6502: always fold constants

src/main/scala/millfork/compiler/mos/MosExpressionCompiler.scala

@@ -344,6 +344,14 @@ object MosExpressionCompiler extends AbstractExpressionCompiler[AssemblyLine] {
 
   def compile(ctx: CompilationContext, expr: Expression, exprTypeAndVariable: Option[(Type, Variable)], branches: BranchSpec): List[AssemblyLine] = {
     val env = ctx.env
+    env.eval(expr) match {
+      case Some(value) =>
+        return exprTypeAndVariable.fold(noop) { case (exprType, target) =>
+          assertCompatible(exprType, target.typ)
+          compileConstant(ctx, value, target)
+        }
+      case _ =>
+    }
     val b = env.get[Type]("byte")
     val w = env.get[Type]("word")
     expr match {

src/test/scala/millfork/test/ConstantSuite.scala

@@ -0,0 +1,23 @@
+package millfork.test
+
+import millfork.Cpu
+import millfork.test.emu.EmuUnoptimizedCrossPlatformRun
+import org.scalatest.{FunSuite, Matchers}
+
+/**
+  * @author Karol Stasiak
+  */
+class ConstantSuite extends FunSuite with Matchers {
+
+    test("Constants should fold") {
+      EmuUnoptimizedCrossPlatformRun(Cpu.Mos, Cpu.Z80)(
+        """
+          | array Sieve[4]
+          | array __screen[4]
+          | byte vic_mem
+          | void main() {
+          |   vic_mem = lo( ((Sieve.addr >> 10) & 8) | ((__screen.addr >> 6) & $f0) )
+          | }
+        """.stripMargin){m => }
+    }
+}