Add mechanism to instruct VM's global analysis pass to try to const evaluate certain parts of a program before global analysis runs.

[mkustermann]

We can make our global analysis pass on the kernel recognize @pramga('vm:try-evaluate-as-constant') and try to constant evaluate it while a) supporting a subset of language b) recognizing the dart:io platform getters as constant.

[alexmarkov]

It would be nice to reuse/extend the existing constant evaluator which is used in the CFE, if that's possible. Note that there's also const-functions experimental flag (enabled with --enable-experiment=const-functions) which extends the constant evaluator abilities beyond current const expressions.

If we're doing this constant evaluation before TFA, then it would be useful to do that before or during unreachable code elimination pass which runs before TFA. That pass removes code guarded by constant conditions.

[a-siva]

Is P1 the right priority for this issue? According to our new issue triage policy we would need updates on a weekly basis on all P1 issues.

[mkustermann]

Is P1 the right priority for this issue? According to our new issue triage policy we would need updates on a weekly basis on all P1 issues.

@sstrickl is actively working on this and this is a high priority task. It may make sense to post regular updates (so interested stakeholders know how it's progressing)

[mkustermann]

To give some update here, @sstrickl landed 2c0484c as a first step, more to follow.

[a-siva]

After discussions with @mkustermann decided to lower prioirty of this issue.