diff --git a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -59,6 +59,20 @@
              "simplifications still taking place"),
     cl::init(1.5));
 
+#ifndef NDEBUG
+/// Return whether IP1 and IP2 are ambiguous, i.e. that inserting instructions
+/// at position IP1 may change the meaning of IP2 or vice-versa. This is because
+/// an InsertPoint stores the instruction before something is inserted. For
+/// instance, if both point to the same instruction, two IRBuilders alternating
+/// creating instruction will cause the instructions to be interleaved.
+static bool isConflictIP(IRBuilder<>::InsertPoint IP1,
+                         IRBuilder<>::InsertPoint IP2) {
+  if (!IP1.isSet() || !IP2.isSet())
+    return false;
+  return IP1.getBlock() == IP2.getBlock() && IP1.getPoint() == IP2.getPoint();
+}
+#endif
+
 void OpenMPIRBuilder::addAttributes(omp::RuntimeFunction FnID, Function &Fn) {
   LLVMContext &Ctx = Fn.getContext();
 
@@ -525,6 +539,8 @@
     BodyGenCallbackTy BodyGenCB, PrivatizeCallbackTy PrivCB,
     FinalizeCallbackTy FiniCB, Value *IfCondition, Value *NumThreads,
     omp::ProcBindKind ProcBind, bool IsCancellable) {
+  assert(!isConflictIP(Loc.IP, OuterAllocaIP) && "IPs must not me ambiguous");
+
   if (!updateToLocation(Loc))
     return Loc.IP;
 
diff --git a/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp b/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp
--- a/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp
+++ b/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp
@@ -483,6 +483,9 @@
   F->setName("func");
   IRBuilder<> Builder(BB);
 
+  BasicBlock *EnterBB = BasicBlock::Create(Ctx, "parallel.enter", F);
+  Builder.CreateBr(EnterBB);
+  Builder.SetInsertPoint(EnterBB);
   OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
 
   AllocaInst *PrivAI = nullptr;
@@ -589,6 +592,9 @@
   F->setName("func");
   IRBuilder<> Builder(BB);
 
+  BasicBlock *EnterBB = BasicBlock::Create(Ctx, "parallel.enter", F);
+  Builder.CreateBr(EnterBB);
+  Builder.SetInsertPoint(EnterBB);
   OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
 
   unsigned NumInnerBodiesGenerated = 0;
@@ -682,6 +688,9 @@
   F->setName("func");
   IRBuilder<> Builder(BB);
 
+  BasicBlock *EnterBB = BasicBlock::Create(Ctx, "parallel.enter", F);
+  Builder.CreateBr(EnterBB);
+  Builder.SetInsertPoint(EnterBB);
   OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
 
   unsigned NumInnerBodiesGenerated = 0;
@@ -790,6 +799,9 @@
   F->setName("func");
   IRBuilder<> Builder(BB);
 
+  BasicBlock *EnterBB = BasicBlock::Create(Ctx, "parallel.enter", F);
+  Builder.CreateBr(EnterBB);
+  Builder.SetInsertPoint(EnterBB);
   OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
 
   AllocaInst *PrivAI = nullptr;
@@ -913,6 +925,9 @@
   F->setName("func");
   IRBuilder<> Builder(BB);
 
+  BasicBlock *EnterBB = BasicBlock::Create(Ctx, "parallel.enter", F);
+  Builder.CreateBr(EnterBB);
+  Builder.SetInsertPoint(EnterBB);
   OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
 
   unsigned NumBodiesGenerated = 0;
@@ -3075,6 +3090,10 @@
   OMPBuilder.initialize();
   F->setName("func");
   IRBuilder<> Builder(BB);
+
+  BasicBlock *EnterBB = BasicBlock::Create(Ctx, "parallel.enter", F);
+  Builder.CreateBr(EnterBB);
+  Builder.SetInsertPoint(EnterBB);
   OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
 
   // Create variables to be reduced.
@@ -3312,6 +3331,10 @@
   OMPBuilder.initialize();
   F->setName("func");
   IRBuilder<> Builder(BB);
+
+  BasicBlock *EnterBB = BasicBlock::Create(Ctx, "parallel.enter", F);
+  Builder.CreateBr(EnterBB);
+  Builder.SetInsertPoint(EnterBB);
   OpenMPIRBuilder::LocationDescription Loc({Builder.saveIP(), DL});
 
   // Create variables to be reduced.