Type fallback refactorings by WaffleLapkin · Pull Request #159026 · rust-lang/rust

WaffleLapkin · 2026-07-09T16:32:06Z

View all comments

r? types

Don't merge different kinds of infer variables into Ty before matching them back
Do fallback only on root vars (this is semantically equivalent to what we currently do; unifying any of the infer vars from the same equivalence class necesserily affects all of them) (this makes Implement "low priority impls" #159003 a bit less hacky though)
Do some simplification that has been allowed by the previous changes

cc @lcnr

WaffleLapkin · 2026-07-09T19:12:45Z

@bors try @rust-timer queue

Type fallback refactorings

rust-bors · 2026-07-09T21:19:26Z

☀️ Try build successful (CI)
Build commit: 6a25a06 (6a25a0621d4f43872d80fc0aba25c7aedfc92c0f)
Base parent: 3664b37 (3664b37017c529cad0f0ed259769f15743c21a6a)

rust-timer · 2026-07-10T00:52:33Z

Finished benchmarking commit (6a25a06): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.2%, 0.3%]	4
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.3%, -2.0%]	12
All ❌✅ (primary)	0.2%	[0.2%, 0.3%]	4

Max RSS (memory usage)

Results (primary 3.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.4%	[2.6%, 4.1%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.4%	[2.6%, 4.1%]	2

Cycles

Results (secondary -5.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.3%	[-14.7%, -2.8%]	7
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.1%]	59
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	22
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	59

Bootstrap: 487.967s -> 488.861s (0.18%)
Artifact size: 388.37 MiB -> 388.42 MiB (0.01%)

WaffleLapkin · 2026-07-14T12:30:22Z

I think the perf regression is noise.
@rustbot label: +perf-regression-triaged

lcnr · 2026-07-21T08:31:16Z

            .map(|&ty_id| self.shallow_resolve(Ty::new_var(self.tcx, ty_id)))
            .filter_map(|ty| ty.ty_vid())
            .map(|vid| self.root_var(vid))


that should also be a probe_with_root_vid i think? seems like a very cumbersome way to get the root vid of a ty var

View changes since the review

The problem is that everything to do with type variables is private. See 680fc04 for what needs to be made public.

lcnr · 2026-07-21T08:34:38Z

unsure about the last commit after applying my other review comments, but r=me after nits on the other changes

WaffleLapkin · 2026-08-05T09:33:17Z

@bors r=lcnr

(see #159026 (comment); I've also applied suggestion from #159026 (comment))

rust-bors · 2026-08-05T09:33:21Z

📌 Commit 4ac3cec has been approved by lcnr

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 10. This pull request will be tested once the tree is reopened.

Reason for tree closure: manually handling queue due to backlog

@lcnr

Type fallback refactorings - Don't merge different kinds of infer variables into `Ty` before matching them back - Do fallback only on root vars (this is semantically equivalent to what we currently do; unifying any of the infer vars from the same equivalence class necesserily affects all of them) (this makes #159003 a bit less hacky though) - Do some simplification that has been allowed by the previous changes cc @lcnr

rust-bors · 2026-08-05T11:26:30Z

💔 Test for 9495eda failed: CI. Failed job:

auto - x86_64-gnu-tools (web logs, enhanced plaintext logs)

JonathanBrouwer · 2026-08-05T11:28:03Z

@bors retry

rust-log-analyzer · 2026-08-05T11:30:40Z

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

..............F..............................      (145/145)

======== tests/rustdoc-gui/sidebar.goml ========

[ERROR] line 208: `#sidebar-button a` not found: for command `assert-css: ("#sidebar-button a::before", {"content": |image_url|})`
    at <file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/src/huge_logo/lib.rs.html#2-17>


<= doc-ui tests done: 144 succeeded, 1 failed, 0 filtered out

Error: ()

rust-log-analyzer · 2026-08-05T12:36:24Z

The job optional-x86_64-gnu-autodiff failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)


---- [codegen] tests/codegen-llvm/autodiff/abi_handling.rs#debug stdout ----
------rustc stdout------------------------------

------rustc stderr------------------------------
rustc: /checkout/src/llvm-project/llvm/include/llvm/ADT/APInt.h:127: llvm::APInt::APInt(unsigned int, uint64_t, bool, bool): Assertion `llvm::isUIntN(BitWidth, val) && "Value is not an N-bit unsigned value"' failed.

------------------------------------------

error in revision `debug`: compilation failed!
status: signal: 6 (SIGABRT) (core dumped)
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/codegen-llvm/autodiff/abi_handling.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--cfg" "debug" "--check-cfg" "cfg(test,FALSE,debug,release)" "-O" "-Cdebug-assertions=no" "-Zcodegen-source-order" "--emit" "llvm-ir" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/autodiff/abi_handling.debug/abi_handling.ll" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Zautodiff=Enable,NoTT" "-C" "opt-level=0" "-Clto=fat"
stdout: none
--- stderr -------------------------------
rustc: /checkout/src/llvm-project/llvm/include/llvm/ADT/APInt.h:127: llvm::APInt::APInt(unsigned int, uint64_t, bool, bool): Assertion `llvm::isUIntN(BitWidth, val) && "Value is not an N-bit unsigned value"' failed.
------------------------------------------

---- [codegen] tests/codegen-llvm/autodiff/abi_handling.rs#debug stdout end ----

failures:
---
failures:

---- [ui] tests/ui/autodiff/incremental.rs#DEBUG stdout ----

error in revision `DEBUG`: test compilation failed although it shouldn't!
status: signal: 6 (SIGABRT) (core dumped)
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/autodiff/incremental.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--cfg" "debug" "--check-cfg" "cfg(test,FALSE,debug,release)" "-C" "incremental=/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/autodiff/incremental.DEBUG/incremental.inc" "-Z" "incremental-verify-ich" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/autodiff/incremental.DEBUG" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-Zautodiff=Enable,NoTT" "-Copt-level=0" "-Clto=fat" "-Cdebuginfo=2" "-Ccodegen-units=8"
stdout: none
--- stderr -------------------------------
rustc: /checkout/src/llvm-project/llvm/include/llvm/ADT/APInt.h:127: llvm::APInt::APInt(unsigned int, uint64_t, bool, bool): Assertion `llvm::isUIntN(BitWidth, val) && "Value is not an N-bit unsigned value"' failed.
------------------------------------------

---- [ui] tests/ui/autodiff/incremental.rs#DEBUG stdout end ----

failures:
---
[TIMING:end] test::Ui { test_compiler: Compiler { stage: 2, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu } -- 0.000

2 command(s) did not execute successfully:

  - env -u CARGO DOC_RUST_LANG_ORG_CHANNEL="https://doc.rust-lang.org/nightly" LD_LIBRARY_PATH="" RUSTC="/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustc" RUSTC_BOOTSTRAP="1" RUSTC_FORCE_RUSTC_VERSION="compiletest" RUST_TEST_THREADS="4" RUST_TEST_TMPDIR="/checkout/obj/build/tmp" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/compiletest" "--stage" "2" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--minicore-path" "/checkout/tests/auxiliary/minicore.rs" "--src-root" "/checkout" "--src-test-suite-root" "/checkout/tests/codegen-llvm" "--build-root" "/checkout/obj/build" "--build-test-suite-root" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm" "--sysroot-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--suite" "codegen-llvm" "--mode" "codegen" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/checkout/obj/build/x86_64-unknown-linux-gnu/llvm/build/bin/FileCheck" "--default-codegen-backend" "llvm" "--has-enzyme" "--optimize-tests" "--host-rustcflags" "-Crpath" "--host-rustcflags" "-Cdebuginfo=0" "--target-rustcflags" "-Crpath" "--target-rustcflags" "-Cdebuginfo=0" "--python" "/usr/bin/python3" "autodiff" "--verbose-run-make-subprocess-output" "--with-rustc-debug-assertions" "--with-std-debug-assertions" "--jobs" "4" "--llvm-version" "23.1.0-rust-1.99.0-nightly" "--llvm-components" "aarch64 aarch64asmparser aarch64codegen aarch64desc aarch64disassembler aarch64info aarch64utils abi aggressiveinstcombine all all-targets amdgpu amdgpuasmparser amdgpucodegen amdgpudesc amdgpudisassembler amdgpuinfo amdgputargetmca amdgpuutils analysis arm armasmparser armcodegen armdesc armdisassembler arminfo armutils asmparser asmprinter avr avrasmparser avrcodegen avrdesc avrdisassembler avrinfo binaryformat bitreader bitstreamreader bitwriter bpf bpfasmparser bpfcodegen bpfdesc bpfdisassembler bpfinfo cas cfguard cgdata codegen codegentypes core coroutines coverage csky cskyasmparser cskycodegen cskydesc cskydisassembler cskyinfo debuginfobtf debuginfocodeview debuginfodwarf debuginfodwarflowlevel debuginfogsym debuginfologicalview debuginfomsf debuginfopdb demangle dlltooldriver dtlto dwarfcfichecker dwarflinker dwarflinkerclassic dwarflinkerparallel dwp engine executionengine extensions filecheck frontendatomic frontenddirective frontenddriver frontendhlsl frontendoffloading frontendopenacc frontendopenmp fuzzercli fuzzmutate globalisel hexagon hexagonasmparser hexagoncodegen hexagondesc hexagondisassembler hexagoninfo hipstdpar instcombine instrumentation interfacestub interpreter ipo irprinter irreader jitlink libdriver lineeditor linker loongarch loongarchasmparser loongarchcodegen loongarchdesc loongarchdisassembler loongarchinfo lto m68k m68kasmparser m68kcodegen m68kdesc m68kdisassembler m68kinfo mc mca mcdisassembler mcjit mcparser mips mipsasmparser mipscodegen mipsdesc mipsdisassembler mipsinfo mirparser msp430 msp430asmparser msp430codegen msp430desc msp430disassembler msp430info native nativecodegen nvptx nvptxcodegen nvptxdesc nvptxinfo objcarcopts objcopy object objectyaml option orcdebugging orcjit orcshared orctargetprocess passes plugins powerpc powerpcasmparser powerpccodegen powerpcdesc powerpcdisassembler powerpcinfo profiledata remarks riscv riscvasmparser riscvcodegen riscvdesc riscvdisassembler riscvinfo riscvtargetmca runtimedyld sandboxir scalaropts selectiondag sparc sparcasmparser sparccodegen sparcdesc sparcdisassembler sparcinfo support supportlsp symbolize systemz systemzasmparser systemzcodegen systemzdesc systemzdisassembler systemzinfo tablegen target targetparser telemetry textapi textapibinaryreader transformutils vectorize webassembly webassemblyasmparser webassemblycodegen webassemblydesc webassemblydisassembler webassemblyinfo webassemblyutils windowsdriver windowsmanifest x86 x86asmparser x86codegen x86desc x86disassembler x86info x86targetmca xray xtensa xtensaasmparser xtensacodegen xtensadesc xtensadisassembler xtensainfo" "--cc" "" "--cxx" "" "--cflags" "" "--cxxflags" "" "--channel" "nightly" "--git-hash" "--nightly-branch" "main" "--git-merge-commit-email" "bors@rust-lang.org" (failure_mode=Exit)
  - env -u CARGO DOC_RUST_LANG_ORG_CHANNEL="https://doc.rust-lang.org/nightly" LD_LIBRARY_PATH="" RUSTC="/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustc" RUSTC_BOOTSTRAP="1" RUSTC_FORCE_RUSTC_VERSION="compiletest" RUST_TEST_THREADS="4" RUST_TEST_TMPDIR="/checkout/obj/build/tmp" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools-bin/compiletest" "--stage" "2" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--minicore-path" "/checkout/tests/auxiliary/minicore.rs" "--src-root" "/checkout" "--src-test-suite-root" "/checkout/tests/ui" "--build-root" "/checkout/obj/build" "--build-test-suite-root" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--sysroot-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--suite" "ui" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/checkout/obj/build/x86_64-unknown-linux-gnu/llvm/build/bin/FileCheck" "--default-codegen-backend" "llvm" "--has-enzyme" "--optimize-tests" "--host-rustcflags" "-Crpath" "--host-rustcflags" "-Cdebuginfo=0" "--host-rustcflags" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath" "--target-rustcflags" "-Cdebuginfo=0" "--target-rustcflags" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--python" "/usr/bin/python3" "autodiff" "feature-gates/feature-gate-autodiff.rs" "--verbose-run-make-subprocess-output" "--with-rustc-debug-assertions" "--with-std-debug-assertions" "--jobs" "4" "--llvm-version" "23.1.0-rust-1.99.0-nightly" "--llvm-components" "aarch64 aarch64asmparser aarch64codegen aarch64desc aarch64disassembler aarch64info aarch64utils abi aggressiveinstcombine all all-targets amdgpu amdgpuasmparser amdgpucodegen amdgpudesc amdgpudisassembler amdgpuinfo amdgputargetmca amdgpuutils analysis arm armasmparser armcodegen armdesc armdisassembler arminfo armutils asmparser asmprinter avr avrasmparser avrcodegen avrdesc avrdisassembler avrinfo binaryformat bitreader bitstreamreader bitwriter bpf bpfasmparser bpfcodegen bpfdesc bpfdisassembler bpfinfo cas cfguard cgdata codegen codegentypes core coroutines coverage csky cskyasmparser cskycodegen cskydesc cskydisassembler cskyinfo debuginfobtf debuginfocodeview debuginfodwarf debuginfodwarflowlevel debuginfogsym debuginfologicalview debuginfomsf debuginfopdb demangle dlltooldriver dtlto dwarfcfichecker dwarflinker dwarflinkerclassic dwarflinkerparallel dwp engine executionengine extensions filecheck frontendatomic frontenddirective frontenddriver frontendhlsl frontendoffloading frontendopenacc frontendopenmp fuzzercli fuzzmutate globalisel hexagon hexagonasmparser hexagoncodegen hexagondesc hexagondisassembler hexagoninfo hipstdpar instcombine instrumentation interfacestub interpreter ipo irprinter irreader jitlink libdriver lineeditor linker loongarch loongarchasmparser loongarchcodegen loongarchdesc loongarchdisassembler loongarchinfo lto m68k m68kasmparser m68kcodegen m68kdesc m68kdisassembler m68kinfo mc mca mcdisassembler mcjit mcparser mips mipsasmparser mipscodegen mipsdesc mipsdisassembler mipsinfo mirparser msp430 msp430asmparser msp430codegen msp430desc msp430disassembler msp430info native nativecodegen nvptx nvptxcodegen nvptxdesc nvptxinfo objcarcopts objcopy object objectyaml option orcdebugging orcjit orcshared orctargetprocess passes plugins powerpc powerpcasmparser powerpccodegen powerpcdesc powerpcdisassembler powerpcinfo profiledata remarks riscv riscvasmparser riscvcodegen riscvdesc riscvdisassembler riscvinfo riscvtargetmca runtimedyld sandboxir scalaropts selectiondag sparc sparcasmparser sparccodegen sparcdesc sparcdisassembler sparcinfo support supportlsp symbolize systemz systemzasmparser systemzcodegen systemzdesc systemzdisassembler systemzinfo tablegen target targetparser telemetry textapi textapibinaryreader transformutils vectorize webassembly webassemblyasmparser webassemblycodegen webassemblydesc webassemblydisassembler webassemblyinfo webassemblyutils windowsdriver windowsmanifest x86 x86asmparser x86codegen x86desc x86disassembler x86info x86targetmca xray xtensa xtensaasmparser xtensacodegen xtensadesc xtensadisassembler xtensainfo" "--cc" "" "--cxx" "" "--cflags" "" "--cxxflags" "" "--channel" "nightly" "--git-hash" "--nightly-branch" "main" "--git-merge-commit-email" "bors@rust-lang.org" (failure_mode=Exit)
Bootstrap failed while executing `test --stage 2 --no-fail-fast tests/codegen-llvm/autodiff tests/pretty/autodiff tests/ui/autodiff tests/ui/feature-gates/feature-gate-autodiff.rs`
Currently active steps:
Build completed unsuccessfully in 0:36:47
  local time: Wed Aug  5 12:14:49 UTC 2026
  network time: Wed, 05 Aug 2026 12:14:49 GMT

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rust-bors · 2026-08-05T14:33:52Z

☀️ Test successful - CI
Approved by: lcnr
Duration: 2h 59m 32s
Pushing 22950ab to main...

rust-log-analyzer · 2026-08-05T14:49:07Z

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rust-timer · 2026-08-05T15:15:03Z

Finished benchmarking commit (22950ab): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.3%	[0.1%, 0.6%]	12
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-3.1%, -0.1%]	13
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -0.9%, secondary 0.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	0.7%	[0.4%, 1.3%]	10
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.1%]	1
All ❌✅ (primary)	-0.9%	[-2.4%, 0.7%]	2

Cycles

Results (primary 0.1%, secondary -0.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.5%, 1.2%]	8
Regressions ❌ (secondary)	4.3%	[0.5%, 16.7%]	8
Improvements ✅ (primary)	-0.8%	[-1.1%, -0.5%]	6
Improvements ✅ (secondary)	-3.8%	[-8.2%, -0.5%]	14
All ❌✅ (primary)	0.1%	[-1.1%, 1.2%]	14

Binary size

Results (primary -0.0%, secondary -0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.0%	[-0.1%, -0.0%]	31
Improvements ✅ (secondary)	-0.0%	[-0.1%, -0.0%]	5
All ❌✅ (primary)	-0.0%	[-0.1%, -0.0%]	31

Bootstrap: 457.809s -> 454.551s (-0.71%)
Artifact size: 399.29 MiB -> 399.93 MiB (0.16%)

WaffleLapkin added 2 commits July 9, 2026 18:05

split fallback of different infer var kinds

2b4dc91

only do fallback on root vars

9dcdb29

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 9, 2026

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rust-bors Bot pushed a commit that referenced this pull request Jul 9, 2026

Auto merge of #159026 - WaffleLapkin:fallback-refactorings, r=<try>

6a25a06

Type fallback refactorings

rustbot added the T-types Relevant to the types team, which will review and decide on the PR/issue. label Jul 9, 2026

rustbot assigned oli-obk Jul 9, 2026

Urgau added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 9, 2026

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Jul 10, 2026

WaffleLapkin added 3 commits July 14, 2026 13:57

simplify never type fallback

c1686cc

tiny refactor to f32 type fallback

619c9f1

use a helper for getting unresolved root vars

8992f0e

WaffleLapkin force-pushed the fallback-refactorings branch from 68f06e3 to 8992f0e Compare July 14, 2026 12:01

rustbot added the perf-regression-triaged The performance regression has been triaged. label Jul 14, 2026

lcnr reviewed Jul 21, 2026

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Comment thread compiler/rustc_hir_typeck/src/fallback.rs Outdated

Comment thread compiler/rustc_infer/src/infer/type_variable.rs Outdated

lcnr reviewed Jul 21, 2026

View reviewed changes

Comment thread compiler/rustc_hir_typeck/src/fallback.rs Outdated

oli-obk assigned lcnr and unassigned oli-obk Jul 21, 2026

WaffleLapkin and others added 3 commits July 22, 2026 13:47

mention FCW lint in a comment

9e7646c

don't needlessly use OnceCell

1ed1260

Bump ena

997bde3

rustbot removed the perf-regression Performance regression. label Jul 29, 2026

use new functions from the ena bump

4ac3cec

WaffleLapkin force-pushed the fallback-refactorings branch from 680fc04 to 4ac3cec Compare July 30, 2026 13:11

rust-bors Bot 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 5, 2026

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rust-bors Bot 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 Aug 5, 2026

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JonathanBrouwer mentioned this pull request Aug 5, 2026

Update to LLVM 23 #158734

Merged

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rust-bors Bot added merged-by-bors This PR was explicitly merged by bors. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 5, 2026

rust-bors Bot merged commit 22950ab into rust-lang:main Aug 5, 2026
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rustbot added this to the 1.99.0 milestone Aug 5, 2026

This was referenced Aug 5, 2026

Implement "low priority impls" #159003

Draft

trait_selection: fix assumptions-on-binders diagnostics #158588

Open

rustbot added the perf-regression Performance regression. label Aug 5, 2026

WaffleLapkin deleted the fallback-refactorings branch August 6, 2026 09:13

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Overall result: ❌✅ regressions and improvements - please read:

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Overall result: ❌✅ regressions and improvements - please read:

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WaffleLapkin commented Jul 9, 2026 •

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