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fix: handle zero-sized memory intrinsics #876

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fix: handle zero-sized memory intrinsics #876

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88c3abf
fix: handle zero-sized memory intrinsics
mizoz Apr 28, 2026
3a2a9f0
fix: skip zero-sized memory builtins in builder
mizoz Apr 29, 2026
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2 changes: 2 additions & 0 deletions example/mini_core.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -662,6 +662,8 @@ pub mod intrinsics {
#[rustc_intrinsic]
pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize);
#[rustc_intrinsic]
pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
#[rustc_intrinsic]
pub unsafe fn transmute<T, U>(e: T) -> U;
#[rustc_intrinsic]
pub unsafe fn ctlz_nonzero<T>(x: T) -> u32;
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7 changes: 7 additions & 0 deletions src/intrinsic/mod.rs
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Expand Up @@ -338,6 +338,13 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tc
);
return Ok(());
}
sym::copy | sym::copy_nonoverlapping | sym::write_bytes => {
let ty = fn_args.type_at(0);
if self.layout_of(ty).size.bytes() == 0 {
return Ok(());
}
return Err(Instance::new_raw(instance.def_id(), instance.args));
}
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@bjorn3 bjorn3 Apr 28, 2026 •
edited by rustbot
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Why not change the memset, memcpy and memmove methods on Builder? Also this only helps with ZST types, not with copying zero elements.

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sym::breakpoint => {
unimplemented!();
}
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28 changes: 28 additions & 0 deletions tests/run/zero_sized_mem.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
// Compiler:
//
// Run-time:
// status: 0

#![feature(no_core)]
#![no_std]
#![no_core]
#![no_main]

extern crate mini_core;
use mini_core::*;

#[inline(never)]
unsafe fn zero_sized_mem_ops(count: usize) {
let src = 0usize as *const ();
let dst = 0usize as *mut ();

intrinsics::copy_nonoverlapping(src, dst, count);
intrinsics::copy(src, dst, count);
intrinsics::write_bytes(dst, 0xab, count);
}

#[no_mangle]
extern "C" fn main(_argc: i32, _argv: *const *const u8) -> i32 {
unsafe { zero_sized_mem_ops(1) };
0
}
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