Don't compute FnAbi for LLVM intrinsics in backends by bjorn3 · Pull Request #150768 · rust-lang/rust

bjorn3 · 2026-01-07T15:08:29Z

This removes support for extern "unadjusted" for anything other than LLVM intrinsics. It only makes sense in the context of calling LLVM intrinsics anyway as it exposes the way the LLVM backend internally represents types. Perhaps it should be renamed to extern "llvm-intrinsic"?

Follow up to #148533

bjorn3 · 2026-01-07T15:10:29Z

cc @sayantn this would make #140763 a tiny bit simpler I think. You don't have to modify compiler/rustc_codegen_llvm/src/abi.rs anymore.

rustbot · 2026-01-07T16:11:39Z

These commits modify compiler targets.
(See the Target Tier Policy.)

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

rustbot · 2026-01-07T16:11:43Z

r? @wesleywiser

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rustbot · 2026-01-08T10:47:46Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

bjorn3 · 2026-01-08T10:48:53Z

I've removed the removal of computing an FnAbi for extern "unadjusted" as miri still depends on it. Will remove it in a follow up PR.

sayantn

Thanks a lot @bjorn3 ❤️

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compiler/rustc_codegen_llvm/src/intrinsic.rs

bjorn3 · 2026-02-08T19:47:45Z

@wesleywiser are you able to review this or should I reroll for review?

Mark-Simulacrum · 2026-02-08T20:04:48Z

compiler/rustc_codegen_llvm/src/intrinsic.rs

                    self,
                    sym,
-                    fn_abi.llvm_cconv(self),
+                    llvm::CCallConv,


Is this effectively just a lie? Or how does LLVM model the ABI for intrinsics? Is there a hidden assumption here that intrinsics only ever take ~integers/pointers that don't have any special handling in terms of ABI lowering of the arguments?

This matches what was effectively done previously. I don't know if LLVM actually cares about the calling convention for intrinsics. It recognizes intrinsics based on a builtin list of symbol names. (if you declare an llvm.* function that doesn't match a known intrinsic, it will treat it like a regular function and emit an import of said function in the emitted object file)

Mark-Simulacrum · 2026-02-08T20:06:16Z

compiler/rustc_codegen_gcc/src/intrinsic/mod.rs

-                for fn_attr in fn_ty.fn_attributes {
-                    func.add_attribute(fn_attr);
-                }
+                self.on_stack_function_params.borrow_mut().insert(func, FxHashSet::default());


I guess this is the same ABI question as below - we're assuming there's no on-stack parameter passing since it's an intrinsic?

extern "unadjusted" previously forced PassMode::Direct for all arguments, which means that on-stack parameters would never occur.

wesleywiser

One question but feel free to r=me

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compiler/rustc_codegen_gcc/src/intrinsic/mod.rs

bjorn3 · 2026-02-11T08:18:17Z

@bors r=wesleywiser

rust-bors · 2026-02-11T08:18:19Z

📌 Commit fe9715b has been approved by wesleywiser

It is now in the queue for this repository.

…=wesleywiser Don't compute FnAbi for LLVM intrinsics in backends ~~This removes support for `extern "unadjusted"` for anything other than LLVM intrinsics. It only makes sense in the context of calling LLVM intrinsics anyway as it exposes the way the LLVM backend internally represents types. Perhaps it should be renamed to `extern "llvm-intrinsic"`?~~ Follow up to rust-lang#148533

Rollup of 17 pull requests Successful merges: - #142415 (Add note when inherent impl for a alias type defined outside of the crate) - #142680 (Fix passing/returning structs with the 64-bit SPARC ABI) - #150768 (Don't compute FnAbi for LLVM intrinsics in backends) - #151152 (Add FCW for derive helper attributes that will conflict with built-in attributes) - #151814 (layout: handle rigid aliases without params) - #151863 (Borrowck: simplify diagnostics for placeholders) - #152159 (Add note for `?Sized` params in int-ptr casts diag) - #152434 (Clarify names of `QueryVTable` functions for "executing" a query) - #152478 (Remove tm_factory field from CodegenContext) - #152498 (Partially revert "resolve: Update `NameBindingData::vis` in place") - #152316 (fix: add continue) - #152394 (Correctly check if a macro call is actually a macro call in rustdoc highlighter) - #152425 (Port #![test_runner] to the attribute parser) - #152481 (Use cg_ssa's produce_final_output_artifacts in cg_clif) - #152485 (fix issue#152482) - #152495 (Clean up some subdiagnostics) - #152502 (Implement `BinaryHeap::from_raw_vec`)

Rollup merge of #150768 - bjorn3:llvm_intrinsic_no_fn_abi, r=wesleywiser Don't compute FnAbi for LLVM intrinsics in backends ~~This removes support for `extern "unadjusted"` for anything other than LLVM intrinsics. It only makes sense in the context of calling LLVM intrinsics anyway as it exposes the way the LLVM backend internally represents types. Perhaps it should be renamed to `extern "llvm-intrinsic"`?~~ Follow up to #148533

bjorn3 marked this pull request as ready for review January 7, 2026 16:11

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bjorn3 force-pushed the llvm_intrinsic_no_fn_abi branch 2 times, most recently from fb63e0c to af005a9 Compare January 7, 2026 16:30

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bjorn3 force-pushed the llvm_intrinsic_no_fn_abi branch from b05795a to 83e77ec Compare January 7, 2026 18:44

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bjorn3 added 2 commits January 8, 2026 10:45

Reduce usage of FnAbi in codegen_llvm_intrinsic_call

acc8c0b

Don't compute FnAbi for LLVM intrinsics in backends

f1ab003

bjorn3 force-pushed the llvm_intrinsic_no_fn_abi branch from 83e77ec to f1ab003 Compare January 8, 2026 10:47

bjorn3 changed the title ~~Don't compute FnAbi for LLVM intrinsics~~ Don't compute FnAbi for LLVM intrinsics in backends Jan 8, 2026

sayantn reviewed Jan 8, 2026

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Remove support for ScalarPair unadjusted arguments

fe9715b

Mark-Simulacrum reviewed Feb 8, 2026

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wesleywiser approved these changes Feb 10, 2026

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Zalathar mentioned this pull request Feb 11, 2026

[EXPERIMENT] Rollup of 9 pull requests #152476

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[EXPERIMENT] Rollup of 8 pull requests #152479

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[EXPERIMENT] Rollup of 18 pull requests #152513

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jhpratt mentioned this pull request Feb 12, 2026

Rollup of 17 pull requests #152517

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rust-bors bot merged commit 0041f22 into rust-lang:main Feb 12, 2026
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rustbot added this to the 1.95.0 milestone Feb 12, 2026

bjorn3 deleted the llvm_intrinsic_no_fn_abi branch February 12, 2026 10:40

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