Disallow lvalues as block arguments

Author: Simon Camphausen

mlir/lib/Target/Cpp/TranslateToCpp.cpp

@@ -987,9 +987,9 @@ static LogicalResult printFunctionBody(CppEmitter &emitter,
       if (emitter.hasValueInScope(arg))
         return functionOp->emitOpError(" block argument #")
                << arg.getArgNumber() << " is out of scope";
-      if (isa<ArrayType>(arg.getType()))
+      if (isa<ArrayType, LValueType>(arg.getType()))
         return functionOp->emitOpError("cannot emit block argument #")
-               << arg.getArgNumber() << " with array type";
+               << arg.getArgNumber() << " with type " << arg.getType();
       if (failed(
               emitter.emitType(block.getParentOp()->getLoc(), arg.getType()))) {
         return failure();

mlir/test/Target/Cpp/invalid_declare_variables_at_top.mlir

@@ -1,9 +1,20 @@
 // RUN: mlir-translate -split-input-file -declare-variables-at-top -mlir-to-cpp -verify-diagnostics %s
 
-// expected-error@+1 {{'func.func' op cannot emit block argument #0 with array type}}
+// expected-error@+1 {{'func.func' op cannot emit block argument #0 with type '!emitc.array<4xi8>'}}
 func.func @array_as_block_argument(!emitc.array<4xi8>) {
 ^bb0(%arg0 : !emitc.array<4xi8>):
   cf.br ^bb1(%arg0 : !emitc.array<4xi8>)
 ^bb1(%a : !emitc.array<4xi8>):
-   return
+  return
+}
+
+// -----
+
+// expected-error@+1 {{'emitc.func' op cannot emit block argument #0 with type '!emitc.lvalue<i32>'}}
+emitc.func @lvalue_as_block_argument() {
+^bb0:
+  %0 = "emitc.variable"() <{value = #emitc.opaque<"">}> : () -> !emitc.lvalue<i32>
+  cf.br ^bb1(%0 : !emitc.lvalue<i32>)
+^bb1(%a : !emitc.lvalue<i32>):
+  emitc.return
 }