[OpenMP] Prevent AMDGPU from overriding visibility on DT_nohost variables

Summary:
There's some logic in the AMDGPU target that manually resets the
requested visibility of certain variables. This was triggering when we
set a constant variable in OpenMP. However, we shouldn't do this for
OpenMP when the variable has the `nohost` type. That implies that the
variable is not visible to the host and therefore does not need to be
visible, so we should respect the original value of it.

Author: jhuber6

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1390,6 +1390,19 @@ void CodeGenModule::setGlobalVisibility(llvm::GlobalValue *GV,
   }
   if (!D)
     return;
+
+  // OpenMP declare target variables must be visible to the host so they can
+  // be registered. We require protected visibility unless the variable has
+  // the DT_nohost modifier and does not need to be registered.
+  if (Context.getLangOpts().OpenMP &&
+      Context.getLangOpts().OpenMPIsTargetDevice && isa<VarDecl>(D) &&
+      D->hasAttr<OMPDeclareTargetDeclAttr>() &&
+      D->getAttr<OMPDeclareTargetDeclAttr>()->getDevType() !=
+          OMPDeclareTargetDeclAttr::DT_NoHost) {
+    GV->setVisibility(llvm::GlobalValue::ProtectedVisibility);
+    return;
+  }
+
   // Set visibility for definitions, and for declarations if requested globally
   // or set explicitly.
   LinkageInfo LV = D->getLinkageAndVisibility();

clang/lib/CodeGen/Targets/AMDGPU.cpp

@@ -308,12 +308,13 @@ static bool requiresAMDGPUProtectedVisibility(const Decl *D,
   if (GV->getVisibility() != llvm::GlobalValue::HiddenVisibility)
     return false;
 
-  return D->hasAttr<OpenCLKernelAttr>() ||
-         (isa<FunctionDecl>(D) && D->hasAttr<CUDAGlobalAttr>()) ||
-         (isa<VarDecl>(D) &&
-          (D->hasAttr<CUDADeviceAttr>() || D->hasAttr<CUDAConstantAttr>() ||
-           cast<VarDecl>(D)->getType()->isCUDADeviceBuiltinSurfaceType() ||
-           cast<VarDecl>(D)->getType()->isCUDADeviceBuiltinTextureType()));
+  return !D->hasAttr<OMPDeclareTargetDeclAttr>() &&
+         (D->hasAttr<OpenCLKernelAttr>() ||
+          (isa<FunctionDecl>(D) && D->hasAttr<CUDAGlobalAttr>()) ||
+          (isa<VarDecl>(D) &&
+           (D->hasAttr<CUDADeviceAttr>() || D->hasAttr<CUDAConstantAttr>() ||
+            cast<VarDecl>(D)->getType()->isCUDADeviceBuiltinSurfaceType() ||
+            cast<VarDecl>(D)->getType()->isCUDADeviceBuiltinTextureType())));
 }
 
 void AMDGPUTargetCodeGenInfo::setFunctionDeclAttributes(

clang/test/OpenMP/declare_target_codegen.cpp

@@ -31,7 +31,7 @@
 // CHECK-DAG: @dy = {{protected | }}global i32 0,
 // CHECK-DAG: @bbb = {{protected | }}global i32 0,
 // CHECK-DAG: weak constant %struct.__tgt_offload_entry { ptr @bbb,
-// CHECK-DAG: @ccc = external global i32,
+// CHECK-DAG: @ccc = external {{protected | }}global i32,
 // CHECK-DAG: @ddd = {{protected | }}global i32 0,
 // CHECK-DAG: @hhh_decl_tgt_ref_ptr = weak global ptr null
 // CHECK-DAG: @ggg_decl_tgt_ref_ptr = weak global ptr null

clang/test/OpenMP/declare_target_constexpr_codegen.cpp

@@ -16,7 +16,7 @@ class A {
 public:
   static constexpr double pi = 3.141592653589793116;
 //.
-// CHECK: @_ZN1A2piE = linkonce_odr constant double 0x400921FB54442D18, comdat, align 8
+// CHECK: @_ZN1A2piE = linkonce_odr protected constant double 0x400921FB54442D18, comdat, align 8
 // CHECK: @_ZL9anotherPi = internal constant double 3.140000e+00, align 8
 // CHECK: @llvm.compiler.used = appending global [2 x ptr] [ptr @"__ZN1A2piE$ref", ptr @"__ZL9anotherPi$ref"], section "llvm.metadata"
 //.

clang/test/OpenMP/target_visibility.cpp

@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -debug-info-kind=limited -verify -fopenmp -x c++ -triple nvptx64-unknown-unknown -fopenmp-targets=nvptx64-nvidia-cuda -emit-llvm %s -fopenmp-is-target-device -o - | FileCheck %s
-// RUN: %clang_cc1 -debug-info-kind=limited -verify -fopenmp -x c++ -triple nvptx-unknown-unknown -fopenmp-targets=nvptx-nvidia-cuda -emit-llvm %s -fopenmp-is-target-device -o - | FileCheck %s
+// RUN: %clang_cc1 -debug-info-kind=limited -verify -fopenmp -x c++ -triple amdgcn-amd-amdhsa -fopenmp-targets=amdgcn-amd-amdhsa -emit-llvm %s -fopenmp-is-target-device -o - | FileCheck %s
 // expected-no-diagnostics
 
 
@@ -21,6 +21,14 @@ void B::bar() { A a; a.foo(); }
 void B::sbar() { A::sfoo(); }
 #pragma omp declare target to(B::bar, B::sbar)
 
+[[gnu::visibility("hidden")]] extern const int x = 0;
+#pragma omp declare target to(x) device_type(nohost)
+
+[[gnu::visibility("hidden")]] int y = 0;
+#pragma omp declare target to(y)
+
+// CHECK-DAG: @x = hidden{{.*}} constant i32 0
+// CHECK-DAG: @y = protected{{.*}} i32 0
 // CHECK-DAG: define hidden void @_ZN1B4sbarEv()
 // CHECK-DAG: define linkonce_odr hidden void @_ZN1A4sfooEv()
 // CHECK-DAG: define hidden void @_ZN1B3barEv(