Issue 24118 - ICE / regression from 2.103.1 - segfault on CTFE only code in 2.104.2 and 2.105.0

[RazvanN7]

The problem here is that when a lambda is passed to a template instance, the lambda call is inlined in the template instance. The context of the lambda is __ctfe so the compiler decides to not create a lowering for it, however, the template instance is still generated (without the lowering) thus causing the current regression.

A general solution would be to mark template instances as not needing code generation when instantiated from a speculative context, however, this is not easy to implement given the current caching strategy of template instances.

Until we fix that, we need to bail out of not generating the compiler hook call to avoid ices in e2ir.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	24118	regression	ICE / regression from 2.103.1 - segfault on CTFE only code in 2.104.2 and 2.105.0

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + dmd#15578"

[RazvanN7]

cc @WalterBright

[maxhaton]

Is this issue not that we are generating code at all in __ctfe if statements?

[maxhaton]

Also commit message looks wrong

[RazvanN7]

Is this issue not that we are generating code at all in __ctfe if statements?

Nope, ctfe block is not generated, but template instances from it are.

[maxhaton]

Is this issue not that we are generating code at all in __ctfe if statements?

Nope, ctfe block is not generated, but template instances from it are.

I thought we fixed that oof

[maxhaton]

(This is another thing that a dependency graph would help with, more on that shortly)

[RazvanN7]

@maxhaton I tried to fix it in the past : #13359 but bumped into some issue in phobos that I did not know how to reduce. Will give it another shot these days.

[RazvanN7]

@maxhaton ok with this fix?

[maxhaton]

It looks ok although if possible having the tracegc && needsCodegen pattern as a variable would be good, if you can think of a clean way of doing it.

[RazvanN7]

@maxhaton Done.