Cache signature in SingleDenotation for matchDegree; reduce denot calls in widens

[Cherry-picked 69c16f8]

Author: noti0na1

compiler/src/dotty/tools/dotc/core/Denotations.scala

@@ -621,6 +621,30 @@ object Denotations {
             throw ex
         case _ => Signature.NotAMethod
 
+    private var myCurrentJavaSig: Signature = uninitialized
+    private var myCurrentJavaSigRunId: RunId = NoRunId
+    private var myCurrentScala2Sig: Signature = uninitialized
+    private var myCurrentScala2SigRunId: RunId = NoRunId
+    private var myCurrentSig: Signature = uninitialized
+    private var myCurrentSigRunId: RunId = NoRunId
+
+    def currentSignature(sourceLanguage: SourceLanguage)(using Context): Signature = sourceLanguage match
+      case SourceLanguage.Java =>
+        if myCurrentJavaSigRunId != ctx.runId then
+          myCurrentJavaSig = signature(sourceLanguage)
+          myCurrentJavaSigRunId = ctx.runId
+        myCurrentJavaSig
+      case SourceLanguage.Scala2 =>
+        if myCurrentScala2SigRunId != ctx.runId then
+          myCurrentScala2Sig = signature(sourceLanguage)
+          myCurrentScala2SigRunId = ctx.runId
+        myCurrentScala2Sig
+      case SourceLanguage.Scala3 =>
+        if myCurrentSigRunId != ctx.runId then
+          myCurrentSig = signature(sourceLanguage)
+          myCurrentSigRunId = ctx.runId
+        myCurrentSig
+
     def derivedSingleDenotation(symbol: Symbol, info: Type, pre: Type = this.prefix, isRefinedMethod: Boolean = this.isRefinedMethod)(using Context): SingleDenotation =
       if ((symbol eq this.symbol) && (info eq this.info) && (pre eq this.prefix) && (isRefinedMethod == this.isRefinedMethod)) this
       else newLikeThis(symbol, info, pre, isRefinedMethod)
@@ -1023,8 +1047,8 @@ object Denotations {
         val thisLanguage = SourceLanguage(symbol)
         val otherLanguage = SourceLanguage(other.symbol)
         val commonLanguage = SourceLanguage.commonLanguage(thisLanguage, otherLanguage)
-        val sig = signature(commonLanguage)
-        val otherSig = other.signature(commonLanguage)
+        val sig = currentSignature(commonLanguage)
+        val otherSig = other.currentSignature(commonLanguage)
         sig.matchDegree(otherSig) match
           case FullMatch =>
             !alwaysCompareTypes || info.matches(other.info)

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1262,7 +1262,8 @@ object Types extends TypeUtils {
     final def widen(using Context): Type = this match
       case _: TypeRef | _: MethodOrPoly => this // fast path for most frequent cases
       case tp: TermRef => // fast path for next most frequent case
-        if tp.isOverloaded then tp else tp.underlying.widen
+        val denot = tp.denot
+        if denot.isOverloaded then tp else denot.info.widen
       case tp: SingletonType => tp.underlying.widen
       case tp: ExprType => tp.resultType.widen
       case tp =>
@@ -1276,15 +1277,20 @@ object Types extends TypeUtils {
      *  base type by applying one or more `underlying` dereferences.
      */
     final def widenSingleton(using Context): Type = stripped match {
-      case tp: SingletonType if !tp.isOverloaded => tp.underlying.widenSingleton
+      case tp: TermRef =>
+        val denot = tp.denot
+        if denot.isOverloaded then this else denot.info.widenSingleton
+      case tp: SingletonType => tp.underlying.widenSingleton
       case _ => this
     }
 
     /** Widen from TermRef to its underlying non-termref
      *  base type, while also skipping Expr types.
      */
     final def widenTermRefExpr(using Context): Type = stripTypeVar match {
-      case tp: TermRef if !tp.isOverloaded => tp.underlying.widenExpr.widenTermRefExpr
+      case tp: TermRef =>
+        val denot = tp.denot
+        if denot.isOverloaded then this else denot.info.widenExpr.widenTermRefExpr
       case _ => this
     }