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Align unsized locals

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Allocate an extra space for unsized locals and manually align the
storage, since alloca doesn't support dynamic alignment.
This commit is contained in:
Tomasz Miąsko 2023-05-08 00:00:00 +00:00
parent ce042889f7
commit 83a5a69a4c
2 changed files with 45 additions and 11 deletions
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26
compiler/rustc_codegen_ssa/src/mir/operand.rs
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@ -402,8 +402,6 @@ impl<'a, 'tcx, V: CodegenObject> OperandValue<V> {
indirect_dest: PlaceRef<'tcx, V>,
) {
debug!("OperandRef::store_unsized: operand={:?}, indirect_dest={:?}", self, indirect_dest);
let flags = MemFlags::empty();
// `indirect_dest` must have `*mut T` type. We extract `T` out of it.
let unsized_ty = indirect_dest
.layout
@ -416,17 +414,23 @@ impl<'a, 'tcx, V: CodegenObject> OperandValue<V> {
bug!("store_unsized called with a sized value")
};
// FIXME: choose an appropriate alignment, or use dynamic align somehow
let max_align = Align::from_bits(128).unwrap();
let min_align = Align::from_bits(8).unwrap();
// Allocate an appropriate region on the stack, and copy the value into it
let (llsize, _) = glue::size_and_align_of_dst(bx, unsized_ty, Some(llextra));
let lldst = bx.byte_array_alloca(llsize, max_align);
bx.memcpy(lldst, max_align, llptr, min_align, llsize, flags);
// 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) = glue::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.byte_array_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_gep(bx.type_i8(), 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(lldst, llextra);
let indirect_operand = OperandValue::Pair(dst, llextra);
indirect_operand.store(bx, indirect_dest);
}
}