[compiler] Don't call Type::Min/Max on the empty type.

This is a cleanup.

R=jarin@chromium.org

Bug: 
Change-Id: I1621fde3f2a7da03ceca781b96d5ffec44eb8168
Reviewed-on: https://chromium-review.googlesource.com/758373Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49225}

src/compiler/operation-typer.cc

@@ -287,22 +287,24 @@ Type* OperationTyper::NumberAbs(Type* type) {
     return Type::None();
   }
 
-  bool const maybe_nan = type->Maybe(Type::NaN());
-  bool const maybe_minuszero = type->Maybe(Type::MinusZero());
   type = Type::Intersect(type, Type::PlainNumber(), zone());
+  if (type->IsInhabited()) {
     double const max = type->Max();
     double const min = type->Min();
     if (min < 0) {
       if (type->Is(cache_.kInteger)) {
-      type = Type::Range(0.0, std::max(std::fabs(min), std::fabs(max)), zone());
+        type =
+            Type::Range(0.0, std::max(std::fabs(min), std::fabs(max)), zone());
       } else {
         type = Type::PlainNumber();
       }
     }
-  if (maybe_minuszero) {
+  }
+
+  if (type->Maybe(Type::NaN())) {
     type = Type::Union(type, cache_.kSingletonZero, zone());
   }
-  if (maybe_nan) {
+  if (type->Maybe(Type::MinusZero())) {
     type = Type::Union(type, Type::NaN(), zone());
   }
   return type;
@@ -683,6 +685,8 @@ Type* OperationTyper::NumberModulus(Type* lhs, Type* rhs) {
   DCHECK(lhs->Is(Type::Number()));
   DCHECK(rhs->Is(Type::Number()));
 
+  if (!lhs->IsInhabited() || !rhs->IsInhabited()) return Type::None();
+
   // Modulus can yield NaN if either {lhs} or {rhs} are NaN, or
   // {lhs} is not finite, or the {rhs} is a zero value.
   bool maybe_nan = lhs->Maybe(Type::NaN()) || rhs->Maybe(cache_.kZeroish) ||

src/compiler/typer.cc

@@ -461,6 +461,7 @@ Type* Typer::Visitor::ToInteger(Type* type, Typer* t) {
 Type* Typer::Visitor::ToLength(Type* type, Typer* t) {
   // ES6 section 7.1.15 ToLength ( argument )
   type = ToInteger(type, t);
+  if (!type->IsInhabited()) return Type::None();
   double min = type->Min();
   double max = type->Max();
   if (max <= 0.0) {

src/compiler/types.cc

@@ -67,13 +67,16 @@ bool Type::Contains(RangeType* range, i::Object* val) {
 // Min and Max computation.
 
 double Type::Min() {
+  DCHECK(this->IsInhabited());
   DCHECK(this->Is(Number()));
   if (this->IsBitset()) return BitsetType::Min(this->AsBitset());
   if (this->IsUnion()) {
     double min = +V8_INFINITY;
-    for (int i = 0, n = this->AsUnion()->Length(); i < n; ++i) {
+    for (int i = 1, n = this->AsUnion()->Length(); i < n; ++i) {
       min = std::min(min, this->AsUnion()->Get(i)->Min());
     }
+    Type* bitset = this->AsUnion()->Get(0);
+    if (bitset->IsInhabited()) min = std::min(min, bitset->Min());
     return min;
   }
   if (this->IsRange()) return this->AsRange()->Min();
@@ -83,13 +86,16 @@ double Type::Min() {
 }
 
 double Type::Max() {
+  DCHECK(this->IsInhabited());
   DCHECK(this->Is(Number()));
   if (this->IsBitset()) return BitsetType::Max(this->AsBitset());
   if (this->IsUnion()) {
     double max = -V8_INFINITY;
-    for (int i = 0, n = this->AsUnion()->Length(); i < n; ++i) {
+    for (int i = 1, n = this->AsUnion()->Length(); i < n; ++i) {
       max = std::max(max, this->AsUnion()->Get(i)->Max());
     }
+    Type* bitset = this->AsUnion()->Get(0);
+    if (bitset->IsInhabited()) max = std::max(max, bitset->Max());
     return max;
   }
   if (this->IsRange()) return this->AsRange()->Max();