Fix issue with PredicateState hash implementation

Due to not initializing the template anywhere we incorrectly implemented the hash function leading to compile errors if anything attempts to use it. Fix this issue.

PiperOrigin-RevId: 553849088

xls/passes/BUILD

@@ -815,6 +815,20 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "predicate_state_test",
+    srcs = ["predicate_state_test.cc"],
+    deps = [
+        ":predicate_state",
+        "@com_google_absl//absl/hash",
+        "@com_google_absl//absl/strings:str_format",
+        "//xls/common:xls_gunit",
+        "//xls/common:xls_gunit_main",
+        "//xls/ir",
+        "//xls/ir:function_builder",
+    ],
+)
+
 cc_library(
     name = "narrowing_pass",
     srcs = ["narrowing_pass.cc"],

xls/passes/predicate_state.h

@@ -31,7 +31,7 @@ namespace xls {
 struct DefaultArm : public std::monostate {
   template <typename H>
   friend H AbslHashValue(H h, const DefaultArm& a) {
-    return H::Combine(h, std::monostate{});
+    return H::combine(std::move(h), std::monostate{});
   }
 
   template <typename Sink>

xls/passes/predicate_state_test.cc

@@ -0,0 +1,50 @@
+// Copyright 2023 The XLS 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 "xls/passes/predicate_state.h"
+
+#include "gtest/gtest.h"
+#include "absl/hash/hash.h"
+#include "absl/strings/str_format.h"
+#include "xls/ir/function_builder.h"
+#include "xls/ir/nodes.h"
+#include "xls/ir/package.h"
+
+namespace xls {
+
+namespace {
+
+TEST(PredicateState, Hash) {
+  EXPECT_NE(absl::Hash<PredicateState>()(PredicateState()),
+            absl::Hash<PredicateState>()(PredicateState(nullptr, 33)));
+}
+
+TEST(PredicateState, Stringify) {
+  Package p("test");
+  FunctionBuilder fb("test", &p);
+  BValue sel = fb.Select(
+      fb.Param("w", p.GetBitsType(2)),
+      {fb.Param("x", p.GetBitsType(12)), fb.Param("y", p.GetBitsType(12))},
+      fb.Param("z", p.GetBitsType(12)));
+  EXPECT_EQ(
+      absl::StrFormat("%v", PredicateState(sel.node()->As<Select>(), 0)),
+      absl::StrFormat("PredicateState[sel.%d: arm: 0]", sel.node()->id()));
+  EXPECT_EQ(absl::StrFormat("%v", PredicateState(sel.node()->As<Select>(),
+                                                 PredicateState::kDefaultArm)),
+            absl::StrFormat("PredicateState[sel.%d: arm: DEFAULT]",
+                            sel.node()->id()));
+}
+
+}  // namespace
+}  // namespace xls