[AMDGPU] Re-enable closed-world assumption as an opt-out feature

Although the ABI (if any exists) doesn’t explicitly prohibit cross-device-image
function calls, especially since our loader can handle them, for all officially
supported programming models, this is not actually allowed. Given this, assuming
a closed-world model at link time is safe. However, there are certain cases,
such as the GPU libc project, that use non-standard approaches which could break
this assumption. This PR introduces an option to disable this assumption when
needed.

Author: shiltian

llvm/lib/Target/AMDGPU/AMDGPUAttributor.cpp

@@ -1286,6 +1286,10 @@ static bool runImpl(Module &M, AnalysisGetter &AG, TargetMachine &TM,
 
   Attributor A(Functions, InfoCache, AC);
 
+  LLVM_DEBUG(dbgs() << "[AMDGPUAttributor] Module " << M.getName() << " is "
+                    << (AC.IsClosedWorldModule ? "" : "not ")
+                    << "assumed to be a closed world.\n");
+
   for (auto *F : Functions) {
     A.getOrCreateAAFor<AAAMDAttributes>(IRPosition::function(*F));
     A.getOrCreateAAFor<AAUniformWorkGroupSize>(IRPosition::function(*F));

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -454,6 +454,11 @@ static cl::opt<bool> NewRegBankSelect(
              "regbankselect"),
     cl::init(false), cl::Hidden);
 
+static cl::opt<bool> HasClosedWorldAssumption(
+    "amdgpu-link-time-closed-world",
+    cl::desc("Whether has closed-world assumption at link time"),
+    cl::init(false), cl::Hidden);
+
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAMDGPUTarget() {
   // Register the target
   RegisterTargetMachine<R600TargetMachine> X(getTheR600Target());
@@ -859,8 +864,12 @@ void AMDGPUTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB) {
             PM.addPass(InternalizePass(mustPreserveGV));
             PM.addPass(GlobalDCEPass());
           }
-          if (EnableAMDGPUAttributor)
-            PM.addPass(AMDGPUAttributorPass(*this));
+          if (EnableAMDGPUAttributor) {
+            AMDGPUAttributorOptions Opt;
+            if (HasClosedWorldAssumption)
+              Opt.IsClosedWorld = true;
+            PM.addPass(AMDGPUAttributorPass(*this, Opt));
+          }
         }
       });
 

llvm/test/LTO/AMDGPU/closed-world-assumption.ll

@@ -0,0 +1,12 @@
+; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -O3 -debug-only=amdgpu-attributor -o - %s 2>&1 | FileCheck %s --check-prefix=NO-CW
+; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -passes="lto<O3>" -debug-only=amdgpu-attributor -o - %s 2>&1 | FileCheck %s --check-prefix=NO-CW
+; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -passes="lto<O3>" -debug-only=amdgpu-attributor -amdgpu-link-time-closed-world=1 -o - %s 2>&1 | FileCheck %s --check-prefix=CW
+
+; REQUIRES: amdgpu-registered-target
+; REQUIRES: asserts
+
+; NO-CW: Module {{.*}} is not assumed to be a closed world.
+; CW: Module {{.*}} is assumed to be a closed world.
+define hidden noundef i32 @_Z3foov() {
+  ret i32 1
+}