Merge pull request #4959 from sjrd/opt-char-tostring-in-fun-emitter

sjrd · web-flow · commit def28b514920 · 2024-03-16T14:09:58.000+01:00
Optimize `String_+` for `char` at the emitter level.
diff --git a/javalib/src/main/scala/java/lang/Character.scala b/javalib/src/main/scala/java/lang/Character.scala
@@ -118,7 +118,7 @@ object Character {
   @inline def hashCode(value: Char): Int = value.toInt
 
   @inline def toString(c: Char): String =
-    js.Dynamic.global.String.fromCharCode(c.toInt).asInstanceOf[String]
+    "" + c
 
   def toString(codePoint: Int): String = {
     if (isBmpCodePoint(codePoint)) {
diff --git a/linker/shared/src/main/scala/org/scalajs/linker/backend/emitter/CoreJSLib.scala b/linker/shared/src/main/scala/org/scalajs/linker/backend/emitter/CoreJSLib.scala
@@ -930,6 +930,9 @@ private[emitter] object CoreJSLib {
       defineFunction1(VarField.doubleToInt) { x =>
         Return(If(x > 2147483647, 2147483647, If(x < -2147483648, -2147483648, x | 0)))
       } :::
+      defineFunction1(VarField.charToString) { x =>
+        Return(Apply(genIdentBracketSelect(StringRef, "fromCharCode"), x :: Nil))
+      } :::
       condDefs(semantics.stringIndexOutOfBounds != CheckedBehavior.Unchecked)(
         defineFunction2(VarField.charAt) { (s, i) =>
           val r = varRef("r")
diff --git a/linker/shared/src/main/scala/org/scalajs/linker/backend/emitter/FunctionEmitter.scala b/linker/shared/src/main/scala/org/scalajs/linker/backend/emitter/FunctionEmitter.scala
@@ -2391,8 +2391,8 @@ private[emitter] class FunctionEmitter(sjsGen: SJSGen) {
 
         case BinaryOp(op, lhs, rhs) =>
           import BinaryOp._
-          val newLhs = transformExprNoChar(lhs)
-          val newRhs = transformExprNoChar(rhs)
+          val newLhs = transformExpr(lhs, preserveChar = (op == String_+))
+          val newRhs = transformExpr(rhs, preserveChar = (op == String_+))
 
           (op: @switch) match {
             case === | !== =>
@@ -2445,11 +2445,16 @@ private[emitter] class FunctionEmitter(sjsGen: SJSGen) {
               js.BinaryOp(JSBinaryOp.!==, newLhs, newRhs)
 
             case String_+ =>
-              if (lhs.tpe == StringType || rhs.tpe == StringType) {
-                js.BinaryOp(JSBinaryOp.+, newLhs, newRhs)
-              } else {
-                js.BinaryOp(JSBinaryOp.+, js.BinaryOp(JSBinaryOp.+,
-                    js.StringLiteral(""), newLhs), newRhs)
+              def charToString(t: js.Tree): js.Tree =
+                genCallHelper(VarField.charToString, t)
+
+              (lhs.tpe, rhs.tpe) match {
+                case (CharType, CharType) => charToString(newLhs) + charToString(newRhs)
+                case (CharType, _)        => charToString(newLhs) + newRhs
+                case (_, CharType)        => newLhs + charToString(newRhs)
+                case (StringType, _)      => newLhs + newRhs
+                case (_, StringType)      => newLhs + newRhs
+                case _                    => (js.StringLiteral("") + newLhs) + newRhs
               }
 
             case Int_+ => or0(js.BinaryOp(JSBinaryOp.+, newLhs, newRhs))
diff --git a/linker/shared/src/main/scala/org/scalajs/linker/backend/emitter/VarField.scala b/linker/shared/src/main/scala/org/scalajs/linker/backend/emitter/VarField.scala
@@ -157,6 +157,8 @@ private[emitter] object VarField {
   /** Box char. */
   final val bC = mk("$bC")
 
+  final val charToString = mk("$cToS")
+
   final val charAt = mk("$charAt")
 
   // Object helpers
