[arm64][turbofan] Fix implementation of Float64Min.

ARM64's `fmin` and `fmax` instructions don't have the same behaviour as
TurboFan's Float(32|64)(Min|Max) functions.

BUG=4206
LOG=N

Review URL: https://codereview.chromium.org/1200123004

Cr-Commit-Position: refs/heads/master@{#29229}

src/compiler/arm64/instruction-selector-arm64.cc

@@ -1282,24 +1282,16 @@ void InstructionSelector::VisitFloat64Mod(Node* node) {
 }
 
 
-void InstructionSelector::VisitFloat32Max(Node* node) {
-  VisitRRR(this, kArm64Float32Max, node);
-}
+void InstructionSelector::VisitFloat32Max(Node* node) { UNREACHABLE(); }
 
 
-void InstructionSelector::VisitFloat64Max(Node* node) {
-  VisitRRR(this, kArm64Float64Max, node);
-}
+void InstructionSelector::VisitFloat64Max(Node* node) { UNREACHABLE(); }
 
 
-void InstructionSelector::VisitFloat32Min(Node* node) {
-  VisitRRR(this, kArm64Float32Min, node);
-}
+void InstructionSelector::VisitFloat32Min(Node* node) { UNREACHABLE(); }
 
 
-void InstructionSelector::VisitFloat64Min(Node* node) {
-  VisitRRR(this, kArm64Float64Min, node);
-}
+void InstructionSelector::VisitFloat64Min(Node* node) { UNREACHABLE(); }
 
 
 void InstructionSelector::VisitFloat32Abs(Node* node) {
@@ -2009,11 +2001,7 @@ void InstructionSelector::VisitFloat64InsertHighWord32(Node* node) {
 // static
 MachineOperatorBuilder::Flags
 InstructionSelector::SupportedMachineOperatorFlags() {
-  return MachineOperatorBuilder::kFloat32Max |
-         MachineOperatorBuilder::kFloat32Min |
-         MachineOperatorBuilder::kFloat64Max |
-         MachineOperatorBuilder::kFloat64Min |
-         MachineOperatorBuilder::kFloat64RoundDown |
+  return MachineOperatorBuilder::kFloat64RoundDown |
          MachineOperatorBuilder::kFloat64RoundTruncate |
          MachineOperatorBuilder::kFloat64RoundTiesAway |
          MachineOperatorBuilder::kWord32ShiftIsSafe |

src/compiler/machine-operator.h

@@ -88,6 +88,8 @@ class MachineOperatorBuilder final : public ZoneObject {
   // for operations that are unsupported by some back-ends.
   enum Flag {
     kNoFlags = 0u,
+    // Note that Float*Max behaves like `(a < b) ? b : a`, not like Math.max().
+    // Note that Float*Min behaves like `(a < b) ? a : b`, not like Math.min().
     kFloat32Max = 1u << 0,
     kFloat32Min = 1u << 1,
     kFloat64Max = 1u << 2,

test/mjsunit/compiler/regress-4206.js

+// Copyright 2015 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.
+
+function Module(stdlib) {
+  "use asm";
+  function TernaryMin(a, b) {
+    a=+(a);
+    b=+(b);
+    return (+((a < b) ? a : b));
+  }
+  function TernaryMax(a, b) {
+    a=+(a);
+    b=+(b);
+    return (+((b < a) ? a : b));
+  }
+  return { TernaryMin: TernaryMin,
+           TernaryMax: TernaryMax };
+}
+var min = Module(this).TernaryMin;
+var max = Module(this).TernaryMax;
+
+assertEquals(0.0, min(-0.0, 0.0));
+assertEquals(0.0, min(NaN, 0.0));
+assertEquals(-0.0, min(NaN, -0.0));
+assertEquals(-0.0, max(0.0, -0.0));
+assertEquals(0.0, max(NaN, 0.0));
+assertEquals(-0.0, max(NaN, -0.0));