[NVPTX] noop when kernel pointers are already global

[jingyue]

Summary

Some front ends make kernel pointers global already. In that case,
handlePointerParams does nothing.

lib/Target/NVPTX/NVPTXLowerKernelArgs.cpp

void NVPTXLowerKernelArgs::handleByValParam(Argument *Arg) {
   LoadInst *LI = new LoadInst(ArgInParam, Arg->getName(), FirstInst);
   new StoreInst(LI, AllocA, FirstInst);
 }
 
 void NVPTXLowerKernelArgs::handlePointerParam(Argument *Arg) {
   assert(!Arg->hasByValAttr() &&
          "byval params should be handled by handleByValParam");
 
+  // Do nothing if the argument already points to the global address space.
+  if (Arg->getType()->getPointerAddressSpace() == ADDRESS_SPACE_GLOBAL)
+    return;
+
   Instruction *FirstInst = Arg->getParent()->getEntryBlock().begin();
   Instruction *ArgInGlobal = new AddrSpaceCastInst(
       Arg, PointerType::get(Arg->getType()->getPointerElementType(),
                             ADDRESS_SPACE_GLOBAL),
       Arg->getName(), FirstInst);
   Value *ArgInGeneric = new AddrSpaceCastInst(ArgInGlobal, Arg->getType(),
                                               Arg->getName(), FirstInst);
   // Replace with ArgInGeneric all uses of Args except ArgInGlobal.

test/CodeGen/NVPTX/lower-kernel-ptr-arg.ll

 ; CHECK: cvta.to.global.u64
   %1 = load float, float* %input, align 4
 ; CHECK: ld.global.f32
   store float %1, float* %output, align 4
 ; CHECK: st.global.f32
   ret void
 }
 
-!nvvm.annotations = !{!0}
+define void @kernel2(float addrspace(1)* %input, float addrspace(1)* %output) {
+; CHECK-LABEL: .visible .entry kernel2(
+; CHECK-NOT: cvta.to.global.u64
+  %1 = load float, float addrspace(1)* %input, align 4
+; CHECK: ld.global.f32
+  store float %1, float addrspace(1)* %output, align 4
+; CHECK: st.global.f32
+  ret void
+}
+
+!nvvm.annotations = !{!0, !1}
 !0 = !{void (float*, float*)* @kernel, !"kernel", i32 1}
+!1 = !{void (float addrspace(1)*, float addrspace(1)*)* @kernel2, !"kernel", i32 1}