[Mlir-commits] [mlir] [mlir] Fix crash in diagnostic verifier for unmatched @unknown expectations (PR #186148)

[Mehdi Amini]

https://github.com/joker-eph created https://github.com/llvm/llvm-project/pull/186148

When an expected-* directive uses the @unknown location specifier, the associated ExpectedDiag record has an invalid (null) SMLoc as its fileLoc. If the expected diagnostic is never produced, emitError() is called to report the unmatched expectation, but it unconditionally constructs an SMRange from fileLoc, triggering a null-pointer dereference (UBSan) and an assertion failure in SMRange's constructor which requires both endpoints to have equal validity.

Fix by guarding the SMRange construction with a fileLoc.isValid() check. When fileLoc is invalid, call PrintMessage without a source range.

Fixes #163343

Assisted-by: Claude Code

>From 899bd2c32a29acb6f6a3d476ef1a0991f77a7756 Mon Sep 17 00:00:00 2001
From: Mehdi Amini <joker.eph at gmail.com>
Date: Thu, 5 Mar 2026 03:24:09 -0800
Subject: [PATCH] [mlir] Fix crash in diagnostic verifier for unmatched
 @unknown expectations

When an expected-* directive uses the @unknown location specifier, the
associated ExpectedDiag record has an invalid (null) SMLoc as its fileLoc.
If the expected diagnostic is never produced, emitError() is called to
report the unmatched expectation, but it unconditionally constructs an
SMRange from fileLoc, triggering a null-pointer dereference (UBSan) and
an assertion failure in SMRange's constructor which requires both endpoints
to have equal validity.

Fix by guarding the SMRange construction with a fileLoc.isValid() check.
When fileLoc is invalid, call PrintMessage without a source range.

Fixes #163343
---
 mlir/lib/IR/Diagnostics.cpp                        | 14 +++++++++++---
 .../mlir-opt/expected-unknown-loc-unmatched.mlir   |  9 +++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 mlir/test/mlir-opt/expected-unknown-loc-unmatched.mlir

diff --git a/mlir/lib/IR/Diagnostics.cpp b/mlir/lib/IR/Diagnostics.cpp
index f4c9242ed3479..5caf826c84bdd 100644
--- a/mlir/lib/IR/Diagnostics.cpp
+++ b/mlir/lib/IR/Diagnostics.cpp
@@ -600,9 +600,17 @@ struct ExpectedDiag {
   /// Emit an error at the location referenced by this diagnostic.
   LogicalResult emitError(raw_ostream &os, llvm::SourceMgr &mgr,
                           const Twine &msg) {
-    SMRange range(fileLoc, SMLoc::getFromPointer(fileLoc.getPointer() +
-                                                 substring.size()));
-    mgr.PrintMessage(os, fileLoc, llvm::SourceMgr::DK_Error, msg, range);
+    // fileLoc may be invalid when the expected diagnostic used an unknown
+    // location specifier (e.g. `// expected-error @unknown {{...}}`). In that
+    // case, skip the source range to avoid a null-pointer dereference and an
+    // assertion in SMRange that both endpoints must have the same validity.
+    if (fileLoc.isValid()) {
+      SMRange range(fileLoc, SMLoc::getFromPointer(fileLoc.getPointer() +
+                                                   substring.size()));
+      mgr.PrintMessage(os, fileLoc, llvm::SourceMgr::DK_Error, msg, range);
+    } else {
+      mgr.PrintMessage(os, fileLoc, llvm::SourceMgr::DK_Error, msg);
+    }
     return failure();
   }
 
diff --git a/mlir/test/mlir-opt/expected-unknown-loc-unmatched.mlir b/mlir/test/mlir-opt/expected-unknown-loc-unmatched.mlir
new file mode 100644
index 0000000000000..5a06d386dabf8
--- /dev/null
+++ b/mlir/test/mlir-opt/expected-unknown-loc-unmatched.mlir
@@ -0,0 +1,9 @@
+// Test that an unmatched `expected-*` directive using the `@unknown` location
+// specifier emits a diagnostic instead of crashing.
+// See https://github.com/llvm/llvm-project/issues/163343
+
+// RUN: not mlir-opt --verify-diagnostics %s 2>&1 | FileCheck %s
+
+// CHECK: expected warning "some warning that is never produced" was not produced
+
+// expected-warning @unknown {{some warning that is never produced}}