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enable PassMode::Indirect { on_stack: true, .. } tail call arguments #153361

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Merged
rust-bors merged 1 commit into from
Mar 5, 2026
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enable PassMode::Indirect { on_stack: true, .. } tail call arguments #153361

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74 changes: 28 additions & 46 deletions compiler/rustc_codegen_ssa/src/mir/block.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1256,55 +1256,37 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
}
CallKind::Tail => {
match fn_abi.args[i].mode {
PassMode::Indirect { on_stack: false, .. } => {
let Some(tmp) = tail_call_temporaries[i].take() else {
span_bug!(
fn_span,
"missing temporary for indirect tail call argument #{i}"
)
};

let local = self.mir.args_iter().nth(i).unwrap();

match &self.locals[local] {
LocalRef::Place(arg) => {
bx.typed_place_copy(arg.val, tmp.val, fn_abi.args[i].layout);
op.val = Ref(arg.val);
}
LocalRef::Operand(arg) => {
let Ref(place_value) = arg.val else {
bug!("only `Ref` should use `PassMode::Indirect`");
};
bx.typed_place_copy(
place_value,
tmp.val,
fn_abi.args[i].layout,
);
op.val = arg.val;
}
LocalRef::UnsizedPlace(_) => {
span_bug!(fn_span, "unsized types are not supported")
}
LocalRef::PendingOperand => {
span_bug!(fn_span, "argument local should not be pending")
}
};

bx.lifetime_end(tmp.val.llval, tmp.layout.size);
}
PassMode::Indirect { on_stack: true, .. } => {
// FIXME: some LLVM backends (notably x86) do not correctly pass byval
// arguments to tail calls (as of LLVM 21). See also:
//
// - https://github.com/rust-lang/rust/pull/144232#discussion_r2218543841
// - https://github.com/rust-lang/rust/issues/144855
Comment on lines -1297 to -1301
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@WaffleLapkin WaffleLapkin Mar 4, 2026

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Is this comment not accurate anymore, shouldn't we wait until we don't support llvm 21 anymore?

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@folkertdev folkertdev Mar 4, 2026

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you can only use tail calls with nightly, which builds with the latest LLVM? We'll need to wait until we don't support LLVM 21 (or higher, given that e.g. riscv will only add support in LLVM 23) for stabilization, but not for experimentation.

if let PassMode::Indirect { on_stack: false, .. } = fn_abi.args[i].mode {
let Some(tmp) = tail_call_temporaries[i].take() else {
span_bug!(
fn_span,
"arguments using PassMode::Indirect {{ on_stack: true, .. }} are currently not supported for tail calls"
"missing temporary for indirect tail call argument #{i}"
)
}
_ => (),
};

let local = self.mir.args_iter().nth(i).unwrap();

match &self.locals[local] {
LocalRef::Place(arg) => {
bx.typed_place_copy(arg.val, tmp.val, fn_abi.args[i].layout);
op.val = Ref(arg.val);
}
LocalRef::Operand(arg) => {
let Ref(place_value) = arg.val else {
bug!("only `Ref` should use `PassMode::Indirect`");
};
bx.typed_place_copy(place_value, tmp.val, fn_abi.args[i].layout);
op.val = arg.val;
}
LocalRef::UnsizedPlace(_) => {
span_bug!(fn_span, "unsized types are not supported")
}
LocalRef::PendingOperand => {
span_bug!(fn_span, "argument local should not be pending")
}
};

bx.lifetime_end(tmp.val.llval, tmp.layout.size);
}
}
}
Expand Down
97 changes: 97 additions & 0 deletions tests/ui/explicit-tail-calls/support/basic.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,97 @@
//@ build-pass
//@ ignore-backends: gcc
//@ add-minicore
//@ min-llvm-version: 22
//
//@ revisions: i686
//@[i686] compile-flags: --target i686-unknown-linux-gnu
//@[i686] needs-llvm-components: x86
//@ revisions: x86-64
//@[x86-64] compile-flags: --target x86_64-unknown-linux-gnu
//@[x86-64] needs-llvm-components: x86
//@ revisions: x86-64-win
//@[x86-64-win] compile-flags: --target x86_64-pc-windows-msvc
//@[x86-64-win] needs-llvm-components: x86
//@ revisions: arm
//@[arm] compile-flags: --target arm-unknown-linux-gnueabi
//@[arm] needs-llvm-components: arm
//@ revisions: thumb
//@[thumb] compile-flags: --target thumbv8m.main-none-eabi
//@[thumb] needs-llvm-components: arm
//@ revisions: aarch64
//@[aarch64] compile-flags: --target aarch64-unknown-linux-gnu
//@[aarch64] needs-llvm-components: aarch64
//@ revisions: s390x
//@[s390x] compile-flags: --target s390x-unknown-linux-gnu
//@[s390x] needs-llvm-components: systemz
//@ revisions: sparc
//@[sparc] compile-flags: --target sparc-unknown-linux-gnu
//@[sparc] needs-llvm-components: sparc
//@ revisions: sparc64
//@[sparc64] compile-flags: --target sparc64-unknown-linux-gnu
//@[sparc64] needs-llvm-components: sparc
//@ revisions: powerpc64
//@[powerpc64] compile-flags: --target powerpc64-unknown-linux-gnu
//@[powerpc64] needs-llvm-components: powerpc
//@ revisions: riscv
//@[riscv] compile-flags: --target riscv64gc-unknown-linux-gnu
//@[riscv] needs-llvm-components: riscv
//@ revisions: loongarch32
//@[loongarch32] compile-flags: --target loongarch32-unknown-none
//@[loongarch32] needs-llvm-components: loongarch
//@ revisions: loongarch64
//@[loongarch64] compile-flags: --target loongarch64-unknown-linux-gnu
//@[loongarch64] needs-llvm-components: loongarch
//@ revisions: bpf
//@[bpf] compile-flags: --target bpfeb-unknown-none
//@[bpf] needs-llvm-components: bpf
//@ revisions: m68k
//@[m68k] compile-flags: --target m68k-unknown-linux-gnu
//@[m68k] needs-llvm-components: m68k
//@ revisions: nvptx64
//@[nvptx64] compile-flags: --target nvptx64-nvidia-cuda
//@[nvptx64] needs-llvm-components: nvptx
//
// Wasm needs a special target feature.
//
//@ revisions: wasm
//@[wasm] compile-flags: --target wasm32-unknown-unknown -Ctarget-feature=+tail-call
//@[wasm] needs-llvm-components: webassembly
//@ revisions: wasip1
//@[wasip1] compile-flags: --target wasm32-wasip1 -Ctarget-feature=+tail-call
//@[wasip1] needs-llvm-components: webassembly
//
// Failing cases (just zero support)
//
// //@ revisions: powerpc
// //@[powerpc] compile-flags: --target powerpc-unknown-linux-gnu
// //@[powerpc] needs-llvm-components: powerpc
// //@ revisions: aix
// //@[aix] compile-flags: --target powerpc64-ibm-aix
// //@[aix] needs-llvm-components: powerpc
// //@ revisions: csky
// //@[csky] compile-flags: --target csky-unknown-linux-gnuabiv2
// //@[csky] needs-llvm-components: csky
// //@ revisions: mips
// //@[mips] compile-flags: --target mips-unknown-linux-gnu
// //@[mips] needs-llvm-components: mips
// //@ revisions: mips64
// //@[mips64] compile-flags: --target mips64-unknown-linux-gnuabi64
// //@[mips64] needs-llvm-components: mips
#![feature(no_core, explicit_tail_calls)]
#![expect(incomplete_features)]
#![no_core]
#![crate_type = "lib"]

extern crate minicore;
use minicore::*;

#[inline(never)]
fn simple1(x: u64) -> u64 {
x
}

#[unsafe(no_mangle)]
fn simple2(x: u64) -> u64 {
become simple1(x);
}
108 changes: 108 additions & 0 deletions tests/ui/explicit-tail-calls/support/bystack.rs
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@@ -0,0 +1,108 @@
//@ build-pass
//@ ignore-backends: gcc
//@ add-minicore
//@ min-llvm-version: 22
//
//@ revisions: i686
//@[i686] compile-flags: --target i686-unknown-linux-gnu
//@[i686] needs-llvm-components: x86
//@ revisions: x86-64
//@[x86-64] compile-flags: --target x86_64-unknown-linux-gnu
//@[x86-64] needs-llvm-components: x86
//@ revisions: x86-64-win
//@[x86-64-win] compile-flags: --target x86_64-pc-windows-msvc
//@[x86-64-win] needs-llvm-components: x86
//@ revisions: arm
//@[arm] compile-flags: --target arm-unknown-linux-gnueabi
//@[arm] needs-llvm-components: arm
//@ revisions: thumb
//@[thumb] compile-flags: --target thumbv8m.main-none-eabi
//@[thumb] needs-llvm-components: arm
//@ revisions: aarch64
//@[aarch64] compile-flags: --target aarch64-unknown-linux-gnu
//@[aarch64] needs-llvm-components: aarch64
//@ revisions: s390x
//@[s390x] compile-flags: --target s390x-unknown-linux-gnu
//@[s390x] needs-llvm-components: systemz
//@ revisions: sparc
//@[sparc] compile-flags: --target sparc-unknown-linux-gnu
//@[sparc] needs-llvm-components: sparc
//@ revisions: sparc64
//@[sparc64] compile-flags: --target sparc64-unknown-linux-gnu
//@[sparc64] needs-llvm-components: sparc
//@ revisions: powerpc64
//@[powerpc64] compile-flags: --target powerpc64-unknown-linux-gnu
//@[powerpc64] needs-llvm-components: powerpc
//@ revisions: loongarch32
//@[loongarch32] compile-flags: --target loongarch32-unknown-none
//@[loongarch32] needs-llvm-components: loongarch
//@ revisions: loongarch64
//@[loongarch64] compile-flags: --target loongarch64-unknown-linux-gnu
//@[loongarch64] needs-llvm-components: loongarch
//@ revisions: bpf
//@[bpf] compile-flags: --target bpfeb-unknown-none
//@[bpf] needs-llvm-components: bpf
//@ revisions: m68k
//@[m68k] compile-flags: --target m68k-unknown-linux-gnu
//@[m68k] needs-llvm-components: m68k
//@ revisions: nvptx64
//@[nvptx64] compile-flags: --target nvptx64-nvidia-cuda
//@[nvptx64] needs-llvm-components: nvptx
//
// Riscv does not support byval in LLVM 22 (but wil in LLVM 23)
//
// //@ revisions: riscv
// //@[riscv] compile-flags: --target riscv64gc-unknown-linux-gnu
// //@[riscv] needs-llvm-components: riscv
//
// Wasm needs a special target feature.
//
//@ revisions: wasm
//@[wasm] compile-flags: --target wasm32-unknown-unknown -Ctarget-feature=+tail-call
//@[wasm] needs-llvm-components: webassembly
//@ revisions: wasip1
//@[wasip1] compile-flags: --target wasm32-wasip1 -Ctarget-feature=+tail-call
//@[wasip1] needs-llvm-components: webassembly
//
// Failing cases (just zero support)
//
// //@ revisions: powerpc
// //@[powerpc] compile-flags: --target powerpc-unknown-linux-gnu
// //@[powerpc] needs-llvm-components: powerpc
// //@ revisions: aix
// //@[aix] compile-flags: --target powerpc64-ibm-aix
// //@[aix] needs-llvm-components: powerpc
// //@ revisions: csky
// //@[csky] compile-flags: --target csky-unknown-linux-gnuabiv2
// //@[csky] needs-llvm-components: csky
// //@ revisions: mips
// //@[mips] compile-flags: --target mips-unknown-linux-gnu
// //@[mips] needs-llvm-components: mips
// //@ revisions: mips64
// //@[mips64] compile-flags: --target mips64-unknown-linux-gnuabi64
// //@[mips64] needs-llvm-components: mips
#![feature(no_core, explicit_tail_calls)]
#![expect(incomplete_features)]
#![no_core]
#![crate_type = "lib"]

extern crate minicore;
use minicore::*;

#[repr(C)]
struct PassedByVal {
a: u64,
b: u64,
c: u64,
d: u64,
}

#[inline(never)]
extern "C" fn callee(x: PassedByVal) -> PassedByVal {
x
}

#[unsafe(no_mangle)]
extern "C" fn byval(x: PassedByVal) -> PassedByVal {
become callee(x);
}
108 changes: 108 additions & 0 deletions tests/ui/explicit-tail-calls/support/byval.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,108 @@
//@ build-pass
//@ ignore-backends: gcc
//@ add-minicore
//@ min-llvm-version: 22
//
//@ revisions: i686
//@[i686] compile-flags: --target i686-unknown-linux-gnu
//@[i686] needs-llvm-components: x86
//@ revisions: x86-64
//@[x86-64] compile-flags: --target x86_64-unknown-linux-gnu
//@[x86-64] needs-llvm-components: x86
//@ revisions: x86-64-win
//@[x86-64-win] compile-flags: --target x86_64-pc-windows-msvc
//@[x86-64-win] needs-llvm-components: x86
//@ revisions: arm
//@[arm] compile-flags: --target arm-unknown-linux-gnueabi
//@[arm] needs-llvm-components: arm
//@ revisions: thumb
//@[thumb] compile-flags: --target thumbv8m.main-none-eabi
//@[thumb] needs-llvm-components: arm
//@ revisions: aarch64
//@[aarch64] compile-flags: --target aarch64-unknown-linux-gnu
//@[aarch64] needs-llvm-components: aarch64
//@ revisions: s390x
//@[s390x] compile-flags: --target s390x-unknown-linux-gnu
//@[s390x] needs-llvm-components: systemz
//@ revisions: sparc
//@[sparc] compile-flags: --target sparc-unknown-linux-gnu
//@[sparc] needs-llvm-components: sparc
//@ revisions: sparc64
//@[sparc64] compile-flags: --target sparc64-unknown-linux-gnu
//@[sparc64] needs-llvm-components: sparc
//@ revisions: powerpc64
//@[powerpc64] compile-flags: --target powerpc64-unknown-linux-gnu
//@[powerpc64] needs-llvm-components: powerpc
//@ revisions: loongarch32
//@[loongarch32] compile-flags: --target loongarch32-unknown-none
//@[loongarch32] needs-llvm-components: loongarch
//@ revisions: loongarch64
//@[loongarch64] compile-flags: --target loongarch64-unknown-linux-gnu
//@[loongarch64] needs-llvm-components: loongarch
//@ revisions: bpf
//@[bpf] compile-flags: --target bpfeb-unknown-none
//@[bpf] needs-llvm-components: bpf
//@ revisions: m68k
//@[m68k] compile-flags: --target m68k-unknown-linux-gnu
//@[m68k] needs-llvm-components: m68k
//@ revisions: nvptx64
//@[nvptx64] compile-flags: --target nvptx64-nvidia-cuda
//@[nvptx64] needs-llvm-components: nvptx
//
// Riscv does not support byval in LLVM 22 (but wil in LLVM 23)
//
// //@ revisions: riscv
// //@[riscv] compile-flags: --target riscv64gc-unknown-linux-gnu
// //@[riscv] needs-llvm-components: riscv
//
// Wasm needs a special target feature.
//
//@ revisions: wasm
//@[wasm] compile-flags: --target wasm32-unknown-unknown -Ctarget-feature=+tail-call
//@[wasm] needs-llvm-components: webassembly
//@ revisions: wasip1
//@[wasip1] compile-flags: --target wasm32-wasip1 -Ctarget-feature=+tail-call
//@[wasip1] needs-llvm-components: webassembly
//
// Failing cases (just zero support)
//
// //@ revisions: powerpc
// //@[powerpc] compile-flags: --target powerpc-unknown-linux-gnu
// //@[powerpc] needs-llvm-components: powerpc
// //@ revisions: aix
// //@[aix] compile-flags: --target powerpc64-ibm-aix
// //@[aix] needs-llvm-components: powerpc
// //@ revisions: csky
// //@[csky] compile-flags: --target csky-unknown-linux-gnuabiv2
// //@[csky] needs-llvm-components: csky
// //@ revisions: mips
// //@[mips] compile-flags: --target mips-unknown-linux-gnu
// //@[mips] needs-llvm-components: mips
// //@ revisions: mips64
// //@[mips64] compile-flags: --target mips64-unknown-linux-gnuabi64
// //@[mips64] needs-llvm-components: mips
#![feature(no_core, explicit_tail_calls)]
#![expect(incomplete_features)]
#![no_core]
#![crate_type = "lib"]

extern crate minicore;
use minicore::*;

// The rust calling convention will pass this by-value.
struct PassedByVal {
a: u64,
b: u64,
c: u64,
d: u64,
}

#[inline(never)]
fn callee(x: PassedByVal) -> PassedByVal {
x
}

#[unsafe(no_mangle)]
fn byval(x: PassedByVal) -> PassedByVal {
become callee(x);
}
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