[turbofan] Introduce NumberFloor simplified operator.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 5ea84bd90cdfb11c5dc0011898b26f350783dd71..e11e7c4be16b32617668fc3c09cea118a2efb610 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -240,6 +240,7 @@ class Typer::Visitor : public Reducer {
   static Type* ToNumber(Type*, Typer*);
   static Type* ToObject(Type*, Typer*);
   static Type* ToString(Type*, Typer*);
+  static Type* NumberFloor(Type*, Typer*);
   static Type* NumberToInt32(Type*, Typer*);
   static Type* NumberToUint32(Type*, Typer*);
 
@@ -487,6 +488,12 @@ Type* Typer::Visitor::ToString(Type* type, Typer* t) {
   return Type::String();
 }
 
+// static
+Type* Typer::Visitor::NumberFloor(Type* type, Typer* t) {
+  DCHECK(type->Is(Type::Number()));
+  if (type->Is(t->cache_.kIntegerOrMinusZeroOrNaN)) return type;
+  return t->cache_.kIntegerOrMinusZeroOrNaN;
+}
 
 Type* Typer::Visitor::NumberToInt32(Type* type, Typer* t) {
   // TODO(neis): DCHECK(type->Is(Type::Number()));
@@ -1715,6 +1722,9 @@ Type* Typer::Visitor::TypeNumberShiftRightLogical(Node* node) {
   return Type::Unsigned32();
 }
 
+Type* Typer::Visitor::TypeNumberFloor(Node* node) {
+  return TypeUnaryOp(node, NumberFloor);
+}
 
 Type* Typer::Visitor::TypeNumberToInt32(Node* node) {
   return TypeUnaryOp(node, NumberToInt32);