Issue 15450 - ICE during CTFE of legit function

[9rnsr]

ForeachStatement didn't set LabelStatement.gotoTarget correctly, so it had broke the jump behavior during CTFE.

Don't use sc2 for the checkLabeledLoop argument in ForeachStatement.semantic, because sc2.slabel is not same with sc.slabel. (it's reset to null in sc.push()).

[dlang-bot]

Fix	Bugzilla	Description
✓	15450	ICE during CTFE of legit function

[WalterBright]

Please put refactorings in separate PRs. The actual bug fix here is just a handful of lines, but it comes with 240 more lines of changes. Even b09f2d8 is mostly refactorings.

[9rnsr]

@WalterBright Refactoring PR is normally left, so subsequent bugfix would also be left. So in order to fix the bug quickly, I should combine the refactorings and bugfix in a PR.

In this case, I cannot understand why the refactoring part should go into other PR. It has no benefit.

[9il]

I am not a DMD contributor, but I'll try to be objective.

@9rnsr fixes a lot issues, and he is doing this quick.
I understand that existing DMD contributors already understand DMD front-end. However for a common Phobos contributor this code looks very inconvenient end this force him to do not make PRs and only reports bugs. So this work is important.

@WalterBright I understand that it tooks a lot of yours time to review refactoring and changes. But D/Phobos idiomatic style allows other D contributors to made PRs by they self, and probably some of them will be a part of DMD reviewers team in the future. So you will be able to spend more time for more important questions rather than review :-)

In addition, I am worrying about #5309

Thank you all for fastest compiler ever!

[WalterBright]

I have explained the benefit multiple times in these PRs.

[WalterBright]

The other issue I have with this is the use of scope(exit). The trouble is that it sets up an exception handler frame to do this, and that's slower, even though no exceptions are thrown (none of the functions in the body are marked 'nothrow'). I want to be very parsimonious in adding in things that may slow the compiler down.

We should also improve the compiler so using scope is less impactful, but we aren't there yet.

So, I'll pull this if b09f2d8 is the whole PR, and the scope(exit) refactoring is not part of it.

[WalterBright]

Rebased and rebooted as #5336 as Kenji's bug fix but without the refactoring and reformatting.