Merge pull request scala#4863 from retronym/topic/leaner-patmat-codegen

DRY-er trees in pattern matcher code gen.

Author: lrytz

src/compiler/scala/tools/nsc/transform/patmat/MatchCodeGen.scala

@@ -55,7 +55,15 @@ trait MatchCodeGen extends Interface {
       def flatMap(prev: Tree, b: Symbol, next: Tree): Tree
       def flatMapCond(cond: Tree, res: Tree, nextBinder: Symbol, next: Tree): Tree
       def flatMapGuard(cond: Tree, next: Tree): Tree
-      def ifThenElseZero(c: Tree, thenp: Tree): Tree = IF (c) THEN thenp ELSE zero
+      def ifThenElseZero(c: Tree, thenp: Tree): Tree = {
+        val z = zero
+        thenp match {
+          case If(c1, thenp1, elsep1) if z equalsStructure elsep1 =>
+            If(c AND c1, thenp1, elsep1) // cleaner, leaner trees
+          case _ =>
+            If(c, thenp, zero)
+        }
+      }
       protected def zero: Tree
     }
 

test/files/run/t6288.check

@@ -33,11 +33,8 @@
       [175]case <synthetic> val x1: [175]Any = [175]"";
       [175]case5()[195]{
         [195]<synthetic> val o7: [195]Option[List[Int]] = [195][195]Case4.unapplySeq([195]x1);
-        [195]if ([195]o7.isEmpty.unary_!)
-          [195]if ([195][195][195][195]o7.get.!=([195]null).&&([195][195][195][195]o7.get.lengthCompare([195]1).==([195]0)))
-            [208][208]matchEnd4([208]())
-          else
-            [195][195]case6()
+        [195]if ([195][195]o7.isEmpty.unary_!.&&([195][195][195][195]o7.get.!=([195]null).&&([195][195][195][195]o7.get.lengthCompare([195]1).==([195]0))))
+          [208][208]matchEnd4([208]())
         else
           [195][195]case6()
       };
@@ -59,11 +56,8 @@
       [273]case <synthetic> val x1: [273]Any = [273]"";
       [273]case5()[293]{
         [293]<synthetic> val o7: [293]Option[List[Int]] = [293][293]Case4.unapplySeq([293]x1);
-        [293]if ([293]o7.isEmpty.unary_!)
-          [293]if ([293][293][293][293]o7.get.!=([293]null).&&([293][293][293][293]o7.get.lengthCompare([293]0).==([293]0)))
-            [304][304]matchEnd4([304]())
-          else
-            [293][293]case6()
+        [293]if ([293][293]o7.isEmpty.unary_!.&&([293][293][293][293]o7.get.!=([293]null).&&([293][293][293][293]o7.get.lengthCompare([293]0).==([293]0))))
+          [304][304]matchEnd4([304]())
         else
           [293][293]case6()
       };