Index: include/llvm/CodeGen/MachineInstr.h
===================================================================
--- include/llvm/CodeGen/MachineInstr.h
+++ include/llvm/CodeGen/MachineInstr.h
@@ -537,6 +537,8 @@
   /// Convergent instructions can not be made control-dependent on any
   /// additional values.
   bool isConvergent(QueryType Type = AnyInBundle) const {
+    // TODO: Convergent calls should also be convergent.  (That is, convergence
+    // depends on the call itself, not just on the instruction.)
     return hasProperty(MCID::Convergent, Type);
   }
 
Index: lib/CodeGen/TailDuplication.cpp
===================================================================
--- lib/CodeGen/TailDuplication.cpp
+++ lib/CodeGen/TailDuplication.cpp
@@ -588,6 +588,11 @@
     if (MI.isNotDuplicable())
       return false;
 
+    // Convergent instructions can be duplicated only if doing so doesn't add
+    // new control dependencies, which is what we're going to do here.
+    if (MI.isConvergent())
+      return false;
+
     // Do not duplicate 'return' instructions if this is a pre-regalloc run.
     // A return may expand into a lot more instructions (e.g. reload of callee
     // saved registers) after PEI.
Index: test/CodeGen/NVPTX/TailDuplication-convergent.ll
===================================================================
--- /dev/null
+++ test/CodeGen/NVPTX/TailDuplication-convergent.ll
@@ -0,0 +1,45 @@
+; RUN: llc -O2 -tail-dup-size=100 -enable-tail-merge=0 < %s | FileCheck %s
+target triple = "nvptx64-nvidia-cuda"
+
+declare void @foo()
+declare void @llvm.cuda.syncthreads()
+
+; syncthreads shouldn't be duplicated.
+; CHECK: .func call_syncthreads
+; CHECK: bar.sync
+; CHECK-NOT: bar.sync
+define void @call_syncthreads(i32* %a, i32* %b, i1 %cond, i1 %cond2) nounwind {
+  br i1 %cond, label %L1, label %L2
+  br i1 %cond2, label %Ret, label %L1
+Ret:
+  ret void
+L1:
+  store i32 0, i32* %a
+  br label %L42
+L2:
+  store i32 1, i32* %a
+  br label %L42
+L42:
+  call void @llvm.cuda.syncthreads()
+  br label %Ret
+}
+
+; Check that call_syncthreads really does trigger tail duplication.
+; CHECK: .func call_foo
+; CHECK: call
+; CHECK: call
+define void @call_foo(i32* %a, i32* %b, i1 %cond, i1 %cond2) nounwind {
+  br i1 %cond, label %L1, label %L2
+  br i1 %cond2, label %Ret, label %L1
+Ret:
+  ret void
+L1:
+  store i32 0, i32* %a
+  br label %L42
+L2:
+  store i32 1, i32* %a
+  br label %L42
+L42:
+  call void @foo()
+  br label %Ret
+}