[MLIR] Add verification that symbol operations must not have results (#168390)

This patch adds verification to the `SymbolOpInterface` to enforce the
design constraint that symbol operations must not produce SSA results,
as documented in [Symbols and
SymbolTables](https://mlir.llvm.org/docs/SymbolsAndSymbolTables/#defining-or-declaring-a-symbol).

This is a follow-up of #168376

Author: timnoack

mlir/include/mlir/IR/SymbolInterfaces.td

@@ -171,6 +171,8 @@ def Symbol : OpInterface<"SymbolOpInterface"> {
     if (concreteOp.isDeclaration() && concreteOp.isPublic())
       return concreteOp.emitOpError("symbol declaration cannot have public "
              "visibility");
+    if ($_op->getNumResults() != 0)
+      return concreteOp.emitOpError("symbols must not have results");
     auto parent = $_op->getParentOp();
     if (parent && !parent->hasTrait<OpTrait::SymbolTable>() && parent->isRegistered()) {
       return concreteOp.emitOpError("symbol's parent must have the SymbolTable "

mlir/test/IR/invalid-ops.mlir

@@ -145,3 +145,11 @@ func.func @verify_fail_3() {
   %r = "arith.constant"() {value = -3 : si32} : () -> si32
   return
 }
+
+// -----
+
+// Verify that symbols with results are rejected
+module {
+  // expected-error@+1 {{'test.symbol_with_result' op symbols must not have results}}
+  %0 = "test.symbol_with_result"() <{sym_name = "test_symbol"}> : () -> i32
+}

mlir/test/lib/Dialect/Test/TestOps.td

@@ -120,6 +120,13 @@ def SymbolOp : TEST_Op<"symbol", [NoMemoryEffect, Symbol]> {
                        OptionalAttr<StrAttr>:$sym_visibility);
 }
 
+def SymbolWithResultOp : TEST_Op<"symbol_with_result", [Symbol]> {
+  let summary = "invalid symbol operation that produces an SSA result";
+  let arguments = (ins StrAttr:$sym_name,
+                       OptionalAttr<StrAttr>:$sym_visibility);
+  let results = (outs AnyType:$result);
+}
+
 def OverriddenSymbolVisibilityOp : TEST_Op<"overridden_symbol_visibility", [
   DeclareOpInterfaceMethods<Symbol, ["getVisibility", "setVisibility"]>,
 ]> {