[MLton] SSA vs SSA2
Sun, 20 Nov 2005 19:28:59 -0500 (EST)
[Moving from MLton-user to MLton]
>> I'd vote for SSA, since it is a slightly simpler intermediate language,
>> though there has been some argument for migrating all the optimizations
>> from SSA to SSA2 and then eliminating SSA.
> I don't think there is a significant difference in complexity between
> SSA and SSA2.
I agree that the difference isn't significant, but the advantage of SSA
over SSA2 is that the default is immutability. And most optimizations,
like loop-invariant code motion, are only sound for immutable
types/values. It's relatively easy to check for Ref/Array prims and
ref/array types in SSA, while in SSA2, any possible component could be
mutable. (Witness the recent shrinker bug.)