Replace all const evaluation with miri #46882

oli-obk · 2017-12-20T16:22:23Z

error reporting in constants prints a stacktrace through all called const fns
Trivial constant propagation and folding in MIR (always active, irrelevant of the optimization level)
can now use floating constants in patterns (previously only floating point literals were allowed)
- the future compat lint is still produced for both cases
can index into constant arrays during const eval (previously feature gated)
can create a constant union value with field a and read from field b
can dereference references into constants
can create references inside constants (const X: &u32 = &22)
Tuple struct constructors can be used in constants
regression in const eval errors spans (some of these need improvements in mir debug info)
can cast floats to ints and vice versa (in constants, and even nan/inf constants)
Mir dump prints false/true instead of 0u8/1u8
1i8 >> [8][0] does not lint about exceeding bitshifts anymore.
- Needs const propagation across projections
foo[I] produces a const eval lint if foo: [T; N] and N < I
- Essentially all builtin panics produce lints if they can be statically proven to trigger at runtime. This is on a best effort basis, so there might be some complex cases that don't trigger. (The runtime panic stays there, irrelevant of whether the lint is produced or not)
can use unions to implement transmute for Copy types in constants without a feature gate. With all the greatness and nasal demons that come with this.
can convert integers to &'static T in constants (useful for embedded)

fixes #34997 (stack overflow with many constants)
fixes #25574 (deref byte strings in patterns)
fixes #27918 (broken mir ICE)
fixes #46114 (ICE on struct constructors in patterns)
fixes #37448 (SomeStruct { foo } as SomeStruct)
fixes #43754 (return in const fn)
fixes #41898 (tuple struct constructors)
fixes #31364 (infinite recursion with const fn, fixed by miri's recursion limit)
closes #29947 (const indexing stabilization)
fixes #45044 (pattern matching repeat expressions)
fixes #47971 (ICE on const fn + references)
fixes #48081 (ICE on cyclic assoc const error)
fixes #48746 (nonhelpful error message with unions)

r? @eddyb

even though 1k loc are added in tests, this PR reduces the loc in this repository by 700

oli-obk · 2017-12-22T09:24:55Z

src/librustc_mir/hair/cx/expr.rs

+                value: cx.tcx().mk_const(ty::Const {
+                    val: if cx.tcx().sess.opts.debugging_opts.miri {
+                        let inst = ty::Instance::new(def_id, substs);
+                        let ptr = cx.tcx()


@eddyb help! I'm not sure where to start touching the hair in order to get these 'gcx and 'tcx lifetimes satisfied:

error[E0623]: lifetime mismatch --> src/librustc_mir/hair/cx/expr.rs:603:38 | 584 | fn method_callee<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>, | ------------------ this parameter and the return type are declared with different lifetimes... ... 587 | -> Expr<'tcx> { | ---------- ... 603 | let ptr = cx.tcx() | ^^^ ...but data from `cx` is returned here error: aborting due to previous error error: Could not compile `rustc_mir`.

bors · 2017-12-28T06:47:45Z

☔ The latest upstream changes (presumably #47018) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2017-12-28T10:29:28Z

☔ The latest upstream changes (presumably #47013) made this pull request unmergeable. Please resolve the merge conflicts.

alexreg · 2017-12-31T02:19:26Z

Great work on this, @oli-obk! I was just playing around with it myself, and was wondering on the state of it. Specifically, I seem to still be getting errors indicating that if expressions and loops are still not supported. Is this the case?

oli-obk · 2017-12-31T12:13:22Z

This PR does not enable much new stuff. That's not the point of it. We can enable more things after this PR. All I'm trying to do is to make it work on all code that worked before, without adding anything that we want to talk about in RFCs. That said, a few things will work after this PR.

Const indexing
Float patterns that go through constants (emitting the future compat lint about floats in patterns)
Dereferencing and referencing things in constants
Tuple struct construction in constants

Also I haven't pushed everything yet.

alexreg · 2017-12-31T15:35:56Z

@oli-obk Oh, I see. Thanks for the clarification.

alexcrichton · 2018-01-04T15:41:38Z

@oli-obk this is currently tagged as waiting-on-author, but did you want to start getting an early review?

alexreg · 2018-01-04T15:58:33Z

FWIW, @eddyb and I have been expanding on this significantly over the last few days. He's encouraging me to submit a PR, though I don't know if it's going to be against oli-obk's branch, or rust-lang:master.

bors · 2018-01-09T07:17:19Z

☔ The latest upstream changes (presumably #47276) made this pull request unmergeable. Please resolve the merge conflicts.

eddyb · 2018-01-09T23:07:12Z

src/librustc_trans/mir/constant.rs

        .expect("miri alloc not found");
    Ok(global_initializer(ccx, alloc))
 }

 impl<'a, 'tcx> MirContext<'a, 'tcx> {
    // Old version of trans_constant now used just for SIMD shuffle
-    pub fn remove_me__shuffle_indices(&mut self,
+    pub fn remove_me_shuffle_indices(&mut self,


LOL this wasn't a typo, I meant it to be an ugly name like that.

My bad. I got an error for non-snake-case names, and fixed it by removing the _ instead of adding a deny attribute. :-P

Ah if it triggered the lint then no worries! I didn't know it cared.

Yep, it's picky.

eddyb · 2018-01-15T00:24:01Z

Just wanted to note that 1. the PR description should include all changes 2. this will need a crater run.

oli-obk · 2018-01-15T09:56:41Z

I am now getting

thread 'rustc' panicked at 'Found unstable fingerprints for MirOptimized(main[317d]::main[0])', librustc/ty/maps/mod.rs:82:1

Which very likely results from the fact that AllocIds are generated on the fly when loading from the incremental cache, but we hash the AllocId's integer value. I can solve this by hashing the actual allocation, which obviously should never change. But there's an issue with that: Allocations can refer to themselves either directly or transitively. So hashing an allocation might require hashing the very same allocation, ....

Any clues how to solve this?

cc @nikomatsakis

oli-obk · 2018-01-15T10:56:28Z

cc @michaelwoerister

You removed the TyCtxt from StableHashingContext in d5b1fee#diff-c990dbfd90d57ef3911c819878ba7213
Is there any reason for this besides minimality?

I'm going to need access to the miri allocation interner to be able to hash AllocIds in a stable manner

michaelwoerister · 2018-01-15T11:54:24Z

@oli-obk, yes, we are creating StableHashingContexts before the TyCtxt is created:

rust/src/librustc_driver/driver.rs

Line 189 in 8ff449d

let hir_map = time(sess.time_passes(),

This could be solved by some refactoring, I think. @eddyb wanted to move HIR lowering to after the tcx is created a while ago.

There might also be another way of hashing AllocIds in a stable way? How are the integer ids generated? Are they in a "global address space" or per const?

eddyb · 2018-01-15T12:37:33Z

We could have an AllocId -> (ParamEnvAnd<GlobalId>, usize) mapping to record which evaluation an allocation came from, with an evaluation-local index.
Oh and you can use TLS_TCX to get around limitations with missing tcx.

oli-obk · 2018-01-15T13:45:00Z

During lowering we won't have any AllocIds. So I could simply add an Option<TyCtxt> to StableHashingContext.

Won't just hashing the ID be problematic if recompiling changes the value of a static?

michaelwoerister · 2018-01-15T13:53:15Z

Won't just hashing the ID be problematic if recompiling changes the value of a static?

That depends. Can you access the contents of an allocation via an AllocId directly? The contents of an allocation have to hashed at some point.

Is there a write up somewhere what these AllocIds are exactly?

oli-obk · 2018-01-15T13:58:12Z

Nope no writeup. I'll add one though

In short :

AllocIds are used to identify interned Allocations. Serialization serializes the allocation instead of the allocid and deserialization generates a new allocid on the fly to keep them unique

michaelwoerister · 2018-01-15T15:30:00Z

Is there one graph of allocations per ParamEnvAnd<GlobalId> that does not overlap with the graph of any other ParamEnvAnd<GlobalId>?

BatmanAoD · 2018-03-08T14:20:00Z

🎆 Wooooo! Congratulations, everyone!

bdrewery · 2018-03-09T22:16:06Z

Getting a weird build crash on FreeBSD after this merge #48888

(This was buggy before rust-lang#46882)

Correct a few stability attributes * `const_indexing` language feature was stabilized in 1.26.0 by #46882 * `Display` impls for `PanicInfo` and `Location` were stabilized in 1.26.0 by #47687 * `TrustedLen` is still unstable so its impls should be as well even though `RangeInclusive` was stabilized by #47813 * `!Send` and `!Sync` for `Args` and `ArgsOs` were stabilized in 1.26.0 by #48005 * `EscapeDefault` has been stable since 1.0.0 so should continue to show that even though it was moved to core in #48735 This could be backported to beta like #49612

ur0 · 2018-04-16T05:25:00Z

I'm sorry if this isn't the right place, but are tuple struct constructors available in the latest stable build (2018-03-25)?

oli-obk · 2018-04-16T05:38:33Z

This is as good a place as any other ;)

No they're not in the current stable. they'll be in the next stable (so they are in the current beta)

rust-highfive assigned eddyb Dec 20, 2017

kennytm added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 20, 2017

oli-obk changed the title ~~WIP: add more boosters to miri...~~ WIP: add more boosters 🚀 to miri... Dec 21, 2017

oli-obk force-pushed the miri3 branch 2 times, most recently from 7de6a56 to ef9043b Compare December 22, 2017 09:23

oli-obk commented Dec 22, 2017

View reviewed changes

oli-obk force-pushed the miri3 branch from f3fe013 to d7928a1 Compare December 28, 2017 01:15

oli-obk force-pushed the miri3 branch from 9cb239a to 625820f Compare December 28, 2017 09:47

oli-obk force-pushed the miri3 branch from d07e8e6 to 3fac474 Compare January 8, 2018 10:38

oli-obk force-pushed the miri3 branch from a199c77 to d10b896 Compare January 9, 2018 19:20

eddyb reviewed Jan 9, 2018

View reviewed changes

oli-obk force-pushed the miri3 branch from 5fd4cb8 to 38023e4 Compare January 14, 2018 12:13

oli-obk changed the title ~~WIP: add more boosters 🚀 to miri...~~ WIP: Replace all const evaluation with miri Jan 15, 2018

bdrewery mentioned this pull request Mar 9, 2018

Crash building libstd on FreeBSD after miri const eval changes. #48888

Closed

This was referenced Mar 10, 2018

Missing index out of bounds error #48920

Closed

Compiling with -C debuginfo=2 reduces warnings unexpectedly #48900

Closed

alexcrichton mentioned this pull request Mar 15, 2018

ICE during cross-compilation and const eval #49033

Closed

EpicatSupercell mentioned this pull request Mar 15, 2018

clippy_lints-0.0.187 error breaks +nightly clippy install rust-lang/rust-clippy#2532

Closed

oli-obk mentioned this pull request Mar 16, 2018

Non-capturing closures in statics #44669

Closed

SimonSapin added a commit to SimonSapin/rust that referenced this pull request Mar 17, 2018

Test NonZero in a const item in a pattern.

7cf1f18

(This was buggy before rust-lang#46882)

solson mentioned this pull request Mar 20, 2018

upstream to rustc rust-lang/miri#105

Closed

eira-fransham mentioned this pull request Mar 20, 2018

All fixed-size array impls show up as <unevaluated[]> #49208

Closed

pnkfelix mentioned this pull request Mar 21, 2018

Compiler panic: unexpected unsized tail: TyProjection(ProjectionTy { substs: Slice([chrono::Utc]), ... #48336

Closed

ollie27 mentioned this pull request Apr 5, 2018

Correct a few stability attributes #49673

Merged

XAMPPRocky mentioned this pull request May 4, 2018

Update RELEASES.md for 1.26.0 #49523

Merged

kennytm mentioned this pull request May 16, 2018

NaN > NaN returns true #50811

Closed

compiler-errors mentioned this pull request Jan 30, 2022

ICE on match of const variables: destructure_const #93470

Closed

bjorn3 mentioned this pull request Sep 23, 2022

Miri subtree instructions rust-lang/miri#2561

Closed

GrigorenkoPV mentioned this pull request Mar 26, 2024

ICE: !base.layout().is_sized() #123078

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Replace all const evaluation with miri #46882

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Replace all const evaluation with miri #46882

Replace all const evaluation with miri #46882

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