[turbofan] Distinguish between change- and truncate-tagged-to-float64.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 7330e372b58b35a935224bfb43494655ad3cd8e2..afd09882830a479dcf69120cc3612fd19cc00893 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -1853,6 +1853,12 @@ Type* Typer::Visitor::TypeChangeTaggedToFloat64(Node* node) {
   return ChangeRepresentation(arg, Type::UntaggedFloat64(), zone());
 }
 
+Type* Typer::Visitor::TypeTruncateTaggedToFloat64(Node* node) {
+  Type* arg = Operand(node, 0);
+  // TODO(neis): DCHECK(arg->Is(Type::NumberOrUndefined()));
+  return ChangeRepresentation(arg, Type::UntaggedFloat64(), zone());
+}
+
 Type* Typer::Visitor::TypeChangeInt31ToTaggedSigned(Node* node) {
   Type* arg = Operand(node, 0);
   // TODO(neis): DCHECK(arg->Is(Type::Signed31()));