Fix #7677: Fix comparisons involving NaN

This reverts the fix in 10cc2f8 which
was apparently incomplete since it doesn't handle i7677.scala correctly
and replace it by the original fix done in scalac in
scala/scala#5207. (It might have been possible
to fix the dotty version instead, but I'd rather keep the dotty backend
as close as possible to the scalac backend).

Since this commit contains code from scalac it is:

Co-Authored-By: Lukas Rytz <lukas.rytz@gmail.com>

Author: smarter

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

@@ -1224,23 +1224,20 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
     }
 
     /* Emit code to compare the two top-most stack values using the 'op' operator. */
-    private def genCJUMP(success: asm.Label, failure: asm.Label, op: TestOp, tk: BType, targetIfNoJump: asm.Label): Unit = {
-      if (targetIfNoJump == success) genCJUMP(failure, success, op.negate(), tk, targetIfNoJump)
+    private def genCJUMP(success: asm.Label, failure: asm.Label, op: TestOp, tk: BType, targetIfNoJump: asm.Label, negated: Boolean = false): Unit = {
+      if (targetIfNoJump == success) genCJUMP(failure, success, op.negate(), tk, targetIfNoJump, negated = !negated)
       else {
         if (tk.isIntSizedType) { // BOOL, BYTE, CHAR, SHORT, or INT
           bc.emitIF_ICMP(op, success)
         } else if (tk.isRef) { // REFERENCE(_) | ARRAY(_)
           bc.emitIF_ACMP(op, success)
         } else {
           import Primitives._
+          def useCmpG = if (negated) op == GT || op == GE else op == LT || op == LE
           (tk: @unchecked) match {
             case LONG   => emit(asm.Opcodes.LCMP)
-            case FLOAT  =>
-              if (op == LT || op == LE) emit(asm.Opcodes.FCMPL)
-              else emit(asm.Opcodes.FCMPG)
-            case DOUBLE =>
-              if (op == LT || op == LE) emit(asm.Opcodes.DCMPL)
-              else emit(asm.Opcodes.DCMPG)
+            case FLOAT  => emit(if (useCmpG) asm.Opcodes.FCMPG else asm.Opcodes.FCMPL)
+            case DOUBLE => emit(if (useCmpG) asm.Opcodes.DCMPG else asm.Opcodes.DCMPL)
           }
           bc.emitIF(op, success)
         }
@@ -1249,9 +1246,9 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
     }
 
     /* Emits code to compare (and consume) stack-top and zero using the 'op' operator */
-    private def genCZJUMP(success: asm.Label, failure: asm.Label, op: TestOp, tk: BType, targetIfNoJump: asm.Label): Unit = {
+    private def genCZJUMP(success: asm.Label, failure: asm.Label, op: TestOp, tk: BType, targetIfNoJump: asm.Label, negated: Boolean = false): Unit = {
       import Primitives._
-      if (targetIfNoJump == success) genCZJUMP(failure, success, op.negate(), tk, targetIfNoJump)
+      if (targetIfNoJump == success) genCZJUMP(failure, success, op.negate(), tk, targetIfNoJump, negated = !negated)
       else {
         if (tk.isIntSizedType) { // BOOL, BYTE, CHAR, SHORT, or INT
           bc.emitIF(op, success)
@@ -1261,18 +1258,17 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
             case NE => bc emitIFNONNULL success
           }
         } else {
+          def useCmpG = if (negated) op == GT || op == GE else op == LT || op == LE
           (tk: @unchecked) match {
             case LONG   =>
               emit(asm.Opcodes.LCONST_0)
               emit(asm.Opcodes.LCMP)
             case FLOAT  =>
               emit(asm.Opcodes.FCONST_0)
-              if (op == LT || op == LE) emit(asm.Opcodes.FCMPL)
-              else emit(asm.Opcodes.FCMPG)
+              emit(if (useCmpG) asm.Opcodes.FCMPG else asm.Opcodes.FCMPL)
             case DOUBLE =>
               emit(asm.Opcodes.DCONST_0)
-              if (op == LT || op == LE) emit(asm.Opcodes.DCMPL)
-              else emit(asm.Opcodes.DCMPG)
+              emit(if (useCmpG) asm.Opcodes.DCMPG else asm.Opcodes.DCMPL)
           }
           bc.emitIF(op, success)
         }
@@ -1287,8 +1283,8 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
        case ScalaPrimitivesOps.NE => Primitives.NE
        case ScalaPrimitivesOps.LT => Primitives.LT
        case ScalaPrimitivesOps.LE => Primitives.LE
-       case ScalaPrimitivesOps.GE => Primitives.GE
        case ScalaPrimitivesOps.GT => Primitives.GT
+       case ScalaPrimitivesOps.GE => Primitives.GE
      }
 
     /*

tests/run-bootstrapped/i6710.scala renamed to tests/run/i6710.scala

@@ -0,0 +1,15 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    val a: Double = Double.NaN
+    val eval = (a <= 0) || (10L <= 0)
+    assert(!eval)
+    val eval2 = (Double.NaN <= 0) || (10L <= 0)
+    assert(!eval2)
+
+    val b: Float = Float.NaN
+    val eval3 = (b <= 0) || (10L <= 0)
+    assert(!eval3)
+    val eval4 = (Float.NaN <= 0) || (10L <= 0)
+    assert(!eval4)
+  }
+}