[turbofan] Fix representation changing for bigints

RepresentationChanger::GetTaggedPointerRepresentation did not handle
kCompressed cases correctly for BigInts. This led to a crash of BigInt
benchmarks in js-perf-test.

Bug: v8:9407
Change-Id: Id1d60a81afc528c8d4180bd5de9d237f2f0abd0a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1701848Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62718}

src/compiler/representation-change.cc

@@ -473,7 +473,20 @@ Node* RepresentationChanger::GetTaggedPointerRepresentationFor(
     }
     op = simplified()->CheckBigInt(use_info.feedback());
   } else if (output_rep == MachineRepresentation::kCompressedPointer) {
+    if (use_info.type_check() == TypeCheckKind::kBigInt &&
+        !output_type.Is(Type::BigInt())) {
+      node = InsertChangeCompressedToTagged(node);
+      op = simplified()->CheckBigInt(use_info.feedback());
+    } else {
+      op = machine()->ChangeCompressedPointerToTaggedPointer();
+    }
+  } else if (output_rep == MachineRepresentation::kCompressed &&
+             output_type.Is(Type::BigInt())) {
     op = machine()->ChangeCompressedPointerToTaggedPointer();
+  } else if (output_rep == MachineRepresentation::kCompressed &&
+             use_info.type_check() == TypeCheckKind::kBigInt) {
+    node = InsertChangeCompressedToTagged(node);
+    op = simplified()->CheckBigInt(use_info.feedback());
   } else if (CanBeCompressedSigned(output_rep) &&
              use_info.type_check() == TypeCheckKind::kHeapObject) {
     if (!output_type.Maybe(Type::SignedSmall())) {

test/mjsunit/compiler/bigint-add.js

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax --opt
+{
+  let a = 0n;
+  a = 3n;
+
+  function TestAdd() {
+    let sum = 0n;
+
+    for (let i = 0; i < 3; ++i) {
+      sum = a + sum;
+    }
+
+    return sum;
+  }
+
+  %PrepareFunctionForOptimization(TestAdd);
+  TestAdd();
+  TestAdd();
+  %OptimizeFunctionOnNextCall(TestAdd);
+  TestAdd();
+  TestAdd();
+}