[mlir] Fix remove-dead-values pass throws error when module has a name (#109990)

Fixes #107870.

We can allow the enclosing Module operation to have a symbol.
The check was likely originally not considering this case and intended
to catch symbols inside the region, not accounting that the walk would
visit the enclosing operation.

Author: Wheest

mlir/lib/Transforms/RemoveDeadValues.cpp

@@ -576,6 +576,8 @@ void RemoveDeadValues::runOnOperation() {
   // all symbol ops present in the IR are function-like, and all symbol user ops
   // present in the IR are call-like.
   WalkResult acceptableIR = module->walk([&](Operation *op) {
+    if (op == module)
+      return WalkResult::advance();
     if (isa<BranchOpInterface>(op) ||
         (isa<SymbolOpInterface>(op) && !isa<FunctionOpInterface>(op)) ||
         (isa<SymbolUserOpInterface>(op) && !isa<CallOpInterface>(op))) {

mlir/test/Transforms/remove-dead-values.mlir

@@ -1,13 +1,25 @@
 // RUN: mlir-opt %s -remove-dead-values -split-input-file -verify-diagnostics | FileCheck %s
 
 // The IR remains untouched because of the presence of a non-function-like
-// symbol op (module @dont_touch_unacceptable_ir).
+// symbol op inside the module (const @__dont_touch_unacceptable_ir).
 //
+module {
 // expected-error @+1 {{cannot optimize an IR with non-function symbol ops, non-call symbol user ops or branch ops}}
-module @dont_touch_unacceptable_ir {
-  func.func @has_cleanable_simple_op(%arg0 : i32) {
-    %non_live = arith.addi %arg0, %arg0 : i32
-    return
+  memref.global "private" constant @__dont_touch_unacceptable_ir : memref<i32> = dense<0>
+  func.func @main(%arg0: i32) -> i32 {
+    return %arg0 : i32
+  }
+}
+
+// -----
+
+// Dead values are removed from the IR even if the module has a name
+//
+module @named_module_acceptable {
+  func.func @main(%arg0: tensor<10xf32>) -> tensor<10xf32> {
+    %0 = tensor.empty() : tensor<10xbf16>
+    // CHECK-NOT: tensor.empty
+    return %arg0 : tensor<10xf32>
   }
 }