More graceful handling AbslHashValue when hlo module doesn't have ent…

…ry computation layout. Without the fix hash breaks on empty module such as absl:Hash(HloTestBase::CreateNewVerifiedModule()).

PiperOrigin-RevId: 685822286

xla/hlo/ir/BUILD

@@ -114,6 +114,21 @@ cc_library(
     ],
 )
 
+xla_cc_test(
+    name = "hlo_module_test",
+    srcs = ["hlo_module_test.cc"],
+    deps = [
+        ":hlo",
+        "//xla/tests:hlo_test_base",
+        "//xla/tests:verified_hlo_module",
+        "@com_google_absl//absl/hash",
+        "@com_google_googletest//:gtest_main",
+        "@tsl//tsl/platform:statusor",
+        "@tsl//tsl/platform:test",
+        "@tsl//tsl/platform:test_main",
+    ],
+)
+
 cc_library(
     name = "backend_config",
     srcs = ["backend_config.cc"],

xla/hlo/ir/hlo_module.h

@@ -287,7 +287,8 @@ class HloModule {
   // with respect to HloInstruction::Identical() method.
   template <typename H>
   friend H AbslHashValue(H h, const HloModule& module) {
-    h = H::combine(std::move(h), module.entry_computation_layout());
+    if (module.config().has_entry_computation_layout())
+      h = H::combine(std::move(h), module.entry_computation_layout());
     // Use MakeComputationSorted() instead of MakeComputationPostOrder()
     // because naming may affect the order of MakeComputationPostOrder() but not
     // MakeComputationSorted().

xla/hlo/ir/hlo_module_test.cc

@@ -0,0 +1,54 @@
+/* Copyright 2024 The OpenXLA Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+
+#include "xla/hlo/ir/hlo_module.h"
+
+#include <memory>
+#include <string_view>
+
+#include <gtest/gtest.h>
+#include "absl/hash/hash.h"
+#include "xla/tests/hlo_test_base.h"
+#include "xla/tests/verified_hlo_module.h"
+#include "tsl/platform/statusor.h"
+#include "tsl/platform/test.h"
+
+namespace xla {
+namespace {
+
+using HloModuleTest = HloTestBase;
+
+TEST_F(HloModuleTest, AbslHashValue) {
+  std::unique_ptr<HloModule> module1 = CreateNewVerifiedModule();
+  std::unique_ptr<HloModule> module2 = CreateNewVerifiedModule();
+  EXPECT_EQ(absl::HashOf(*module1), absl::HashOf(*module2));
+
+  std::string_view hlo = R"(
+      HloModule m1
+        ENTRY main {
+          a = f32[] parameter(0)
+          b = f32[] parameter(1)
+        ROOT res = f32[] multiply(a, b)
+      })";
+  TF_ASSERT_OK_AND_ASSIGN(std::unique_ptr<VerifiedHloModule> module3,
+                          ParseAndReturnVerifiedModule(hlo));
+  TF_ASSERT_OK_AND_ASSIGN(std::unique_ptr<VerifiedHloModule> module4,
+                          ParseAndReturnVerifiedModule(hlo));
+  EXPECT_EQ(absl::HashOf(*module3), absl::HashOf(*module4));
+  EXPECT_NE(absl::HashOf(*module1), absl::HashOf(*module4));
+}
+
+}  // namespace
+}  // namespace xla