Rust 1.59 rustc greatly increased compile time with include_str!

[sstangl]

The following repo/hash compiles with rustc v1.58, but loops forever in v1.59 and Nightly (1.61): sstangl/openpowerlifting@ac057e3

The problem appears to be with the compilation of a very small crate (modules/langpack) that uses include_str! to include some JSON files. The problematic method is the implementation of default():

    fn default() -> LangInfo {
        LangInfo {
            cz: json::from_str(include_str!("../translations/cz.json")).expect("cz"),
            de: json::from_str(include_str!("../translations/de.json")).expect("de"),
            el: json::from_str(include_str!("../translations/el.json")).expect("el"),
            en: json::from_str(include_str!("../translations/en.json")).expect("en"),
            eo: json::from_str(include_str!("../translations/eo.json")).expect("eo"),
            es: json::from_str(include_str!("../translations/es.json")).expect("es"),
            fi: json::from_str(include_str!("../translations/fi.json")).expect("fi"),
            fr: json::from_str(include_str!("../translations/fr.json")).expect("fr"),
            hr: json::from_str(include_str!("../translations/hr.json")).expect("hr"),
            hu: json::from_str(include_str!("../translations/hu.json")).expect("hu"),
            it: json::from_str(include_str!("../translations/it.json")).expect("it"),
            ja: json::from_str(include_str!("../translations/ja.json")).expect("ja"),
            ko: json::from_str(include_str!("../translations/ko.json")).expect("ko"),
            lt: json::from_str(include_str!("../translations/lt.json")).expect("lt"),
            nl: json::from_str(include_str!("../translations/nl.json")).expect("nl"),
            pl: json::from_str(include_str!("../translations/pl.json")).expect("pl"),
            pt: json::from_str(include_str!("../translations/pt.json")).expect("pt"),
            sk: json::from_str(include_str!("../translations/sk.json")).expect("sk"),
            sl: json::from_str(include_str!("../translations/sl.json")).expect("sl"),
            sr: json::from_str(include_str!("../translations/sr.json")).expect("sr"),
            sv: json::from_str(include_str!("../translations/sv.json")).expect("sv"),
            ru: json::from_str(include_str!("../translations/ru.json")).expect("ru"),
            tr: json::from_str(include_str!("../translations/tr.json")).expect("tr"),
            uk: json::from_str(include_str!("../translations/uk.json")).expect("uk"),
            vi: json::from_str(include_str!("../translations/vi.json")).expect("vi"),
            zh_hant: json::from_str(include_str!("../translations/zh-Hant.json")).expect("zh_hant"),
            zh_hans: json::from_str(include_str!("../translations/zh-Hans.json")).expect("zh_hans"),
        }
    }

When this function is removed, compilation succeeds.

GDB shows a thread stuck within LLVM, doing various optimizations, in a seemingly-endless loop (I waited several minutes. Previously this compilation with 1.58.1 took ~32s):

  6    Thread 0x7f6b9fbff640 (LWP 171415) "LTO langpack.a3" 0x00007f6bbeb4cd3f in llvm::SSAUpdater::GetValueAtEndOfBlockInternal(llvm::BasicBlock*) ()

  5    Thread 0x7f6ba03ff640 (LWP 171218) "opt langpack.a3" 0x00007f6bbe3f34cf in llvm::removeUnreachableBlocks(llvm::Function&, llvm::DomTreeUpdater*, llvm::MemorySSAUpdater*) ()

  5    Thread 0x7fa58c3ff640 (LWP 170073) "opt langpack.a3" 0x00007fa5aa4f21e4 in llvm::simplifyCFG(llvm::BasicBlock*, llvm::TargetTransformInfo const&, llvm::DomTreeUpdater*, llvm::SimplifyCFGOptions const&, llvm::ArrayRef<llvm::WeakVH>) ()

Steps to Reproduce

1. git clone https://github.com/sstangl/openpowerlifting.git
2. git checkout ac057e388ac911fda2e93acd8689d13f6df23034
3. cd modules/langpack
4. cargo build

Meta

rustc --version --verbose:

rustc 1.59.0 (9d1b2106e 2022-02-23)
binary: rustc
commit-hash: 9d1b2106e23b1abd32fce1f17267604a5102f57a
commit-date: 2022-02-23
host: x86_64-unknown-linux-gnu
release: 1.59.0
LLVM version: 13.0.0

The problem also exists with Nightly:

rustc 1.61.0-nightly (4b043faba 2022-02-24)
binary: rustc
commit-hash: 4b043faba34ccc053a4d0110634c323f6c03765e
commit-date: 2022-02-24
host: x86_64-unknown-linux-gnu
release: 1.61.0-nightly
LLVM version: 14.0.0

[MarkDDR]

From poking at the codebase a bit I have determined that include_str!() itself is not the direct cause of the issue, rather it is the optimizer at opt-level = 2 trying to optimize the serde_json::from_str::<Translations>() function given compile time knowledge of what the json string looks like. The issue also occurs if you manually inline the string

[MarkDDR]

I have created a much smaller code sample that recreates this bug https://github.com/MarkDDR/long_compile_rustc_1.59.0

[ehuss]

Thanks for putting together the reproductions! This seems to have started with #92419. cc @erikdesjardins

[erikdesjardins]

Presumably there are more issues with runaway inlining (possibly the same thing as #89524 / https://reviews.llvm.org/D98481 - serde almost certainly has mutual recursion somewhere).

It is unlikely that there will be a trivial fix, and I don't have time to investigate it deeply right now. I'll open a revert in a bit.

[nikic]

I looked into this a bit, and I'm not sure this qualifies as a catastrophic inlining issue. The input IR for "_ZN189_$LT$long_compile_time..big_struct.._..$LT$impl$u20$serde..de..Deserialize$u20$for$u20$long_compile_time..big_struct..BigStruct$GT$..deserialize..__Visitor$u20$as$u20$serde..de..Visitor$GT$9visit_map17h6f5c5ed07f452137E" is already more than 50k lines to start with and "only" grows to 140k lines during optimization. The result is huge because the input is huge.

Huge functions have a high chance of hitting one or the other super-linear optimization behavior in LLVM. I fixed one issue this hits in llvm/llvm-project@1dbeb64, which drops compile-time from 3:55 to 2:45.

I personally wouldn't block reapplication of the patch on this issue, as the interaction here is somewhat incidental -- large machine-generated code will always run into these sorts of issues, and minor perturbations in the generated code, rustc or LLVM can cause major variations in compile-time. Serde should avoid generating a large amount of code into a single function.