diff --git a/mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td b/mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td
--- a/mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td
+++ b/mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td
@@ -1337,8 +1337,9 @@
     /// Returns the result types of this function.
     ArrayRef<Type> getResultTypes() { return getFunctionType().getReturnTypes(); }
 
-    /// Returns the callable region, which is the function body.
-    Region *getCallableRegion() { return &getBody(); }
+    /// Returns the callable region, which is the function body. If the function
+    /// is external, returns null.
+    Region *getCallableRegion();
 
     /// Returns the callable result type, which is the function return type.
     ArrayRef<Type> getCallableResults() { return getFunctionType().getReturnTypes(); }
diff --git a/mlir/lib/Dialect/Arith/Transforms/UnsignedWhenEquivalent.cpp b/mlir/lib/Dialect/Arith/Transforms/UnsignedWhenEquivalent.cpp
--- a/mlir/lib/Dialect/Arith/Transforms/UnsignedWhenEquivalent.cpp
+++ b/mlir/lib/Dialect/Arith/Transforms/UnsignedWhenEquivalent.cpp
@@ -31,7 +31,7 @@
 /// non-negative.
 static LogicalResult staticallyNonNegative(DataFlowSolver &solver, Value v) {
   auto *result = solver.lookupState<IntegerValueRangeLattice>(v);
-  if (!result)
+  if (!result || result->getValue().isUninitialized())
     return failure();
   const ConstantIntRanges &range = result->getValue().getValue();
   return success(range.smin().isNonNegative());
diff --git a/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp b/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
--- a/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
+++ b/mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp
@@ -2184,6 +2184,12 @@
   return success();
 }
 
+Region *LLVMFuncOp::getCallableRegion() {
+  if (isExternal())
+    return nullptr;
+  return &getBody();
+}
+
 //===----------------------------------------------------------------------===//
 // Verification for LLVM::ConstantOp.
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/Arith/unsigned-when-equivalent.mlir b/mlir/test/Dialect/Arith/unsigned-when-equivalent.mlir
--- a/mlir/test/Dialect/Arith/unsigned-when-equivalent.mlir
+++ b/mlir/test/Dialect/Arith/unsigned-when-equivalent.mlir
@@ -86,3 +86,13 @@
     }
     func.return
 }
+
+func.func private @external() -> i8
+
+// CHECK-LABEL: @dead_code
+func.func @dead_code() {
+  %0 = call @external() : () -> i8
+  // CHECK: arith.floordivsi
+  %1 = arith.floordivsi %0, %0 : i8
+  return
+}
diff --git a/mlir/test/Dialect/LLVMIR/callgraph.mlir b/mlir/test/Dialect/LLVMIR/callgraph.mlir
--- a/mlir/test/Dialect/LLVMIR/callgraph.mlir
+++ b/mlir/test/Dialect/LLVMIR/callgraph.mlir
@@ -55,8 +55,7 @@
 module attributes {"test.name" = "Invoke call"} {
   // CHECK-LABEL: ---- CallGraph ----
   // CHECK: - Node : 'llvm.func' {{.*}} sym_name = "invokeLandingpad"
-  // CHECK-DAG: -- Call-Edge : 'llvm.func' {{.*}} sym_name = "foo"
-  // CHECK-DAG: -- Call-Edge : 'llvm.func' {{.*}} sym_name = "bar"
+  // CHECK-DAG: -- Call-Edge : <Unknown-Callee-Node>
 
   // CHECK: -- SCCs --
   llvm.mlir.global external constant @_ZTIi() : !llvm.ptr<i8>