Fix #9775: Fix primitive-in-condition handling in backend

isPrimitive/getPrimitive are overloaded: they both have a version which
takes a symbol as input and a version which takes a tree, the latter can
handle array get and set primitives which map to different JVM
instructions depending on their type, but we don't care about that when
emitting conditions in genCond: we only need to look for primitives
which correspond to boolean operations and those are already handled by
the symbol versions of isPrimitive/getPrimitive. By using these methods
in genCond we avoid running some unnecessary code and we fix #9775 which
was triggered because the `getPrimitive` overload we were using required
forcing `lhs`. This change also aligns us with what the scalac backend
does.

Author: smarter

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

@@ -1303,7 +1303,7 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
       lineNumber(tree)
       tree match {
 
-        case tree @ Apply(fun, args) if isPrimitive(fun) =>
+        case tree @ Apply(fun, args) if primitives.isPrimitive(fun.symbol) =>
           import ScalaPrimitivesOps.{ ZNOT, ZAND, ZOR, EQ }
 
           // lhs and rhs of test
@@ -1321,7 +1321,7 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
             genCond(rhs, success, failure, targetIfNoJump)
           }
 
-          primitives.getPrimitive(tree, lhs.tpe) match {
+          primitives.getPrimitive(fun.symbol) match {
             case ZNOT   => genCond(lhs, failure, success, targetIfNoJump)
             case ZAND   => genZandOrZor(and = true)
             case ZOR    => genZandOrZor(and = false)

tests/pos/i9775.scala

@@ -0,0 +1,13 @@
+trait ThreadedImpl {
+  private val threadSync = new AnyRef
+  @volatile private var wasClosed = false
+
+  private val thread: Thread = ???
+  val x: Array[Int] = ???
+
+  final protected def isThreadRunning: Boolean =
+    x(0)
+    // threadSync.synchronized(!wasClosed)
+    // true
+    thread.isAlive && threadSync.synchronized(!wasClosed)
+}