refactor: prepare null check redundancy analysis

this commit doesn't change any behavior

src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala

@@ -409,14 +409,14 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
 
         // example check: List[Int] <:< ::[Int]
         // TODO: extractor.paramType may contain unbound type params (run/t2800, run/t3530)
-        val (typeTestTreeMaker, patBinderOrCasted) =
+        val (typeTestTreeMaker, patBinderOrCasted, binderKnownNonNull) =
           if (needsTypeTest(patBinder.info.widen, extractor.paramType)) {
             // chain a type-testing extractor before the actual extractor call
             // it tests the type, checks the outer pointer and casts to the expected type
             // TODO: the outer check is mandated by the spec for case classes, but we do it for user-defined unapplies as well [SPEC]
             // (the prefix of the argument passed to the unapply must equal the prefix of the type of the binder)
             val treeMaker = TypeTestTreeMaker(patBinder, patBinder, extractor.paramType, extractor.paramType)(pos, extractorArgTypeTest = true)
-            (List(treeMaker), treeMaker.nextBinder)
+            (List(treeMaker), treeMaker.nextBinder, false)
           } else {
             // no type test needed, but the tree maker relies on `patBinderOrCasted` having type `extractor.paramType` (and not just some type compatible with it)
             // SI-6624 shows this is necessary because apparently patBinder may have an unfortunate type (.decls don't have the case field accessors)
@@ -426,10 +426,10 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
               if (settings.developer.value && !(patBinder.info =:= extractor.paramType))
                 devWarning(s"resetting info of $patBinder: ${patBinder.info} to ${extractor.paramType}")
             */
-            (Nil, patBinder setInfo extractor.paramType)
+            (Nil, patBinder setInfo extractor.paramType, false)
           }
 
-        withSubPats(typeTestTreeMaker :+ extractor.treeMaker(patBinderOrCasted, pos), extractor.subBindersAndPatterns: _*)
+        withSubPats(typeTestTreeMaker :+ extractor.treeMaker(patBinderOrCasted, binderKnownNonNull, pos), extractor.subBindersAndPatterns: _*)
       }
 
 
@@ -622,8 +622,13 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
       // to which type should the previous binder be casted?
       def paramType  : Type
 
-      // binder has been casted to paramType if necessary
-      def treeMaker(binder: Symbol, pos: Position): TreeMaker
+      /** Create the TreeMaker that embodies this extractor call
+       *
+       * `binder` has been casted to `paramType` if necessary
+       * `binderKnownNonNull` indicates whether the cast implies `binder` cannot be null
+       * when `binderKnownNonNull` is `true`, `ProductExtractorTreeMaker` does not do a (redundant) null check on binder
+       */
+      def treeMaker(binder: Symbol, binderKnownNonNull: Boolean, pos: Position): TreeMaker
 
       // `subPatBinders` are the variables bound by this pattern in the following patterns
       // subPatBinders are replaced by references to the relevant part of the extractor's result (tuple component, seq element, the result as-is)
@@ -731,8 +736,13 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
       def isSeq: Boolean = rawSubPatTypes.nonEmpty && isRepeatedParamType(rawSubPatTypes.last)
       protected def rawSubPatTypes = constructorTp.paramTypes
 
-      // binder has type paramType
-      def treeMaker(binder: Symbol, pos: Position): TreeMaker = {
+      /** Create the TreeMaker that embodies this extractor call
+       *
+       * `binder` has been casted to `paramType` if necessary
+       * `binderKnownNonNull` indicates whether the cast implies `binder` cannot be null
+       * when `binderKnownNonNull` is `true`, `ProductExtractorTreeMaker` does not do a (redundant) null check on binder
+       */
+      def treeMaker(binder: Symbol, binderKnownNonNull: Boolean, pos: Position): TreeMaker = {
         val paramAccessors = binder.constrParamAccessors
         // binders corresponding to mutable fields should be stored (SI-5158, SI-6070)
         val mutableBinders =
@@ -741,7 +751,7 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
           else Nil
 
         // checks binder ne null before chaining to the next extractor
-        ProductExtractorTreeMaker(binder, lengthGuard(binder))(subPatBinders, subPatRefs(binder), mutableBinders)
+        ProductExtractorTreeMaker(binder, lengthGuard(binder))(subPatBinders, subPatRefs(binder), mutableBinders, binderKnownNonNull)
       }
 
       // reference the (i-1)th case accessor if it exists, otherwise the (i-1)th tuple component
@@ -763,7 +773,12 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
       def resultType = tpe.finalResultType
       def isSeq      = extractorCall.symbol.name == nme.unapplySeq
 
-      def treeMaker(patBinderOrCasted: Symbol, pos: Position): TreeMaker = {
+       /** Create the TreeMaker that embodies this extractor call
+        *
+        * `binder` has been casted to `paramType` if necessary
+        * `binderKnownNonNull` is not used in this subclass
+        */
+      def treeMaker(patBinderOrCasted: Symbol, binderKnownNonNull: Boolean, pos: Position): TreeMaker = {
         // the extractor call (applied to the binder bound by the flatMap corresponding to the previous (i.e., enclosing/outer) pattern)
         val extractorApply = atPos(pos)(spliceApply(patBinderOrCasted))
         val binder         = freshSym(pos, pureType(resultInMonad)) // can't simplify this when subPatBinders.isEmpty, since UnitClass.tpe is definitely wrong when isSeq, and resultInMonad should always be correct since it comes directly from the extractor's result type
@@ -1081,7 +1096,8 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
     case class ProductExtractorTreeMaker(prevBinder: Symbol, extraCond: Option[Tree])(
           val subPatBinders: List[Symbol],
           val subPatRefs: List[Tree],
-          val mutableBinders: List[Symbol]) extends FunTreeMaker with PreserveSubPatBinders {
+          val mutableBinders: List[Symbol],
+          binderKnownNonNull: Boolean) extends FunTreeMaker with PreserveSubPatBinders {
 
       import CODE._
       val nextBinder = prevBinder // just passing through
@@ -1092,8 +1108,17 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
 
       def chainBefore(next: Tree)(casegen: Casegen): Tree = {
         val nullCheck = REF(prevBinder) OBJ_NE NULL
-        val cond = extraCond map (nullCheck AND _) getOrElse nullCheck
-        casegen.ifThenElseZero(cond, bindSubPats(substitution(next)))
+        val cond =
+          if (binderKnownNonNull) extraCond
+          else (extraCond map (nullCheck AND _)
+          orElse Some(nullCheck))
+
+        cond match {
+          case Some(cond) =>
+            casegen.ifThenElseZero(cond, bindSubPats(substitution(next)))
+          case _ =>
+            bindSubPats(substitution(next))
+        }
       }
 
       override def toString = "P"+(prevBinder.name,  extraCond getOrElse "", localSubstitution)