Allow inline vals with alias to constant type

[nicolasstucki]

Allow inline vals with alias to constant type and make them constant fold

[plokhotnyuk]

@nicolasstucki Can constVal be used instead of c.eval from Scala 2 in compile-time?

I have a couple of use cases:

1. Expensive calculation of LUT tables that should happen in compile-time.
2. Passing of user defined configuration with "pure" functions that should be evaluated and used in compile-time during macro expansions.

[nicolasstucki]

@plokhotnyuk that kind of computation is out of the scope of inline val. Inline vals are basically an extension of the current final vals with constant RHS with the difference that the rhs must be a constant and hence is guaranteed to be inlined. What you describe seems to be still in the realm of macros.

[nicolasstucki]

@plokhotnyuk you could use the following macro (or something simillar)

  private final val f64Pow5InvSplit: Array[Long] = ${ evalF64Pow5InvSplit }
 
  // Put this in another file (not necessarily another project)
  // Contents of Expr evaluated at compiletime and result lifted into the code to create that array
  import scala.quoted._
  def evalF64Pow5InvSplit(using QuoteContext): Expr[Array[Long]] = Expr {
    val ss = new Array[Long](582)
    var pow5 = BigInt(1)
    var i = 0
    while (i < 582) {
      val inv = ((BigInt(1) << (pow5.bitLength + 121)) / pow5) + 1
      ss(i) = inv.longValue & 0x3FFFFFFFFFFFFFFFL
      ss(i + 1) = (inv >> 62).longValue & 0x3FFFFFFFFFFFFFFFL
      pow5 *= 5
      i += 2
    }
   ss
  }

[liufengyun]

LGTM

[liufengyun]

For later: maybe we should call .normalized, as dealias is just one of many possible normalization operations on types.

[nicolasstucki]

Yes, I have that in #8843. But when I tried to normalize it here it did not work. Maybe I need to deeply dealias and then normalize.