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[Miri] Use a session variable instead of checking for an env var always - #69888

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[Miri] Use a session variable instead of checking for an env var always#69888
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@wesleywiser

@wesleywiserwesleywiser commented Mar 10, 2020

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In CTFE heavy code, checking the env var everytime is inefficient. We
can do a lot better by using a Session variable instead.

r? @RalfJung

Part of #69297

@rust-highfiverust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 10, 2020
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Comment threadsrc/librustc_session/session.rs Outdated

@RalfJungRalfJungMar 10, 2020

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Suggested change
/// Capture a backtrace at the point the error is created and return it in the error.
/// Capture a backtrace at the point the error is created and return it in the error
/// (to be printed later if/when the error ever actually gets shown to the user).

@RalfJung

RalfJung commented Mar 10, 2020

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LGTM aside from the nit, but this is also touching global compiler infrastructure that I know little about... @oli-obk does this look reasonable?

@oli-obk

oli-obk commented Mar 10, 2020

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Yea this is OK, but at this point you could also just use a lazy static inside that function without affecting any code outside of it

@RalfJung

RalfJung commented Mar 10, 2020

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But then how is Miri going to change its value at run-time?

@oli-obk

oli-obk commented Mar 10, 2020

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You can lazily initialize from the env var. Since the initialization only ever happens once, just like in the current PR, you can't change it while it runs, but that was never a use case

@RalfJung

RalfJung commented Mar 10, 2020

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you can't change it while it runs, but that was never a use case

Yes it was, Miri does exactly that.

@oli-obk

oli-obk commented Mar 10, 2020

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That's OK, that happens before any error is ever thrown so the lazy in init hasn't happened yet

@RalfJung

RalfJung commented Mar 10, 2020•
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The intend is for that code to run after MIR got generated and const-eval happened. It gets called in after_analysis. That is why we delay the logger initialization in the first place, to log only Miri and not CTFE, to the extend possible.

Otherwise there'd be no reason for this entire init_early_loggers/init_late_loggers business, we'd just initialize everything early.

@oli-obk

oli-obk commented Mar 10, 2020

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Right. I guess let's do this for now and reconsider if/when someone dislikes it

RalfJung
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r=me with the doc nit fixed.

@wesleywiser
[Miri] Use a session variable instead of checking for an env var always
5357f83
In CTFE heavy code, checking the env var everytime is inefficient. We
can do a lot better by using a `Session` variable instead.
@wesleywiser
wesleywiserforce-pushed the miri_exception_env_var_to_session_var branch from ea85732 to 5357f83CompareMarch 10, 2020 22:18
@wesleywiser

wesleywiser commented Mar 11, 2020

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@bors r=RalfJung

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bors commented Mar 11, 2020

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📌 Commit 5357f83 has been approved by RalfJung

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bors commented Mar 11, 2020

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🌲 The tree is currently closed for pull requests below priority 1000, this pull request will be tested once the tree is reopened

@borsbors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 11, 2020
@CentrilCentril mentioned this pull request Mar 11, 2020
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bors added a commit that referenced this pull request Mar 11, 2020
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Auto merge of#69919- Centril:rollup-fxo33zs, r=Centril
c20d7ee
Rollup of 8 pull requests
Successful merges:
- #66472 (--show-coverage json)
- #69603 (tidy: replace `make check` with `./x.py test` in documentation)
- #69760 (Improve expression & attribute parsing)
- #69828 (fix memory leak when vec::IntoIter panics during drop)
- #69850 (panic_bounds_check: use caller_location, like PanicFnLangItem)
- #69876 (Add long error explanation for E0739)
- #69888 ([Miri] Use a session variable instead of checking for an env var always)
- #69893 (librustc_codegen_llvm: Use slices instead of 0-terminated strings)
Failed merges:
r? @ghost
@bors
bors merged commit b1471e0 into rust-lang:masterMar 11, 2020
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