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Skip parameter attribute deduction for MIR with spread_arg #148131

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Merged
merged 1 commit into from
Oct 29, 2025
Merged

Skip parameter attribute deduction for MIR with spread_arg #148131

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5 changes: 5 additions & 0 deletions compiler/rustc_mir_transform/src/deduce_param_attrs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -195,6 +195,11 @@ pub(super) fn deduced_param_attrs<'tcx>(

// Grab the optimized MIR. Analyze it to determine which arguments have been mutated.
let body: &Body<'tcx> = tcx.optimized_mir(def_id);
// Arguments spread at ABI level are currently unsupported.
if body.spread_arg.is_some() {
return &[];
}

let mut deduce = DeduceParamAttrs::new(body);
deduce.visit_body(body);
tracing::trace!(?deduce.usage);
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10 changes: 9 additions & 1 deletion tests/codegen-llvm/deduced-param-attrs.rs
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Expand Up @@ -3,7 +3,7 @@
//@ revisions: LLVM21 LLVM20
//@ [LLVM21] min-llvm-version: 21
//@ [LLVM20] max-llvm-major-version: 20
#![feature(custom_mir, core_intrinsics)]
#![feature(custom_mir, core_intrinsics, unboxed_closures)]
#![crate_type = "lib"]
extern crate core;
use core::intrinsics::mir::*;
Expand Down Expand Up @@ -170,3 +170,11 @@ pub fn not_captured_return_place() -> [u8; 80] {
pub fn captured_return_place() -> [u8; 80] {
black_box([0u8; 80])
}

// Arguments spread at ABI level are unsupported.
//
// CHECK-LABEL: @spread_arg(
// CHECK-NOT: readonly
// CHECK-SAME: )
#[no_mangle]
pub extern "rust-call" fn spread_arg(_: (Big, Big, Big)) {}
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