Fix #6710: reverse code for dcmpg/dcmpl and fcmpg/fcmpl

Note that the test may only run with the bootstrapped compiler,
because the ConstFold in non-bootstrapped compiler is using
the wrongly generated byte-code.

Author: liufengyun

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

@@ -1236,11 +1236,11 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
           (tk: @unchecked) match {
             case LONG   => emit(asm.Opcodes.LCMP)
             case FLOAT  =>
-              if (op == LT || op == LE) emit(asm.Opcodes.FCMPG)
-              else emit(asm.Opcodes.FCMPL)
+              if (op == LT || op == LE) emit(asm.Opcodes.FCMPL)
+              else emit(asm.Opcodes.FCMPG)
             case DOUBLE =>
-              if (op == LT || op == LE) emit(asm.Opcodes.DCMPG)
-              else emit(asm.Opcodes.DCMPL)
+              if (op == LT || op == LE) emit(asm.Opcodes.DCMPL)
+              else emit(asm.Opcodes.DCMPG)
           }
           bc.emitIF(op, success)
         }

compiler/test/dotty/tools/dotc/BootstrappedOnlyCompilationTests.scala

@@ -113,6 +113,13 @@ class BootstrappedOnlyCompilationTests extends ParallelTesting {
     ).checkRuns()
   }
 
+  @Test def runBootstrappedOnly: Unit = {
+    implicit val testGroup: TestGroup = TestGroup("runBootstrappedOnly")
+    aggregateTests(
+      compileFilesInDir("tests/run-bootstrapped", withCompilerOptions),
+    ).checkRuns()
+  }
+
   // Pickling Tests ------------------------------------------------------------
   //
   // Pickling tests are very memory intensive and as such need to be run with a

tests/run-bootstrapped/i6710.scala

@@ -0,0 +1,23 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    // constant fold will fail for non-bootstrapped Dotty
+    assert(!(Float.NaN > 0.0))
+    assert(!(Float.NaN < 0.0))
+    assert(!(Double.NaN > 0.0))
+    assert(!(Double.NaN < 0.0))
+
+    val f: Float = Float.NaN
+    val d: Double = Double.NaN
+    assert(!(f > 0.0f))
+    assert(!(f < 0.0f))
+    assert(!(d > 0.0))
+    assert(!(d < 0.0))
+
+    // loop forever before the fix
+    var x = Double.NaN
+    while(x < 10.0) { x = x + 1; println(x) }
+    while(x > 10.0) { x = x + 1; println(x) }
+    do { x = x + 1; println(x) } while(x < 10.0)
+    do { x = x + 1; println(x) } while(x > 10.0)
+  }
+}