diff --git a/llvm/lib/Transforms/IPO/OpenMPOpt.cpp b/llvm/lib/Transforms/IPO/OpenMPOpt.cpp
--- a/llvm/lib/Transforms/IPO/OpenMPOpt.cpp
+++ b/llvm/lib/Transforms/IPO/OpenMPOpt.cpp
@@ -111,11 +111,47 @@
                       << " functions\n");
 
     Changed |= deduplicateRuntimeCalls();
+    Changed |= deleteParallelRegions();
 
     return Changed;
   }
 
 private:
+  /// Try to delete parallel regions if possible
+  bool deleteParallelRegions() {
+    const unsigned CallbackCalleeOperand = 2;
+
+    RuntimeFunctionInfo &RFI = RFIs[OMPRTL___kmpc_fork_call];
+    if (!RFI.Declaration)
+      return false;
+
+    bool Changed = false;
+    auto DeleteCallCB = [&](Use &U, Function &) {
+      CallInst *CI = getCallIfRegularCall(U);
+      if (!CI)
+        return false;
+      auto *Fn = dyn_cast<Function>(
+          CI->getArgOperand(CallbackCalleeOperand)->stripPointerCasts());
+      if (!Fn)
+        return false;
+      if (!Fn->onlyReadsMemory())
+        return false;
+      if (!Fn->hasFnAttribute(Attribute::WillReturn))
+        return false;
+
+      LLVM_DEBUG(dbgs() << TAG << "Delete read-only parallel region in "
+                        << CI->getCaller()->getName() << "\n");
+      CGUpdater.removeCallSite(*CI);
+      CI->eraseFromParent();
+      Changed = true;
+      return true;
+    };
+
+    RFI.foreachUse(DeleteCallCB);
+
+    return Changed;
+  }
+
   /// Try to eliminiate runtime calls by reusing existing ones.
   bool deduplicateRuntimeCalls() {
     bool Changed = false;
diff --git a/llvm/test/Transforms/OpenMP/parallel_deletion.ll b/llvm/test/Transforms/OpenMP/parallel_deletion.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/OpenMP/parallel_deletion.ll
@@ -0,0 +1,309 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -attributor -openmpopt -attributor-disable=false < %s | FileCheck %s
+; RUN: opt -S -passes='attributor,cgscc(openmpopt)' -attributor-disable=false < %s | FileCheck %s
+;
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+%struct.ident_t = type { i32, i32, i32, i32, i8* }
+
+@.str = private unnamed_addr constant [23 x i8] c";unknown;unknown;0;0;;\00", align 1
+@0 = private unnamed_addr global %struct.ident_t { i32 0, i32 2, i32 0, i32 0, i8* getelementptr inbounds ([23 x i8], [23 x i8]* @.str, i32 0, i32 0) }, align 8
+@1 = private unnamed_addr global %struct.ident_t { i32 0, i32 322, i32 0, i32 0, i8* getelementptr inbounds ([23 x i8], [23 x i8]* @.str, i32 0, i32 0) }, align 8
+@.gomp_critical_user_.reduction.var = common global [8 x i32] zeroinitializer
+@2 = private unnamed_addr global %struct.ident_t { i32 0, i32 18, i32 0, i32 0, i8* getelementptr inbounds ([23 x i8], [23 x i8]* @.str, i32 0, i32 0) }, align 8
+
+;    void delete_parallel_0(void) {
+;    #pragma omp parallel
+;      { unknown_willreturn(); }
+;    #pragma omp parallel
+;      { readonly_willreturn(); }
+;    #pragma omp parallel
+;      { readnone_willreturn(); }
+;    #pragma omp parallel
+;      {}
+;    }
+;
+; We delete all but the first of the parallel regions in this test.
+define void @delete_parallel_0() {
+; CHECK-LABEL: define {{[^@]+}}@delete_parallel_0()
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 0, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*)* @.omp_outlined.willreturn to void (i32*, i32*, ...)*))
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined.willreturn to void (i32*, i32*, ...)*))
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined.willreturn.0 to void (i32*, i32*, ...)*))
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined.willreturn.1 to void (i32*, i32*, ...)*))
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined.willreturn.2 to void (i32*, i32*, ...)*))
+  ret void
+}
+
+define internal void @.omp_outlined.willreturn(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+entry:
+  call void @unknown() willreturn
+  ret void
+}
+
+define internal void @.omp_outlined.willreturn.0(i32* noalias %.global_tid., i32* noalias %.bound_tid.) willreturn {
+entry:
+  call void @readonly()
+  ret void
+}
+
+define internal void @.omp_outlined.willreturn.1(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+entry:
+  call void @readnone() willreturn
+  ret void
+}
+
+define internal void @.omp_outlined.willreturn.2(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+entry:
+  ret void
+}
+
+;    void delete_parallel_1(void) {
+;    #pragma omp parallel
+;      { unknown(); }
+;    #pragma omp parallel
+;      { readonly(); }
+;    #pragma omp parallel
+;      { readnone(); }
+;    #pragma omp parallel
+;      {}
+;    }
+;
+; We delete only the last parallel regions in this test because the others might not return.
+define void @delete_parallel_1() {
+; CHECK-LABEL: define {{[^@]+}}@delete_parallel_1()
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 0, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*)* @.omp_outlined. to void (i32*, i32*, ...)*))
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 0, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*)* @.omp_outlined..0 to void (i32*, i32*, ...)*))
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 0, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*)* @.omp_outlined..1 to void (i32*, i32*, ...)*))
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined. to void (i32*, i32*, ...)*))
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined..0 to void (i32*, i32*, ...)*))
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined..1 to void (i32*, i32*, ...)*))
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 0, void (i32*, i32*, ...)* bitcast (void (i32*, i32*)* @.omp_outlined..2 to void (i32*, i32*, ...)*))
+  ret void
+}
+
+define internal void @.omp_outlined.(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+entry:
+  call void @unknown()
+  ret void
+}
+
+define internal void @.omp_outlined..0(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+entry:
+  call void @readonly()
+  ret void
+}
+
+define internal void @.omp_outlined..1(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+entry:
+  call void @readnone()
+  ret void
+}
+
+define internal void @.omp_outlined..2(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+entry:
+  ret void
+}
+
+;    void delete_parallel_2(void) {
+;      int a = 0;
+;    #pragma omp parallel
+;      {
+;        if (omp_get_thread_num() == 0)
+;          ++a;
+;      }
+;    #pragma omp parallel
+;      {
+;    #pragma omp master
+;        ++a;
+;      }
+;    #pragma omp parallel
+;      {
+;    #pragma omp single
+;        ++a;
+;      }
+;    #pragma omp parallel reduction(+: a)
+;      {
+;        ++a;
+;      }
+;    }
+;
+; FIXME: We do not realize that `a` is dead and all accesses to it can be removed
+;        making the parallel regions readonly and deletable.
+define void @delete_parallel_2() {
+; CHECK-LABEL: define {{[^@]+}}@delete_parallel_2()
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[TMP:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull align 4 dereferenceable(4) [[TMP]])
+; CHECK-NEXT:    store i32 0, i32* [[A]], align 4
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 1, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*, i32*)* @.omp_outlined..3 to void (i32*, i32*, ...)*), i32* nocapture nofree nonnull align 4 dereferenceable(4) [[A]])
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 1, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*, i32*)* @.omp_outlined..4 to void (i32*, i32*, ...)*), i32* nocapture nonnull align 4 dereferenceable(4) [[A]])
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 1, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*, i32*)* @.omp_outlined..5 to void (i32*, i32*, ...)*), i32* nocapture nonnull align 4 dereferenceable(4) [[A]])
+; CHECK-NEXT:    call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull align 8 dereferenceable(24) @0, i32 1, void (i32*, i32*, ...)* nonnull bitcast (void (i32*, i32*, i32*)* @.omp_outlined..6 to void (i32*, i32*, ...)*), i32* nocapture nonnull align 4 dereferenceable(4) [[A]])
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i32* [[A]] to i8*
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  %a = alloca i32, align 4
+  %tmp = bitcast i32* %a to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %tmp)
+  store i32 0, i32* %a, align 4
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 1, void (i32*, i32*, ...)* bitcast (void (i32*, i32*, i32*)* @.omp_outlined..3 to void (i32*, i32*, ...)*), i32* nonnull %a)
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 1, void (i32*, i32*, ...)* bitcast (void (i32*, i32*, i32*)* @.omp_outlined..4 to void (i32*, i32*, ...)*), i32* nonnull %a)
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 1, void (i32*, i32*, ...)* bitcast (void (i32*, i32*, i32*)* @.omp_outlined..5 to void (i32*, i32*, ...)*), i32* nonnull %a)
+  call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 1, void (i32*, i32*, ...)* bitcast (void (i32*, i32*, i32*)* @.omp_outlined..6 to void (i32*, i32*, ...)*), i32* nonnull %a)
+  %tmp1 = bitcast i32* %a to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %tmp1)
+  ret void
+}
+
+define internal void @.omp_outlined..3(i32* noalias %.global_tid., i32* noalias %.bound_tid., i32* dereferenceable(4) %a) {
+entry:
+  %call = call i32 @omp_get_thread_num()
+  %cmp = icmp eq i32 %call, 0
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  %tmp = load i32, i32* %a, align 4
+  %inc = add nsw i32 %tmp, 1
+  store i32 %inc, i32* %a, align 4
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  ret void
+}
+
+define internal void @.omp_outlined..4(i32* noalias %.global_tid., i32* noalias %.bound_tid., i32* dereferenceable(4) %a) {
+entry:
+  %tmp = load i32, i32* %.global_tid., align 4
+  %tmp1 = call i32 @__kmpc_master(%struct.ident_t* nonnull @0, i32 %tmp)
+  %tmp2 = icmp eq i32 %tmp1, 0
+  br i1 %tmp2, label %omp_if.end, label %omp_if.then
+
+omp_if.then:                                      ; preds = %entry
+  %tmp3 = load i32, i32* %a, align 4
+  %inc = add nsw i32 %tmp3, 1
+  store i32 %inc, i32* %a, align 4
+  call void @__kmpc_end_master(%struct.ident_t* nonnull @0, i32 %tmp)
+  br label %omp_if.end
+
+omp_if.end:                                       ; preds = %entry, %omp_if.then
+  ret void
+}
+
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture)
+
+declare i32 @omp_get_thread_num() inaccessiblememonly nofree nosync nounwind readonly
+
+declare i32 @__kmpc_master(%struct.ident_t*, i32)
+
+declare void @__kmpc_end_master(%struct.ident_t*, i32)
+
+define internal void @.omp_outlined..5(i32* noalias %.global_tid., i32* noalias %.bound_tid., i32* dereferenceable(4) %a) {
+entry:
+  %omp_global_thread_num = call i32 @__kmpc_global_thread_num(%struct.ident_t* nonnull @0)
+  %tmp = load i32, i32* %.global_tid., align 4
+  %tmp1 = call i32 @__kmpc_single(%struct.ident_t* nonnull @0, i32 %tmp)
+  %tmp2 = icmp eq i32 %tmp1, 0
+  br i1 %tmp2, label %omp_if.end, label %omp_if.then
+
+omp_if.then:                                      ; preds = %entry
+  %tmp3 = load i32, i32* %a, align 4
+  %inc = add nsw i32 %tmp3, 1
+  store i32 %inc, i32* %a, align 4
+  call void @__kmpc_end_single(%struct.ident_t* nonnull @0, i32 %tmp)
+  br label %omp_if.end
+
+omp_if.end:                                       ; preds = %entry, %omp_if.then
+  call void @__kmpc_barrier(%struct.ident_t* nonnull @1, i32 %omp_global_thread_num) #6
+  ret void
+}
+
+define internal void @.omp_outlined..6(i32* noalias %.global_tid., i32* noalias %.bound_tid., i32* dereferenceable(4) %a) {
+entry:
+  %a1 = alloca i32, align 4
+  %.omp.reduction.red_list = alloca [1 x i8*], align 8
+  %tmp = bitcast i32* %a1 to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %tmp)
+  store i32 1, i32* %a1, align 4
+  %tmp1 = bitcast [1 x i8*]* %.omp.reduction.red_list to i32**
+  store i32* %a1, i32** %tmp1, align 8
+  %tmp2 = load i32, i32* %.global_tid., align 4
+  %tmp3 = bitcast [1 x i8*]* %.omp.reduction.red_list to i8*
+  %tmp4 = call i32 @__kmpc_reduce_nowait(%struct.ident_t* nonnull @2, i32 %tmp2, i32 1, i64 8, i8* nonnull %tmp3, void (i8*, i8*)* nonnull @.omp.reduction.reduction_func, [8 x i32]* nonnull @.gomp_critical_user_.reduction.var)
+  switch i32 %tmp4, label %.omp.reduction.default [
+    i32 1, label %.omp.reduction.case1
+    i32 2, label %.omp.reduction.case2
+  ]
+
+.omp.reduction.case1:                             ; preds = %entry
+  %tmp5 = load i32, i32* %a, align 4
+  %tmp6 = load i32, i32* %a1, align 4
+  %add = add nsw i32 %tmp5, %tmp6
+  store i32 %add, i32* %a, align 4
+  call void @__kmpc_end_reduce_nowait(%struct.ident_t* nonnull @2, i32 %tmp2, [8 x i32]* nonnull @.gomp_critical_user_.reduction.var)
+  br label %.omp.reduction.default
+
+.omp.reduction.case2:                             ; preds = %entry
+  %tmp7 = load i32, i32* %a1, align 4
+  %tmp8 = atomicrmw add i32* %a, i32 %tmp7 monotonic
+  br label %.omp.reduction.default
+
+.omp.reduction.default:                           ; preds = %.omp.reduction.case2, %.omp.reduction.case1, %entry
+  %tmp9 = bitcast i32* %a1 to i8*
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %tmp9)
+  ret void
+}
+
+define internal void @.omp.reduction.reduction_func(i8* %arg, i8* %arg1) {
+entry:
+  %tmp = bitcast i8* %arg1 to i32**
+  %tmp2 = load i32*, i32** %tmp, align 8
+  %tmp3 = bitcast i8* %arg to i32**
+  %tmp4 = load i32*, i32** %tmp3, align 8
+  %tmp5 = load i32, i32* %tmp4, align 4
+  %tmp6 = load i32, i32* %tmp2, align 4
+  %add = add nsw i32 %tmp5, %tmp6
+  store i32 %add, i32* %tmp4, align 4
+  ret void
+}
+
+declare i32 @__kmpc_single(%struct.ident_t*, i32)
+
+declare void @__kmpc_end_single(%struct.ident_t*, i32)
+
+declare void @__kmpc_barrier(%struct.ident_t*, i32)
+
+declare i32 @__kmpc_global_thread_num(%struct.ident_t*) nofree nosync nounwind readonly
+
+declare i32 @__kmpc_reduce_nowait(%struct.ident_t*, i32, i32, i64, i8*, void (i8*, i8*)*, [8 x i32]*)
+
+declare void @__kmpc_end_reduce_nowait(%struct.ident_t*, i32, [8 x i32]*)
+
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture)
+
+declare !callback !2 void @__kmpc_fork_call(%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...)
+
+declare void @unknown()
+
+declare void @readonly() readonly
+
+declare void @readnone() readnone
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{!"clang"}
+!2 = !{!3}
+!3 = !{i64 2, i64 -1, i64 -1, i1 true}
+!4 = !{!5, !5, i64 0}
+!5 = !{!"int", !6, i64 0}
+!6 = !{!"omnipotent char", !7, i64 0}
+!7 = !{!"Simple C/C++ TBAA"}