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

[Perry Gibson]

https://github.com/Wheest created https://github.com/llvm/llvm-project/pull/109990

This fixes the error described in #107870, which I also independently experienced.

This implements the logic change suggested by @joker-eph.

This requires replacing one of the tests:

```mlir
// The IR remains untouched because of the presence of a non-function-like
// symbol op (module @dont_touch_unacceptable_ir).
//
// 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
  }
}
```

Since this asserts that named modules are not allowed, which is the behaviour we are trying to fix.  It is not clear to me why this assertion would be needed.

Anecdotally, I experienced the error going from StableHLO (which has named modules), and lowering.

>From bc80ab6746f5d1f220ff540f075704a5c0479f85 Mon Sep 17 00:00:00 2001
From: pez <perry at gibsonic.org>
Date: Wed, 25 Sep 2024 15:22:56 +0100
Subject: [PATCH] Fix remove-dead-values throws error w/module name

https://github.com/llvm/llvm-project/issues/107870
---
 mlir/lib/Transforms/RemoveDeadValues.cpp     |  1 +
 mlir/test/Transforms/remove-dead-values.mlir | 15 ++++++++-------
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/mlir/lib/Transforms/RemoveDeadValues.cpp b/mlir/lib/Transforms/RemoveDeadValues.cpp
index 055256903a1522..539797151dbbb7 100644
--- a/mlir/lib/Transforms/RemoveDeadValues.cpp
+++ b/mlir/lib/Transforms/RemoveDeadValues.cpp
@@ -576,6 +576,7 @@ 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))) {
diff --git a/mlir/test/Transforms/remove-dead-values.mlir b/mlir/test/Transforms/remove-dead-values.mlir
index 69426fdb620832..4622b6afa942de 100644
--- a/mlir/test/Transforms/remove-dead-values.mlir
+++ b/mlir/test/Transforms/remove-dead-values.mlir
@@ -1,13 +1,14 @@
 // 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).
+// -----
+
+// Dead values are removed from the IR even if the module has a name
 //
-// 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
+module @named_module_acceptable {
+  func.func @main(%arg0: tensor<10xf32>) -> tensor<10xf32> {
+    %0 = tensor.empty() : tensor<10xbf16>
+    // CHECK-NOT: %[[C:.*]] = tensor.empty[[C:.*]]
+    return %arg0 : tensor<10xf32>
   }
 }