Skip redundant monomorphization checks by charliermarsh · Pull Request #164330 · rust-lang/rust

charliermarsh · 2026-10-14T21:38:16Z

Summary

This PR attempts to avoid unnecessary work during call-site ABI checks. On main, we instantiate generic arguments and normalize the callee type, but then immediately return for Rust ABIs and LLVM intrinsics.

Since the ABI doesn't depend on generic arguments, we can instead check it first and skip that preparation if the subsequent checks would be a no-op.

rustbot · 2026-10-14T21:38:23Z

r? @adwinwhite

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Kobzol · 2026-10-14T22:13:43Z

@bors try @rust-timer queue

…ks, r=<try> Skip redundant monomorphization checks

rust-bors · 2026-10-14T23:13:31Z

☀️ Try build successful (CI)
Build commit: dea04eb (dea04eb7af15ea77b8bdb45a3a68294aa5361af4)
Base parent: 7df8138 (7df81381d027710708209f36b98d11b1c88f8d2e)

rust-timer · 2026-10-15T01:18:20Z

Finished benchmarking commit (dea04eb): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@bors rollup=iffy rustc-perf
@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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-0.8%, -0.2%]	2
Improvements ✅ (secondary)	-0.3%	[-0.6%, -0.2%]	6
All ❌✅ (primary)	-0.5%	[-0.8%, -0.2%]	2

Max RSS (memory usage)

This perf run didn't have relevant results for this metric.

Cycles

Results (secondary 1.0%)

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)	5.1%	[5.1%, 5.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-3.0%, -3.0%]	1
All ❌✅ (primary)	-	-	0

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 489.902s -> 489.636s (-0.05%)
Artifact size: 407.05 MiB -> 407.13 MiB (0.02%)

ShoyuVanilla · 2026-10-15T15:20:29Z

CI failure is sus. Re-triggering it.

adwinwhite · 2026-10-19T02:04:54Z

Given that this fast path has a soundness hole (see check_call_site_abi), I don't think we should duplicate it outside.
Perhaps we can move the instantiate_mir_and_normalize_erasing_regions into check_call_site_abi and skip in check_call_site_abi?

adwinwhite

nits :>

View changes since this review

adwinwhite · 2026-10-20T01:44:05Z

+    instance: Instance<'tcx>,
    caller: InstanceKind<'tcx>,


Could we replace caller: InstanceKind with caller: Instance and avoid the redundant arguments?

adwinwhite · 2026-10-20T01:49:34Z

-    let extern_abi = callee.fn_sig(tcx).abi();
+    // The ABI does not depend on generic arguments.
+    let extern_abi = match *callee.kind() {
+        ty::FnDef(def_id, _) => tcx.fn_sig(def_id).skip_binder().abi(),
+        _ => callee.fn_sig(tcx).abi(),
+    };


We can call .fn_sig(tcx).abi() as before?

adwinwhite · 2026-10-21T12:03:38Z

@bors r+ rollup

rust-bors · 2026-10-21T12:03:41Z

📌 Commit a498a55 has been approved by adwinwhite

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 5. This pull request will be tested once the tree is reopened.

Reason for tree closure: spurious failures

…nt-abi-checks, r=adwinwhite Skip redundant monomorphization checks ## Summary This PR attempts to avoid unnecessary work during call-site ABI checks. On main, we instantiate generic arguments and normalize the callee type, but then immediately return for Rust ABIs and LLVM intrinsics. Since the ABI doesn't depend on generic arguments, we can instead check it first and skip that preparation if the subsequent checks would be a no-op.

…uwer Rollup of 8 pull requests Successful merges: - #162460 (Feat - `#[inline(always)] + #[target_feature(enable = "....")]` #2) - #163485 (`rustc_builtin_macros` cleanup, part 8) - #164578 (Don't ignore unknown LLVM diagnostics) - #162369 (Document the `recursion_limit` built-in attribute) - #162840 (tier 3 target policy: target CPU and features must be supported by upstream backend) - #164330 (Skip redundant monomorphization checks) - #164656 (stabilize ExitCodeExt for Windows) - #164660 (Touch up attribute docs)

…nt-abi-checks, r=adwinwhite Skip redundant monomorphization checks ## Summary This PR attempts to avoid unnecessary work during call-site ABI checks. On main, we instantiate generic arguments and normalize the callee type, but then immediately return for Rust ABIs and LLVM intrinsics. Since the ABI doesn't depend on generic arguments, we can instead check it first and skip that preparation if the subsequent checks would be a no-op.

…uwer Rollup of 13 pull requests Successful merges: - #162460 (Feat - `#[inline(always)] + #[target_feature(enable = "....")]` #2) - #163485 (`rustc_builtin_macros` cleanup, part 8) - #164457 (Add `vec_visualizer` lldb test) - #161253 (Implement `AsMut<T>` and `AsRef<T>` for `!`.) - #162369 (Document the `recursion_limit` built-in attribute) - #162840 (tier 3 target policy: target CPU and features must be supported by upstream backend) - #164329 (use default_field_values in declare_lint) - #164330 (Skip redundant monomorphization checks) - #164527 (doc: added addtional docs for Write) - #164656 (stabilize ExitCodeExt for Windows) - #164660 (Touch up attribute docs) - #164681 (tidy: use repository-relative path for style checks) - #164688 (re-enable test_dir_remove_dir test on QNX)

Rollup merge of #164330 - charliermarsh:charlie/skip-redundant-abi-checks, r=adwinwhite Skip redundant monomorphization checks ## Summary This PR attempts to avoid unnecessary work during call-site ABI checks. On main, we instantiate generic arguments and normalize the callee type, but then immediately return for Rust ABIs and LLVM intrinsics. Since the ABI doesn't depend on generic arguments, we can instead check it first and skip that preparation if the subsequent checks would be a no-op.

Skip redundant monomorphization checks

2e17971

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 14, 2026

rustbot assigned adwinwhite Oct 14, 2026

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 14, 2026

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rust-bors Bot pushed a commit that referenced this pull request Oct 14, 2026

Auto merge of #164330 - charliermarsh:charlie/skip-redundant-abi-chec…

dea04eb

…ks, r=<try> Skip redundant monomorphization checks

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 15, 2026

Keep call-site ABI normalization inside the check

8aae035

adwinwhite reviewed Oct 20, 2026

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Simplify call-site ABI checks

a498a55

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 Oct 21, 2026

JonathanBrouwer mentioned this pull request Oct 21, 2026

Rollup of 8 pull requests #164687

Closed

This was referenced Oct 21, 2026

Rollup of 14 pull requests #164697

Closed

Rollup of 13 pull requests #164699

Merged

rust-bors Bot merged commit 7658469 into rust-lang:main Oct 21, 2026
14 checks passed

rustbot added this to the 1.101.0 milestone Oct 21, 2026

github-actions Bot mentioned this pull request Oct 22, 2026

Toolchain upgrade to nightly-2026-10-22 flux-rs/flux#1847

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charliermarsh commented Oct 14, 2026

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rust-timer commented Oct 15, 2026

Overall result: ✅ improvements - no action needed

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ShoyuVanilla commented Oct 15, 2026

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adwinwhite commented Oct 19, 2026

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