[turbofan][x64] Improve code generation for Float64LessThan with Float64Abs.

During instruction selection, match the pattern

  Float64LessThan(#0.0, Float64Abs(x))

which TurboFan generates for NumberToBoolean in the general case,
and which evaluates to false if x is 0, -0 or NaN, and compile this
to a simple (v)ucomisd using not_equal flags condition, which avoids
the costly Float64Abs.

Also consistently generate this pattern in TurboFan and the code
stubs/interpreter for ToBoolean.

R=mstarzinger@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2473923003
Cr-Commit-Position: refs/heads/master@{#40740}

src/code-stub-assembler.cc

@@ -879,9 +879,8 @@ void CodeStubAssembler::BranchIfToBooleanIsTrue(Node* value, Label* if_true,
                                           MachineType::Float64());
 
       // Check if the floating point {value} is neither 0.0, -0.0 nor NaN.
-      Node* zero = Float64Constant(0.0);
-      GotoIf(Float64LessThan(zero, value_value), if_true);
-      Branch(Float64LessThan(value_value, zero), if_true, if_false);
+      Branch(Float64LessThan(Float64Constant(0.0), Float64Abs(value_value)),
+             if_true, if_false);
     }
 
     Bind(&if_valueisother);

src/compiler/effect-control-linearizer.cc

@@ -913,15 +913,14 @@ EffectControlLinearizer::ValueEffectControl
 EffectControlLinearizer::LowerTruncateTaggedToBit(Node* node, Node* effect,
                                                   Node* control) {
   Node* value = node->InputAt(0);
-  Node* one = jsgraph()->Int32Constant(1);
   Node* zero = jsgraph()->Int32Constant(0);
   Node* fzero = jsgraph()->Float64Constant(0.0);
 
   // Collect effect/control/value triples.
   int count = 0;
-  Node* values[7];
-  Node* effects[7];
-  Node* controls[6];
+  Node* values[6];
+  Node* effects[6];
+  Node* controls[5];
 
   // Check if {value} is a Smi.
   Node* check_smi = ObjectIsSmi(value);
@@ -1012,20 +1011,12 @@ EffectControlLinearizer::LowerTruncateTaggedToBit(Node* node, Node* effect,
         simplified()->LoadField(AccessBuilder::ForHeapNumberValue()), value,
         eheapnumber, if_heapnumber);
 
-    // Check if {value} is either less than 0.0 or greater than 0.0.
-    Node* check =
-        graph()->NewNode(machine()->Float64LessThan(), fzero, value_value);
-    Node* branch = graph()->NewNode(common()->Branch(), check, if_heapnumber);
-
-    controls[count] = graph()->NewNode(common()->IfTrue(), branch);
+    // Check if {value} is not one of 0, -0, or NaN.
+    controls[count] = if_heapnumber;
     effects[count] = eheapnumber;
-    values[count] = one;
-    count++;
-
-    controls[count] = graph()->NewNode(common()->IfFalse(), branch);
-    effects[count] = eheapnumber;
-    values[count] =
-        graph()->NewNode(machine()->Float64LessThan(), value_value, fzero);
+    values[count] = graph()->NewNode(
+        machine()->Float64LessThan(), fzero,
+        graph()->NewNode(machine()->Float64Abs(), value_value));
     count++;
   }
   control = graph()->NewNode(common()->IfFalse(), branch_heapnumber);

src/compiler/x64/instruction-selector-x64.cc

@@ -1942,9 +1942,26 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
       case IrOpcode::kFloat64Equal:
         cont->OverwriteAndNegateIfEqual(kUnorderedEqual);
         return VisitFloat64Compare(selector, value, cont);
-      case IrOpcode::kFloat64LessThan:
+      case IrOpcode::kFloat64LessThan: {
+        Float64BinopMatcher m(value);
+        if (m.left().Is(0.0) && m.right().IsFloat64Abs()) {
+          // This matches the pattern
+          //
+          //   Float64LessThan(#0.0, Float64Abs(x))
+          //
+          // which TurboFan generates for NumberToBoolean in the general case,
+          // and which evaluates to false if x is 0, -0 or NaN. We can compile
+          // this to a simple (v)ucomisd using not_equal flags condition, which
+          // avoids the costly Float64Abs.
+          cont->OverwriteAndNegateIfEqual(kNotEqual);
+          InstructionCode const opcode =
+              selector->IsSupported(AVX) ? kAVXFloat64Cmp : kSSEFloat64Cmp;
+          return VisitCompare(selector, opcode, m.left().node(),
+                              m.right().InputAt(0), cont, false);
+        }
         cont->OverwriteAndNegateIfEqual(kUnsignedGreaterThan);
         return VisitFloat64Compare(selector, value, cont);
+      }
       case IrOpcode::kFloat64LessThanOrEqual:
         cont->OverwriteAndNegateIfEqual(kUnsignedGreaterThanOrEqual);
         return VisitFloat64Compare(selector, value, cont);
@@ -2205,14 +2222,28 @@ void InstructionSelector::VisitFloat64Equal(Node* node) {
   VisitFloat64Compare(this, node, &cont);
 }
 
-
 void InstructionSelector::VisitFloat64LessThan(Node* node) {
+  Float64BinopMatcher m(node);
+  if (m.left().Is(0.0) && m.right().IsFloat64Abs()) {
+    // This matches the pattern
+    //
+    //   Float64LessThan(#0.0, Float64Abs(x))
+    //
+    // which TurboFan generates for NumberToBoolean in the general case,
+    // and which evaluates to false if x is 0, -0 or NaN. We can compile
+    // this to a simple (v)ucomisd using not_equal flags condition, which
+    // avoids the costly Float64Abs.
+    FlagsContinuation cont = FlagsContinuation::ForSet(kNotEqual, node);
+    InstructionCode const opcode =
+        IsSupported(AVX) ? kAVXFloat64Cmp : kSSEFloat64Cmp;
+    return VisitCompare(this, opcode, m.left().node(), m.right().InputAt(0),
+                        &cont, false);
+  }
   FlagsContinuation cont =
       FlagsContinuation::ForSet(kUnsignedGreaterThan, node);
   VisitFloat64Compare(this, node, &cont);
 }
 
-
 void InstructionSelector::VisitFloat64LessThanOrEqual(Node* node) {
   FlagsContinuation cont =
       FlagsContinuation::ForSet(kUnsignedGreaterThanOrEqual, node);