When typing phi nodes, weaken union of integer constants to a range.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 594e4bd61369e5b0caa6830127ab211a698722ed..cbf23f7ff98d85acb227613826c12f7726488351 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -197,6 +197,7 @@ class Typer::Visitor : public Reducer {
 
   Bounds WrapContextBoundsForInput(Node* node);
   Type* Weaken(Node* node, Type* current_type, Type* previous_type);
+  Type* WeakenConstants(Type* type);
 
   Zone* zone() { return typer_->zone(); }
   Isolate* isolate() { return typer_->isolate(); }
@@ -555,11 +556,26 @@ Bounds Typer::Visitor::TypeSelect(Node* node) {
 }
 
 
+Type* Typer::Visitor::WeakenConstants(Type* type) {
+  Type* const integer = typer_->cache_.kInteger;
+  if (!type->Maybe(integer)) return type;
+  Type* myinteger = Type::Intersect(type, integer, zone());

[Jarin, 2015/09/14 08:06:29]

Could you come up with a better name than myinteger? (E.g.. integer_part or some
such.)

+  if (myinteger->NumConstants() <= 1) return type;
+  return Type::Union(
+      type, Type::Range(myinteger->Min(), myinteger->Max(), typer_->zone()),
+      typer_->zone());
+}
+
+
 Bounds Typer::Visitor::TypePhi(Node* node) {
   int arity = node->op()->ValueInputCount();
   Bounds bounds = Operand(node, 0);
   for (int i = 1; i < arity; ++i) {
     bounds = Bounds::Either(bounds, Operand(node, i), zone());
+    // In order to avoid huge unions, we weaken multiple integer constants
+    // to a single range.
+    bounds.upper = WeakenConstants(bounds.upper);
+    bounds.lower = WeakenConstants(bounds.lower);
   }
   return bounds;
 }