Replace `==` with `eq` when determining unique types

When hash-consing TypeBounds, RefinedTypes and NamedTypes, we
now check the argument types with `eq`, where before it was `==`.
This is necessary for TypeBounds, because it makes a difference
whether a TypeBound has `eq` parts (then it is a type alias) or not.
So we cannot merge type aliases with non-aliases.

The symptom of the problem was when compiling Patterns.scala twice with
the new SeqLiterals phase (next commit) enabled. On second run, we encountered
an ArrayType[>: String <: String], even if we only created an ArrayType[String].
This was a consequence of the two types being identified by uniques.

Todo: Change the system so that type aliases are recognized more robustly.
But the present change seems to be useful anyway because it speeds up
uniques hashing. I verified that the stricter condition on uniques creates less
than 1% more types than before. So the speedup of hashing looks worthwhile.

1 files changed, 5 insertions, 4 deletions

diff --git a/src/dotty/tools/dotc/core/Uniques.scala b/src/dotty/tools/dotc/core/Uniques.scala
index 5e5b3e225..0ade58193 100644
--- a/src/dotty/tools/dotc/core/Uniques.scala
+++ b/src/dotty/tools/dotc/core/Uniques.scala
@@ -45,7 +45,7 @@ object Uniques {
     private def findPrevious(h: Int, prefix: Type, name: Name): NamedType = {
       var e = findEntryByHash(h)
       while (e != null) {
-        if ((e.prefix == prefix) && (e.name eq name)) return e
+        if ((e.prefix eq prefix) && (e.name eq name)) return e
         e = nextEntryByHash(h)
       }
       e
@@ -71,7 +71,7 @@ object Uniques {
     private def findPrevious(h: Int, lo: Type, hi: Type, variance: Int): TypeBounds = {
       var e = findEntryByHash(h)
       while (e != null) {
-        if ((e.lo == lo) && (e.hi == hi) && (e.variance == variance)) return e
+        if ((e.lo eq lo) && (e.hi eq hi) && (e.variance == variance)) return e
         e = nextEntryByHash(h)
       }
       e
@@ -87,7 +87,8 @@ object Uniques {
       if (h == NotCached) newBounds
       else {
         val r = findPrevious(h, lo, hi, variance)
-        if (r ne null) r else addEntryAfterScan(newBounds)
+        if (r ne null) r
+        else addEntryAfterScan(newBounds)
       }
     }
   }
@@ -99,7 +100,7 @@ object Uniques {
     private def findPrevious(h: Int, parent: Type, refinedName: Name, refinedInfo: Type): RefinedType = {
       var e = findEntryByHash(h)
       while (e != null) {
-        if ((e.parent == parent) && (e.refinedName eq refinedName) && (e.refinedInfo == refinedInfo))
+        if ((e.parent eq parent) && (e.refinedName eq refinedName) && (e.refinedInfo eq refinedInfo))
           return e
         e = nextEntryByHash(h)
       }