Fix PR4975. Avoid referencing empty vector.

llvm-svn: 99840

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -6051,8 +6051,10 @@ void SelectionDAGISel::LowerArguments(BasicBlock *LLVMBB) {
     }
 
     if (!I->use_empty()) {
-      SDValue Res = DAG.getMergeValues(&ArgValues[0], NumValues,
+      SDValue Res;
-                                       SDB->getCurDebugLoc());
+      if (!ArgValues.empty())
+        Res = DAG.getMergeValues(&ArgValues[0], NumValues,
+                                 SDB->getCurDebugLoc());
       SDB->setValue(I, Res);
 
       // If this argument is live outside of the entry block, insert a copy from

llvm/test/CodeGen/Generic/2010-ZeroSizedArg.ll

@@ -0,0 +1,17 @@
+; RUN: llc < %s
+; PR4975
+
+%0 = type <{ [0 x i32] }>
+%union.T0 = type { }
+
+@.str = private constant [1 x i8] c" "
+
+define arm_apcscc void @t(%0) nounwind {
+entry:
+  %arg0 = alloca %union.T0
+  %1 = bitcast %union.T0* %arg0 to %0*
+  store %0 %0, %0* %1, align 1
+  ret void
+}
+
+declare arm_apcscc i32 @printf(i8*, ...)