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2025-07-16use `codegen_instance_attrs` where an instance is (easily) availableFolkert de Vries-2/+2
2025-07-16add `codegen_instance_attrs` queryFolkert de Vries-6/+2
and use it for naked functions
2025-07-16fix `-Zsanitizer=kcfi` on `#[naked]` functionsFolkert de Vries-2/+6
And more broadly only codegen `InstanceKind::Item` using the naked function codegen code. Other instance kinds should follow the normal path.
2025-07-09Add opaque TypeId handles for CTFEOli Scherer-0/+13
2025-07-07compiler: Parse `p-` specs in datalayout string, allow definition of custom ↵Edoardo Marangoni-4/+4
default data address space
2025-07-03Make __rust_alloc_error_handler_should_panic a functionDaniel Paoliello-13/+28
2025-07-01Remove support for dyn*Michael Goulet-149/+14
2025-06-30Rollup merge of #143140 - RalfJung:ptr-into-parts, r=oli-obkMatthias Krüger-1/+1
give Pointer::into_parts a more scary name and offer a safer alternative `into_parts` is a bit too innocent of a name for a somewhat subtle operation. r? `@oli-obk`
2025-06-30Stop backends from needing to support nullary intrinsicsOli Scherer-15/+0
2025-06-29Rollup merge of #142078 - sayantn:more-intrinsics, r=workingjubileeGuillaume Gomez-1/+4
Add SIMD funnel shift and round-to-even intrinsics This PR adds 3 new SIMD intrinsics - `simd_funnel_shl` - funnel shift left - `simd_funnel_shr` - funnel shift right - `simd_round_ties_even` (vector version of `round_ties_even_fN`) TODO (future PR): implement `simd_fsh{l,r}` in miri, cg_gcc and cg_clif (it is surprisingly hard to implement without branches, the common tricks that rotate uses doesn't work because we have 2 elements now. e.g, the `-n&31` trick used by cg_gcc to implement rotate doesn't work with this because then `fshl(a, b, 0)` will be `a | b`) [#t-compiler > More SIMD intrinsics](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/More.20SIMD.20intrinsics/with/522130286) `@rustbot` label T-compiler T-libs A-intrinsics F-core_intrinsics r? `@workingjubilee`
2025-06-29give Pointer::into_parts a more scary name and offer a safer alternativeRalf Jung-1/+1
2025-06-28Auto merge of #141759 - 1c3t3a:discriminants-query, r=saethlinbors-0/+12
Insert checks for enum discriminants when debug assertions are enabled Similar to the existing null-pointer and alignment checks, this checks for valid enum discriminants on creation of enums through unsafe transmutes. Essentially this sanitizes patterns like the following: ```rust let val: MyEnum = unsafe { std::mem::transmute<u32, MyEnum>(42) }; ``` An extension of this check will be done in a follow-up that explicitly sanitizes for extern enum values that come into Rust from e.g. C/C++. This check is similar to Miri's capabilities of checking for valid construction of enum values. This PR is inspired by saethlin@'s PR https://github.com/rust-lang/rust/pull/104862. Thank you so much for keeping this code up and the detailed comments! I also pair-programmed large parts of this together with vabr-g@. r? `@saethlin`
2025-06-27Insert checks for enum discriminants when debug assertions are enabledBastian Kersting-0/+12
Similar to the existing nullpointer and alignment checks, this checks for valid enum discriminants on creation of enums through unsafe transmutes. Essentially this sanitizes patterns like the following: ```rust let val: MyEnum = unsafe { std::mem::transmute<u32, MyEnum>(42) }; ``` An extension of this check will be done in a follow-up that explicitly sanitizes for extern enum values that come into Rust from e.g. C/C++. This check is similar to Miri's capabilities of checking for valid construction of enum values. This PR is inspired by saethlin@'s PR https://github.com/rust-lang/rust/pull/104862. Thank you so much for keeping this code up and the detailed comments! I also pair-programmed large parts of this together with vabr-g@.
2025-06-24Merge commit '8c848e0604b5d26fad120914f822f564fe05c52a' into ↵bjorn3-7/+9
sync_cg_clif-2025-06-24
2025-06-22cranelift: fix target feature name type: "fxsr"Martin Liska-1/+1
2025-06-18Auto merge of #141061 - dpaoliello:shimasfn, r=bjorn3bors-12/+28
Change __rust_no_alloc_shim_is_unstable to be a function This fixes a long sequence of issues: 1. A customer reported that building for Arm64EC was broken: #138541 2. This was caused by a bug in my original implementation of Arm64EC support, namely that only functions on Arm64EC need to be decorated with `#` but Rust was decorating statics as well. 3. Once I corrected Rust to only decorate functions, I started linking failures where the linker couldn't find statics exported by dylib dependencies. This was caused by the compiler not marking exported statics in the generated DEF file with `DATA`, thus they were being exported as functions not data. 4. Once I corrected the way that the DEF files were being emitted, the linker started failing saying that it couldn't find `__rust_no_alloc_shim_is_unstable`. This is because the MSVC linker requires the declarations of statics imported from other dylibs to be marked with `dllimport` (whereas it will happily link to functions imported from other dylibs whether they are marked `dllimport` or not). 5. I then made a change to ensure that `__rust_no_alloc_shim_is_unstable` was marked as `dllimport`, but the MSVC linker started emitting warnings that `__rust_no_alloc_shim_is_unstable` was marked as `dllimport` but was declared in an obj file. This is a harmless warning which is a performance hint: anything that's marked `dllimport` must be indirected via an `__imp` symbol so I added a linker arg in the target to suppress the warning. 6. A customer then reported a similar warning when using `lld-link` (<https://github.com/rust-lang/rust/pull/140176#issuecomment-2872448443>). I don't think it was an implementation difference between the two linkers but rather that, depending on the obj that the declaration versus uses of `__rust_no_alloc_shim_is_unstable` landed in we would get different warnings, so I suppressed that warning as well: #140954. 7. Another customer reported that they weren't using the Rust compiler to invoke the linker, thus these warnings were breaking their build: <https://github.com/rust-lang/rust/pull/140176#issuecomment-2881867433>. At that point, my original change was reverted (#141024) leaving Arm64EC broken yet again. Taking a step back, a lot of these linker issues arise from the fact that `__rust_no_alloc_shim_is_unstable` is marked as `extern "Rust"` in the standard library and, therefore, assumed to be a foreign item from a different crate BUT the Rust compiler may choose to generate it either in the current crate, some other crate that will be statically linked in OR some other crate that will by dynamically imported. Worse yet, it is impossible while building a given crate to know if `__rust_no_alloc_shim_is_unstable` will statically linked or dynamically imported: it might be that one of its dependent crates is the one with an allocator kind set and thus that crate (which is compiled later) will decide depending if it has any dylib dependencies or not to import `__rust_no_alloc_shim_is_unstable` or generate it. Thus, there is no way to know if the declaration of `__rust_no_alloc_shim_is_unstable` should be marked with `dllimport` or not. There is a simple fix for all this: there is no reason `__rust_no_alloc_shim_is_unstable` must be a static. It needs to be some symbol that must be linked in; thus, it could easily be a function instead. As a function, there is no need to mark it as `dllimport` when dynamically imported which avoids the entire mess above. There may be a perf hit for changing the `volatile load` to be a `tail call`, so I'm happy to change that part back (although I question what the codegen of a `volatile load` would look like, and if the backend is going to try to use load-acquire semantics). Build with this change applied BEFORE #140176 was reverted to demonstrate that there are no linking issues with either MSVC or MinGW: <https://github.com/rust-lang/rust/actions/runs/15078657205> Incidentally, I fixed `tests/run-make/no-alloc-shim` to work with MSVC as I needed it to be able to test locally (FYI for #128602) r? `@bjorn3` cc `@jieyouxu`
2025-06-16Change __rust_no_alloc_shim_is_unstable to be a functionDaniel Paoliello-12/+28
2025-06-16Fix RISC-V C function ABI when passing/returning structs containing floatsbeetrees-24/+42
2025-06-15Rollup merge of #142389 - beetrees:cranelift-arg-ext, r=bjorn3León Orell Valerian Liehr-22/+37
Apply ABI attributes on return types in `rustc_codegen_cranelift` - The [x86-64 System V ABI standard](https://gitlab.com/x86-psABIs/x86-64-ABI/-/jobs/artifacts/master/raw/x86-64-ABI/abi.pdf?job=build) doesn't sign/zero-extend integer arguments or return types. - But the de-facto standard as implemented by Clang and GCC is to sign/zero-extend arguments to 32 bits (but not return types). - Additionally, Apple targets [sign/zero-extend both arguments and return values to 32 bits](https://developer.apple.com/documentation/xcode/writing-64-bit-intel-code-for-apple-platforms#Pass-arguments-to-functions-correctly). - However, the `rustc_target` ABI adjustment code currently [unconditionally extends both arguments and return values to 32 bits](https://github.com/rust-lang/rust/blame/e703dff8fe220b78195c53478e83fb2f68d8499c/compiler/rustc_target/src/callconv/x86_64.rs#L240) on all targets. - This doesn't cause a miscompilation when compiling with LLVM as LLVM will ignore the `signext`/`zeroext` attribute when applied to return types on non-Apple x86-64 targets. - Cranelift, however, does not have a similar special case, requiring `rustc` to set the argument extension attribute correctly. - However, `rustc_codegen_cranelift` doesn't currently apply ABI attributes to return types at all, meaning `rustc_codegen_cranelift` will currently miscompile `i8`/`u8`/`i16`/`u16` returns on x86-64 Apple targets as those targets require sign/zero-extension of return types. This PR fixes the bug(s) by making the `rustc_target` x86-64 System V ABI only mark return types as sign/zero-extended on Apple platforms, while also making `rustc_codegen_cranelift` apply ABI attributes to return types. The RISC-V and s390x C ABIs also require sign/zero extension of return types, so this will fix those targets when building with `rustc_codegen_cranelift` too. r? `````@bjorn3`````
2025-06-15Rollup merge of #141769 - bjorn3:codegen_metadata_module_rework, ↵León Orell Valerian Liehr-62/+3
r=workingjubilee,saethlin Move metadata object generation for dylibs to the linker code This deduplicates some code between codegen backends and may in the future allow adding extra metadata that is only known at link time. Prerequisite of https://github.com/rust-lang/rust/issues/96708.
2025-06-15Implement `simd_round_ties_even` for miri, cg_clif and cg_gccsayantn-1/+4
2025-06-13Auto merge of #142443 - matthiaskrgr:rollup-l1l6d0v, r=matthiaskrgrbors-0/+5
Rollup of 9 pull requests Successful merges: - rust-lang/rust#128425 (Make `missing_fragment_specifier` an unconditional error) - rust-lang/rust#135927 (retpoline and retpoline-external-thunk flags (target modifiers) to enable retpoline-related target features) - rust-lang/rust#140770 (add `extern "custom"` functions) - rust-lang/rust#142176 (tests: Split dont-shuffle-bswaps along opt-levels and arches) - rust-lang/rust#142248 (Add supported asm types for LoongArch32) - rust-lang/rust#142267 (assert more in release in `rustc_ast_lowering`) - rust-lang/rust#142274 (Update the stdarch submodule) - rust-lang/rust#142276 (Update dependencies in `library/Cargo.lock`) - rust-lang/rust#142308 (Upgrade `object`, `addr2line`, and `unwinding` in the standard library) Failed merges: - rust-lang/rust#140920 (Extract some shared code from codegen backend target feature handling) r? `@ghost` `@rustbot` modify labels: rollup try-job: aarch64-apple try-job: x86_64-msvc-1 try-job: x86_64-gnu try-job: dist-i586-gnu-i586-i686-musl try-job: test-various
2025-06-12add `extern "custom"` functionsFolkert de Vries-0/+5
2025-06-12intrinsics: rename min_align_of to align_ofRalf Jung-4/+4
2025-06-12Apply ABI attributes on return types in `rustc_codegen_cranelift`beetrees-22/+37
2025-06-08Remove rustc's notion of "preferred" alignment AKA `__alignof`Jubilee Young-5/+1
In PR 90877 T-lang decided not to remove `intrinsics::pref_align_of`. However, the intrinsic and its supporting code 1. is a nightly feature, so can be removed at compiler/libs discretion 2. requires considerable effort in the compiler to support, as it necessarily complicates every single site reasoning about alignment 3. has been justified based on relevance to codegen, but it is only a requirement for C++ (not C, not Rust) stack frame layout for AIX, in ways Rust would not consider even with increased C++ interop 4. is only used by rustc to overalign some globals, not correctness 5. can be adequately replaced by other rules for globals, as it mostly affects alignments for a few types under 16 bytes of alignment 6. has only one clear benefactor: automating C -> Rust translation for GNU extensions like `__alignof` 7. such code was likely intended to be `alignof` or `_Alignof`, because the GNU extension is a "false friend" of the C keyword, which makes the choice to support such a mapping very questionable 8. makes it easy to do incorrect codegen in the compiler by its mere presence as usual Rust rules of alignment (e.g. `size == align * N`) do not hold with preferred alignment The implementation is clearly damaging the code quality of the compiler. Thus it is within the compiler team's purview to simply rip it out. If T-lang wishes to have this intrinsic restored for c2rust's benefit, it would have to use a radically different implementation that somehow does not cause internal incorrectness. Until then, remove the intrinsic and its supporting code, as one tool and an ill-considered GCC extension cannot justify risking correctness. Because we touch a fair amount of the compiler to change this at all, and unfortunately the duplication of AbiAndPrefAlign is deep-rooted, we keep an "AbiAlign" type which we can wean code off later.
2025-06-07intrinsics: use const generic to set atomic orderingRalf Jung-15/+13
2025-06-07Auto merge of #141964 - sayantn:update-stdarch, r=Amanieubors-8/+8
Update stdarch submodule Updates the stdarch submodule. ## Merged PRs - rust-lang/stdarch#1797 - rust-lang/stdarch#1758 - rust-lang/stdarch#1798 - rust-lang/stdarch#1811 - rust-lang/stdarch#1810 - rust-lang/stdarch#1807 - rust-lang/stdarch#1806 - rust-lang/stdarch#1812 - rust-lang/stdarch#1795 - rust-lang/stdarch#1796 - rust-lang/stdarch#1813 - rust-lang/stdarch#1816 - rust-lang/stdarch#1818 - rust-lang/stdarch#1820 - rust-lang/stdarch#1819 r? `@Amanieu` `@rustbot` label T-libs-api Closes rust-lang/rust#111137
2025-06-06Rollup merge of #142103 - scottmcm:fieldidx-in-interp, r=oli-obkGuillaume Gomez-4/+3
Update `InterpCx::project_field` to take `FieldIdx` As suggested by Ralf in https://github.com/rust-lang/rust/pull/142005#discussion_r2125839015
2025-06-05Update `InterpCx::project_field` to take `FieldIdx`Scott McMurray-4/+3
As suggested by Ralf in 142005.
2025-06-05Replace some `Option<Span>` with `Span` and use DUMMY_SP instead of NoneOli Scherer-18/+18
2025-06-03Change `tag_field` to `FieldIdx` in `Variants::Multiple`Scott McMurray-3/+3
It was already available as a generic parameter anyway, and it's not like we'll ever put a tag in the 5-billionth field.
2025-06-03Rollup merge of #141569 - workingjubilee:canonicalize-abi, r=bjorn3Matthias Krüger-27/+22
Replace ad-hoc ABI "adjustments" with an `AbiMap` to `CanonAbi` Our `conv_from_spec_abi`, `adjust_abi`, and `is_abi_supported` combine to give us a very confusing way of reasoning about what _actual_ calling convention we want to lower our code to and whether we want to compile the resulting code at all. Instead of leaving this code as a miniature adventure game in which someone tries to combine stateful mutations into a Rube Goldberg machine that will let them escape the maze and arrive at the promised land of codegen, we let `AbiMap` devour this complexity. Once you have an `AbiMap`, you can answer which `ExternAbi`s will lower to what `CanonAbi`s (and whether they will lower at all). Removed: - `conv_from_spec_abi` replaced by `AbiMap::canonize_abi` - `adjust_abi` replaced by same - `Conv::PreserveAll` as unused - `Conv::Cold` as unused - `enum Conv` replaced by `enum CanonAbi` target-spec.json changes: - If you have a target-spec.json then now your "entry-abi" key will be specified in terms of one of the `"{abi}"` strings Rust recognizes, e.g. ```json "entry-abi": "C", "entry-abi": "win64", "entry-abi": "aapcs", ```
2025-06-03cg_clif: convert to CanonAbiJubilee Young-27/+22
2025-06-03Add impl for `llvm.roundeven` in cg_clifsayantn-8/+8
- remove unused `llvm.aarch64.neon.frintn` from cg_clif
2025-06-03Move metadata object generation for dylibs to the linker codebjorn3-48/+3
This deduplicates some code between codegen backends and may in the future allow adding extra metadata that is only known at link time.
2025-06-03Only borrow EncodedMetadata in codegen_cratebjorn3-18/+4
And move passing it to the linker to the driver code.
2025-05-28atomic_load intrinsic: use const generic parameter for orderingRalf Jung-1/+2
2025-05-25Merge commit '979dcf8e2f213e4f4b645cb62e7fe9f4f2c0c785' into ↵bjorn3-198/+994
sync_cg_clif-2025-05-25
2025-05-09Use intrinsics for `{f16,f32,f64,f128}::{minimum,maximum}` operationsUrgau-0/+37
2025-05-05Rename Instance::new to Instance::new_raw and add a note that it is rawMichael Goulet-1/+1
2025-04-30Rollup merge of #134232 - bjorn3:naked_asm_improvements, r=wesleywiserMatthias Krüger-289/+200
Share the naked asm impl between cg_ssa and cg_clif This was introduced in https://github.com/rust-lang/rust/pull/128004.
2025-04-30Fix naked asm symbol name for cg_clif on macOSbjorn3-1/+2
2025-04-28Rollup merge of #140323 - tgross35:cfg-unstable-float, r=UrgauChris Denton-3/+12
Implement the internal feature `cfg_target_has_reliable_f16_f128` Support for `f16` and `f128` is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable. Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which provides the following new configuration gates: * `cfg(target_has_reliable_f16)` * `cfg(target_has_reliable_f16_math)` * `cfg(target_has_reliable_f128)` * `cfg(target_has_reliable_f128_math)` `reliable_f16` and `reliable_f128` indicate that basic arithmetic for the type works correctly. The `_math` versions indicate that anything relying on `libm` works correctly, since sometimes this hits a separate class of codegen bugs. These options match configuration set by the build script at [1]. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up. The config introduced here is not planned to ever become stable, it is only intended to replace the build scripts for `std` tests and `compiler-builtins` that don't have any way to configure based on the codegen backend. MCP: https://github.com/rust-lang/compiler-team/issues/866 Closes: https://github.com/rust-lang/compiler-team/issues/866 [1]: https://github.com/rust-lang/rust/blob/555e1d0386f024a8359645c3217f4b3eae9be042/library/std/build.rs#L84-L186 --- The second commit makes use of this config to replace `cfg_{f16,f128}{,_math}` in `library/`. I omitted providing a `cfg(bootstrap)` configuration to keep things simpler since the next beta branch is in two weeks. try-job: aarch64-gnu try-job: i686-msvc-1 try-job: test-various try-job: x86_64-gnu try-job: x86_64-msvc-ext2
2025-04-28AsyncDrop implementation using shim codegen of ↵Andrew Zhogin-5/+10
async_drop_in_place::{closure}, scoped async drop added.
2025-04-27Implement the internal feature `cfg_target_has_reliable_f16_f128`Trevor Gross-3/+12
Support for `f16` and `f128` is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable. Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which provides the following new configuration gates: * `cfg(target_has_reliable_f16)` * `cfg(target_has_reliable_f16_math)` * `cfg(target_has_reliable_f128)` * `cfg(target_has_reliable_f128_math)` `reliable_f16` and `reliable_f128` indicate that basic arithmetic for the type works correctly. The `_math` versions indicate that anything relying on `libm` works correctly, since sometimes this hits a separate class of codegen bugs. These options match configuration set by the build script at [1]. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up. The config introduced here is not planned to ever become stable, it is only intended to replace the build scripts for `std` tests and `compiler-builtins` that don't have any way to configure based on the codegen backend. MCP: https://github.com/rust-lang/compiler-team/issues/866 Closes: https://github.com/rust-lang/compiler-team/issues/866 [1]: https://github.com/rust-lang/rust/blob/555e1d0386f024a8359645c3217f4b3eae9be042/library/std/build.rs#L84-L186
2025-04-14Share part of the global_asm!() implementation between cg_ssa and cg_clifbjorn3-69/+4
2025-04-14Use cg_ssa's version of codegen_naked_asm in cg_clifbjorn3-283/+258
2025-04-14Move `has_self` field to `hir::AssocKind::Fn`.Nicholas Nethercote-2/+2
`hir::AssocItem` currently has a boolean `fn_has_self_parameter` field, which is misplaced, because it's only relevant for associated fns, not for associated consts or types. This commit moves it (and renames it) to the `AssocKind::Fn` variant, where it belongs. This requires introducing a new C-style enum, `AssocTag`, which is like `AssocKind` but without the fields. This is because `AssocKind` values are passed to various functions like `find_by_ident_and_kind` to indicate what kind of associated item should be searched for, and having to specify `has_self` isn't relevant there. New methods: - Predicates `AssocItem::is_fn` and `AssocItem::is_method`. - `AssocItem::as_tag` which converts `AssocItem::kind` to `AssocTag`. Removed `find_by_name_and_kinds`, which is unused. `AssocItem::descr` can now distinguish between methods and associated functions, which slightly improves some error messages.
2025-04-11Auto merge of #139453 - compiler-errors:incr, r=jieyouxubors-19/+35
Prepend temp files with per-invocation random string to avoid temp filename conflicts https://github.com/rust-lang/rust/issues/139407 uncovered a very subtle unsoundness with incremental codegen, failing compilation sessions (due to assembler errors), and the "prefer hard linking over copying files" strategy we use in the compiler for file management. Specifically, imagine we're building a single file 3 times, all with `-Csave-temps -Cincremental=...`. Let's call the object file we're building for the codegen unit for `main` "`XXX.o`" just for clarity since it's probably some gigantic hash name: ``` #[inline(never)] #[cfg(any(rpass1, rpass3))] fn a() -> i32 { 0 } #[cfg(any(cfail2))] fn a() -> i32 { 1 } fn main() { evil::evil(); assert_eq!(a(), 0); } mod evil { #[cfg(any(rpass1, rpass3))] pub fn evil() { unsafe { std::arch::asm!("/* */"); } } #[cfg(any(cfail2))] pub fn evil() { unsafe { std::arch::asm!("missing"); } } } ``` Session 1 (`rpass1`): * Type-check, borrow-check, etc. * Serialize the dep graph to the incremental working directory `.../s-...-working/`. * Codegen object file to a temp file `XXX.rcgu.o` which is spit out in the cwd. * Hard-link[^1] `XXX.rcgu.o` to the incremental working directory `.../s-...-working/XXX.o`. * Save-temps option means we don't delete `XXX.rgcu.o`. * Link the binary and stuff. * Finalize[^2] the working incremental session by renaming `.../s-...-working` to ` s-...-asjkdhsjakd` (some other finalized incr comp session dir name). Session 2 (`cfail2`): * Load artifacts from the previous *finalized* incremental session, namely the dep graph. * Type-check, borrow-check, etc. since the file has changed, so most dep graph nodes are red. * Serialize the dep graph to the incremental working directory `.../s-...-working/`. * Codegen object file to a temp file `XXX.rcgu.o`. **HERE IS THE PROBLEM**: The hard-link is still set up to point to the inode from `XXX.o` from the first session, so this also modifies the `XXX.o` in the previous finalized session directory. * Codegen emits an error b/c `missing` is not an instruction, so we abort before finalizing the incremental session. Specifically, this means that the *previous* session is the last finalized session. Session 3 (`rpass3`): * Load artifacts from the previous *finalized* incremental session, namely the dep graph. NOTE that this is from session 1. * All the dep graph nodes are green since we are basically replaying session 1. * codegen object file `XXX.o`, which is detected as *reused* from session 1 since dep nodes were green. That means we **reuse** `XXX.o` which had been dirtied from session 2. * Link the binary and stuff. This results in a binary which reuses some of the build artifacts from session 2, but thinks it's from session 1. At this point, I hope it's clear to see that the incremental results from session 1 were dirtied from session 2, but we reuse them as if session 1 was the previous (finalized) incremental session we ran. This is at best really buggy, and at worst **unsound**. This isn't limited to `-C save-temps`, since there are other combinations of flags that may keep around temporary files (hard linked) in the working directory (like `-C debuginfo=1 -C split-debuginfo=unpacked` on darwin, for example). --- This PR implements a fix which is to prepend temp filenames with a random string that is generated per invocation of rustc. This string is not *deterministic*, but temporary files are transient anyways, so I don't believe this is a problem. That means that temp files are now something like... `{crate-name}.{cgu}.{invocation_temp}.rcgu.o`, where `{invocation_temp}` is the new temporary string we generate per invocation of rustc. Fixes https://github.com/rust-lang/rust/issues/139407 [^1]: https://github.com/rust-lang/rust/blob/175dcc7773d65c1b1542c351392080f48c05799f/compiler/rustc_fs_util/src/lib.rs#L60 [^2]: https://github.com/rust-lang/rust/blob/175dcc7773d65c1b1542c351392080f48c05799f/compiler/rustc_incremental/src/persist/fs.rs#L1-L40