[PATCH] D27028: Add intrinsics for constrained floating point operations

[Andy Kaylor via Phabricator via llvm-commits]

andrew.w.kaylor added a comment.

In https://reviews.llvm.org/D27028#613867, @mehdi_amini wrote:

> Having the llvm_unreachable right after the StringSwitch should achieve the same thing.


I'm not sure I understand what you're suggesting here.  If I do this:

  return StringSwitch<RoundingMode>(RoundingArg)
    .Case("round.dynamic",    rmDynamic)
    .Case("round.tonearest",  rmToNearest)
    .Case("round.downward",   rmDownward)
    .Case("round.upward",     rmUpward)
    .Case("round.towardzero", rmTowardZero);
  llvm_unreachable("Unexpected rounding mode argument in FP intrinsic!");

the llvm_unreachable statement is purely unreachable because the implicit default from StringSwitch will assert or dereference a null pointer.  The llvm_unreachable in this case effectively becomes a comment.  So what I'd like to do is this:

  return StringSwitch<RoundingMode>(RoundingArg)
    .Case("round.dynamic",    rmDynamic)
    .Case("round.tonearest",  rmToNearest)
    .Case("round.downward",   rmDownward)
    .Case("round.upward",     rmUpward)
    .Case("round.towardzero", rmTowardZero)
    .UnreachableDefault("Unexpected rounding mode argument in FP intrinsic!");

which at least in !NDEBUG builds will produce a useful message.  This would be fairly trivial to implement.


Repository:
  rL LLVM

https://reviews.llvm.org/D27028