[flang][cuda] Only copy global that have effective use (llvm#137890)

Author: clementval

flang/lib/Optimizer/Transforms/CUFDeviceGlobal.cpp

@@ -32,6 +32,15 @@ static void processAddrOfOp(fir::AddrOfOp addrOfOp,
                             mlir::SymbolTable &symbolTable,
                             llvm::DenseSet<fir::GlobalOp> &candidates,
                             bool recurseInGlobal) {
+
+  // Check if there is a real use of the global.
+  if (addrOfOp.getOperation()->hasOneUse()) {
+    mlir::OpOperand &addrUse = *addrOfOp.getOperation()->getUses().begin();
+    if (mlir::isa<fir::DeclareOp>(addrUse.getOwner()) &&
+        addrUse.getOwner()->use_empty())
+      return;
+  }
+
   if (auto globalOp = symbolTable.lookup<fir::GlobalOp>(
           addrOfOp.getSymbol().getRootReference().getValue())) {
     // TO DO: limit candidates to non-scalars. Scalars appear to have been

flang/test/Fir/CUDA/cuda-implicit-device-global.f90

@@ -329,3 +329,16 @@ // attributes(global) subroutine kernel4()
 // CHECK-LABEL: fir.global internal @_QFkernel4Ea : i32
 // CHECK-LABEL: gpu.module @cuda_device_mod
 // CHECK: fir.global internal @_QFkernel4Ea : i32
+
+// -----
+
+fir.global @_QMiso_c_bindingECc_alert constant : !fir.char<1>
+func.func @_QMcudafor_lib_internalsPfoo() attributes {cuf.proc_attr = #cuf.cuda_proc<global>} {
+  %19 = fir.address_of(@_QMiso_c_bindingECc_alert) : !fir.ref<!fir.char<1>>
+  %c1 = arith.constant 1 : index
+  %20 = fir.declare %19 typeparams %c1 {fortran_attrs = #fir.var_attrs<parameter>, uniq_name = "_QMiso_c_bindingECc_alert"} : (!fir.ref<!fir.char<1>>, index) -> !fir.ref<!fir.char<1>>
+ return
+}
+
+// CHECK-LABEL: gpu.module @cuda_device_mod
+// CHECK-NOT: _QMiso_c_bindingECc_alert