function *DMB = llvm::Intrinsic::getDeclaration(M, Intrinsic::arm_dmb);
+ // Only a full system barrier exists in the M-class architectures.
+ Domain = Subtarget->isMClass() ? ARM_MB::SY : Domain;
+ Constant *CDomain = Builder.getInt32(Domain);
+ return Builder.CreateCall(DMB, CDomain);
+ }