[mlir][emitc] Disallow !emitc.opaque pointers

Fordbids to express pointer via the `!emitc.opaque` type. Point the user
to use the `!emitc.ptr` type instead.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D124002

Author: marbre

mlir/lib/Dialect/EmitC/IR/EmitC.cpp

@@ -220,6 +220,11 @@ Type emitc::OpaqueType::parse(AsmParser &parser) {
     parser.emitError(loc) << "expected non empty string in !emitc.opaque type";
     return Type();
   }
+  if (value.back() == '*') {
+    parser.emitError(loc) << "pointer not allowed as outer type with "
+                             "!emitc.opaque, use !emitc.ptr instead";
+    return Type();
+  }
   if (parser.parseGreater())
     return Type();
   return get(parser.getContext(), value);

mlir/test/Dialect/EmitC/invalid_types.mlir

@@ -4,3 +4,10 @@ func.func @illegal_opaque_type_1() {
     // expected-error @+1 {{expected non empty string in !emitc.opaque type}}
     %1 = "emitc.variable"(){value = "42" : !emitc.opaque<"">} : () -> !emitc.opaque<"mytype">
 }
+
+// -----
+
+func.func @illegal_opaque_type_2() {
+    // expected-error @+1 {{pointer not allowed as outer type with !emitc.opaque, use !emitc.ptr instead}}
+    %1 = "emitc.variable"(){value = "nullptr" : !emitc.opaque<"int32_t*">} : () -> !emitc.opaque<"int32_t*">
+}

mlir/test/Dialect/EmitC/types.mlir

@@ -14,6 +14,8 @@ func.func @opaque_types() {
   emitc.call "f"() {template_args = [!emitc<"opaque<\"status_t\">">]} : () -> ()
   // CHECK-NEXT: !emitc.opaque<"std::vector<std::string>">
   emitc.call "f"() {template_args = [!emitc.opaque<"std::vector<std::string>">]} : () -> ()
+  // CHECK-NEXT: !emitc.opaque<"SmallVector<int*, 4>">
+  emitc.call "f"() {template_args = [!emitc.opaque<"SmallVector<int*, 4>">]} : () -> ()
 
   return
 }