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Auto merge of #142911 - mejrs:unsized, r=compiler-errors

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Remove support for dynamic allocas

Followup to rust-lang/rust#141811
This commit is contained in:
bors
2025-07-11 05:27:32 +00:00
parent cdac44e608 25eb3829e5
commit 855e0fe46e
16 changed files with 163 additions and 94 deletions
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40
compiler/rustc_codegen_ssa/src/mir/operand.rs
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@@ -16,9 +16,9 @@ use tracing::{debug, instrument};
use super::place::{PlaceRef, PlaceValue};
use super::rvalue::transmute_scalar;
use super::{FunctionCx, LocalRef};
use crate::MemFlags;
use crate::common::IntPredicate;
use crate::traits::*;
use crate::{MemFlags, size_of_val};
/// The representation of a Rust value. The enum variant is in fact
/// uniquely determined by the value's type, but is kept as a
@@ -861,44 +861,6 @@ impl<'a, 'tcx, V: CodegenObject> OperandValue<V> {
}
}
}
pub fn store_unsized<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
self,
bx: &mut Bx,
indirect_dest: PlaceRef<'tcx, V>,
) {
debug!("OperandRef::store_unsized: operand={:?}, indirect_dest={:?}", self, indirect_dest);
// `indirect_dest` must have `*mut T` type. We extract `T` out of it.
let unsized_ty = indirect_dest
.layout
.ty
.builtin_deref(true)
.unwrap_or_else(|| bug!("indirect_dest has non-pointer type: {:?}", indirect_dest));
let OperandValue::Ref(PlaceValue { llval: llptr, llextra: Some(llextra), .. }) = self
else {
bug!("store_unsized called with a sized value (or with an extern type)")
};
// Allocate an appropriate region on the stack, and copy the value into it. Since alloca
// doesn't support dynamic alignment, we allocate an extra align - 1 bytes, and align the
// pointer manually.
let (size, align) = size_of_val::size_and_align_of_dst(bx, unsized_ty, Some(llextra));
let one = bx.const_usize(1);
let align_minus_1 = bx.sub(align, one);
let size_extra = bx.add(size, align_minus_1);
let min_align = Align::ONE;
let alloca = bx.dynamic_alloca(size_extra, min_align);
let address = bx.ptrtoint(alloca, bx.type_isize());
let neg_address = bx.neg(address);
let offset = bx.and(neg_address, align_minus_1);
let dst = bx.inbounds_ptradd(alloca, offset);
bx.memcpy(dst, min_align, llptr, min_align, size, MemFlags::empty());
// Store the allocated region and the extra to the indirect place.
let indirect_operand = OperandValue::Pair(dst, llextra);
indirect_operand.store(bx, indirect_dest);
}
}
impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {