Reduce SourcePosition allocations

Author: odersky

compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala

@@ -535,7 +535,7 @@ trait BCodeSkelBuilder extends BCodeHelpers {
     }
     def lineNumber(tree: Tree): Unit = {
       if (!emitLines || !tree.span.exists) return;
-      val nr = ctx.source.atSpan(tree.span).line + 1
+      val nr = ctx.source.offsetToLine(tree.span.point) + 1
       if (nr != lastEmittedLineNr) {
         lastEmittedLineNr = nr
         lastInsn match {

compiler/src/dotty/tools/dotc/util/SourcePosition.scala

@@ -25,7 +25,7 @@ extends SrcPos, interfaces.SourcePosition, Showable {
 
   def point: Int = span.point
 
-  def line: Int = if (source.content().length != 0) source.offsetToLine(point) else -1
+  def line: Int = if (source.length != 0) source.offsetToLine(point) else -1
 
   /** Extracts the lines from the underlying source file as `Array[Char]`*/
   def linesSlice: Array[Char] =