[turbofan] Fix representation selection of CheckFloat64Hole.

Properly handle the case where the CheckFloat64Hole becomes a
no-op after RETYPE (because the feedback type is already Number).
We always need to pass the Number restriction type here.

Bug: chromium:895199
Change-Id: I96a949ba35db1e6d35abedddc4507c101d95b716
Reviewed-on: https://chromium-review.googlesource.com/c/1278804Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56622}

src/compiler/simplified-lowering.cc

@@ -3103,32 +3103,25 @@ class RepresentationSelector {
       }
       case IrOpcode::kCheckFloat64Hole: {
         Type const input_type = TypeOf(node->InputAt(0));
-        if (input_type.Is(Type::Number())) {
-          VisitNoop(node, truncation);
-        } else {
         CheckFloat64HoleMode mode =
             CheckFloat64HoleParametersOf(node->op()).mode();
-          switch (mode) {
-            case CheckFloat64HoleMode::kAllowReturnHole:
+        if (mode == CheckFloat64HoleMode::kAllowReturnHole) {
+          // If {mode} is allow-return-hole _and_ the {truncation}
+          // identifies NaN and undefined, we can just pass along
+          // the {truncation} and completely wipe the {node}.
           if (truncation.IsUnused()) return VisitUnused(node);
           if (truncation.IsUsedAsFloat64()) {
             VisitUnop(node, UseInfo::TruncatingFloat64(),
                       MachineRepresentation::kFloat64);
             if (lower()) DeferReplacement(node, node->InputAt(0));
-              } else {
-                VisitUnop(
-                    node,
-                    UseInfo(MachineRepresentation::kFloat64, Truncation::Any()),
-                    MachineRepresentation::kFloat64, Type::Number());
+            return;
           }
-              break;
-            case CheckFloat64HoleMode::kNeverReturnHole:
-              VisitUnop(
-                  node,
+        }
+        VisitUnop(node,
                   UseInfo(MachineRepresentation::kFloat64, Truncation::Any()),
                   MachineRepresentation::kFloat64, Type::Number());
-              break;
-          }
+        if (lower() && input_type.Is(Type::Number())) {
+          DeferReplacement(node, node->InputAt(0));
         }
         return;
       }

test/mjsunit/regress/regress-crbug-895199.js

+// Copyright 2018 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
+
+function foo() {
+  var a = new Array(2);
+  a[0] = 23.1234;
+  a[1] = 25.1234;
+  %DeoptimizeNow();
+  return a[2];
+}
+foo();
+foo();
+%OptimizeFunctionOnNextCall(foo);
+foo()