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use ptradd for vtable indexing

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Like field offsets, these are always constant.
This commit is contained in:
Erik Desjardins 2024-03-10 22:38:53 -04:00
parent 76ee6fc926
commit a7cd803d02
4 changed files with 104 additions and 17 deletions
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13
compiler/rustc_codegen_ssa/src/base.rs
View File

@ -165,14 +165,11 @@ pub fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
cx.tcx().vtable_trait_upcasting_coercion_new_vptr_slot((source, target));
if let Some(entry_idx) = vptr_entry_idx {
let ptr_ty = cx.type_ptr();
let ptr_align = cx.tcx().data_layout.pointer_align.abi;
let gep = bx.inbounds_gep(
ptr_ty,
old_info,
&[bx.const_usize(u64::try_from(entry_idx).unwrap())],
);
let new_vptr = bx.load(ptr_ty, gep, ptr_align);
let ptr_size = bx.data_layout().pointer_size;
let ptr_align = bx.data_layout().pointer_align.abi;
let vtable_byte_offset = u64::try_from(entry_idx).unwrap() * ptr_size.bytes();
let gep = bx.inbounds_ptradd(old_info, bx.const_usize(vtable_byte_offset));
let new_vptr = bx.load(bx.type_ptr(), gep, ptr_align);
bx.nonnull_metadata(new_vptr);
// VTable loads are invariant.
bx.set_invariant_load(new_vptr);

19
compiler/rustc_codegen_ssa/src/meth.rs
View File

@ -20,9 +20,13 @@ impl<'a, 'tcx> VirtualIndex {
ty: Ty<'tcx>,
fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
) -> Bx::Value {
// Load the data pointer from the object.
// Load the function pointer from the object.
debug!("get_fn({llvtable:?}, {ty:?}, {self:?})");
let llty = bx.fn_ptr_backend_type(fn_abi);
let ptr_size = bx.data_layout().pointer_size;
let ptr_align = bx.data_layout().pointer_align.abi;
let vtable_byte_offset = self.0 * ptr_size.bytes();
if bx.cx().sess().opts.unstable_opts.virtual_function_elimination
&& bx.cx().sess().lto() == Lto::Fat
@ -30,12 +34,10 @@ impl<'a, 'tcx> VirtualIndex {
let typeid = bx
.typeid_metadata(typeid_for_trait_ref(bx.tcx(), expect_dyn_trait_in_self(ty)))
.unwrap();
let vtable_byte_offset = self.0 * bx.data_layout().pointer_size.bytes();
let func = bx.type_checked_load(llvtable, vtable_byte_offset, typeid);
func
} else {
let ptr_align = bx.tcx().data_layout.pointer_align.abi;
let gep = bx.inbounds_gep(llty, llvtable, &[bx.const_usize(self.0)]);
let gep = bx.inbounds_ptradd(llvtable, bx.const_usize(vtable_byte_offset));
let ptr = bx.load(llty, gep, ptr_align);
bx.nonnull_metadata(ptr);
// VTable loads are invariant.
@ -53,9 +55,12 @@ impl<'a, 'tcx> VirtualIndex {
debug!("get_int({:?}, {:?})", llvtable, self);
let llty = bx.type_isize();
let usize_align = bx.tcx().data_layout.pointer_align.abi;
let gep = bx.inbounds_gep(llty, llvtable, &[bx.const_usize(self.0)]);
let ptr = bx.load(llty, gep, usize_align);
let ptr_size = bx.data_layout().pointer_size;
let ptr_align = bx.data_layout().pointer_align.abi;
let vtable_byte_offset = self.0 * ptr_size.bytes();
let gep = bx.inbounds_ptradd(llvtable, bx.const_usize(vtable_byte_offset));
let ptr = bx.load(llty, gep, ptr_align);
// VTable loads are invariant.
bx.set_invariant_load(ptr);
ptr

4
tests/codegen/dst-offset.rs
View File

@ -25,9 +25,9 @@ struct Dst<T: ?Sized> {
pub fn dst_dyn_trait_offset(s: &Dst<dyn Drop>) -> &dyn Drop {
// The alignment of dyn trait is unknown, so we compute the offset based on align from the vtable.
// CHECK: [[SIZE_PTR:%[0-9]+]] = getelementptr inbounds {{.+}} [[VTABLE_PTR]]
// CHECK: [[SIZE_PTR:%[0-9]+]] = getelementptr inbounds i8, ptr [[VTABLE_PTR]]
// CHECK: load [[USIZE]], ptr [[SIZE_PTR]]
// CHECK: [[ALIGN_PTR:%[0-9]+]] = getelementptr inbounds {{.+}} [[VTABLE_PTR]]
// CHECK: [[ALIGN_PTR:%[0-9]+]] = getelementptr inbounds i8, ptr [[VTABLE_PTR]]
// CHECK: load [[USIZE]], ptr [[ALIGN_PTR]]
// CHECK: getelementptr inbounds i8, ptr [[DATA_PTR]]

85
tests/codegen/vtable-upcast.rs Normal file
View File

@ -0,0 +1,85 @@
//! This file tests that we correctly generate GEP instructions for vtable upcasting.
//@ compile-flags: -C no-prepopulate-passes -Copt-level=0
#![crate_type = "lib"]
#![feature(trait_upcasting)]
pub trait Base {
fn base(&self);
}
pub trait A : Base {
fn a(&self);
}
pub trait B : Base {
fn b(&self);
}
pub trait Diamond : A + B {
fn diamond(&self);
}
// CHECK-LABEL: upcast_a_to_base
#[no_mangle]
pub fn upcast_a_to_base(x: &dyn A) -> &dyn Base {
// Requires no adjustment, since its vtable is extended from `Base`.
// CHECK: start:
// CHECK-NEXT: insertvalue
// CHECK-NEXT: insertvalue
// CHECK-NEXT: ret
x as &dyn Base
}
// CHECK-LABEL: upcast_b_to_base
#[no_mangle]
pub fn upcast_b_to_base(x: &dyn B) -> &dyn Base {
// Requires no adjustment, since its vtable is extended from `Base`.
// CHECK: start:
// CHECK-NEXT: insertvalue
// CHECK-NEXT: insertvalue
// CHECK-NEXT: ret
x as &dyn Base
}
// CHECK-LABEL: upcast_diamond_to_a
#[no_mangle]
pub fn upcast_diamond_to_a(x: &dyn Diamond) -> &dyn A {
// Requires no adjustment, since its vtable is extended from `A` (as the first supertrait).
// CHECK: start:
// CHECK-NEXT: insertvalue
// CHECK-NEXT: insertvalue
// CHECK-NEXT: ret
x as &dyn A
}
// CHECK-LABEL: upcast_diamond_to_b
// CHECK-SAME: (ptr align {{[0-9]+}} [[DATA_PTR:%.+]], ptr align {{[0-9]+}} [[VTABLE_PTR:%.+]])
#[no_mangle]
pub fn upcast_diamond_to_b(x: &dyn Diamond) -> &dyn B {
// Requires adjustment, since it's a non-first supertrait.
// CHECK: start:
// CHECK-NEXT: [[UPCAST_SLOT_PTR:%.+]] = getelementptr inbounds i8, ptr [[VTABLE_PTR]]
// CHECK-NEXT: [[UPCAST_VTABLE_PTR:%.+]] = load ptr, ptr [[UPCAST_SLOT_PTR]]
// CHECK-NEXT: [[FAT_PTR_1:%.+]] = insertvalue { ptr, ptr } poison, ptr [[DATA_PTR]], 0
// CHECK-NEXT: [[FAT_PTR_2:%.+]] = insertvalue { ptr, ptr } [[FAT_PTR_1]], ptr [[UPCAST_VTABLE_PTR]], 1
// CHECK-NEXT: ret { ptr, ptr } [[FAT_PTR_2]]
x as &dyn B
}
// CHECK-LABEL: upcast_diamond_to_b
#[no_mangle]
pub fn upcast_diamond_to_base(x: &dyn Diamond) -> &dyn Base {
// Requires no adjustment, since `Base` is the first supertrait of `A`,
// which is the first supertrait of `Diamond`.
// CHECK: start:
// CHECK-NEXT: insertvalue
// CHECK-NEXT: insertvalue
// CHECK-NEXT: ret
x as &dyn Base
}