From 8fcb94e134cae78fbc53be02e1d66948a3c28779 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Doeraene?= <sjrdoeraene@gmail.com>
Date: Tue, 7 Apr 2020 16:16:20 +0200
Subject: [PATCH] Use a fast path when looking up trait setter getters.

---
 .../src/dotty/tools/dotc/core/NameOps.scala    | 10 +++-------
 .../dotty/tools/dotc/transform/Memoize.scala   | 18 +++++++++++++-----
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/NameOps.scala b/compiler/src/dotty/tools/dotc/core/NameOps.scala
index 57e4be8cd4ce..550f3243df6e 100644
--- a/compiler/src/dotty/tools/dotc/core/NameOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/NameOps.scala
@@ -259,13 +259,9 @@ object NameOps {
     def setterName: TermName = name.exclude(FieldName) ++ str.SETTER_SUFFIX
 
     def getterName: TermName =
-      if name.is(TraitSetterName) then
-        val TraitSetterName(_, original) = name
-        original.getterName
-      else
-        name.exclude(FieldName).mapLast(n =>
-          if (n.endsWith(str.SETTER_SUFFIX)) n.take(n.length - str.SETTER_SUFFIX.length).asSimpleName
-          else n)
+      name.exclude(FieldName).mapLast(n =>
+        if (n.endsWith(str.SETTER_SUFFIX)) n.take(n.length - str.SETTER_SUFFIX.length).asSimpleName
+        else n)
 
     def fieldName: TermName =
       if (name.isSetterName)
diff --git a/compiler/src/dotty/tools/dotc/transform/Memoize.scala b/compiler/src/dotty/tools/dotc/transform/Memoize.scala
index bb23e6b5c7a9..4fb3d9876cfd 100644
--- a/compiler/src/dotty/tools/dotc/transform/Memoize.scala
+++ b/compiler/src/dotty/tools/dotc/transform/Memoize.scala
@@ -117,12 +117,20 @@ class Memoize extends MiniPhase with IdentityDenotTransformer { thisPhase =>
 
     def traitSetterGetter: Symbol =
       /* We have to compare SimpleNames here, because the setter name only
-       * embed the original getter's simple name, not its semantic name.
+       * embeds the original getter's simple name, not its semantic name.
+       * To mitigate the issue, we first try a fast path where we look up the
+       * simple name itself, which works for public fields.
        */
-      val getterSimpleName = sym.asTerm.name.getterName
-      sym.owner.info.decls.find { getter =>
-        getter.is(Accessor) && getter.asTerm.name.toSimpleName == getterSimpleName
-      }
+      val TraitSetterName(_, original) = sym.name
+      val getterSimpleName = original.getterName
+      val ownerInfo = sym.owner.info
+      val fastPath = ownerInfo.decl(getterSimpleName)
+      if fastPath.exists then
+        fastPath.symbol
+      else
+        ownerInfo.decls.find { getter =>
+          getter.is(Accessor) && getter.asTerm.name.toSimpleName == getterSimpleName
+        }
 
     if (sym.is(Accessor, butNot = NoFieldNeeded)
         && (!sym.name.is(TraitSetterName) || traitSetterGetter.is(Accessor, butNot = NoFieldNeeded))) {