OpenE2K
/
rust
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Auto merge of #73453 - erikdesjardins:tuplayout, r=eddyb 

Ignore ZST offsets when deciding whether to use Scalar/ScalarPair layout

This is important because Scalar/ScalarPair layout previously would not be used if any ZST had nonzero offset.
For example, before this change, only `((), u128)` would be laid out like `u128`, not `(u128, ())`.

Fixes #63244
This commit is contained in:
bors 2020-09-25 14:42:20 +00:00
parent b984ef6797 24e0913e37
commit 5b9e886403
7 changed files with 230 additions and 76 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
compiler/rustc_codegen_ssa/src/mir/place.rs
View File

@ -93,15 +93,33 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
let effective_field_align = self.align.restrict_for_offset(offset);
let mut simple = || {
// Unions and newtypes only use an offset of 0.
let llval = if offset.bytes() == 0 {
self.llval
} else if let Abi::ScalarPair(ref a, ref b) = self.layout.abi {
// Offsets have to match either first or second field.
assert_eq!(offset, a.value.size(bx.cx()).align_to(b.value.align(bx.cx()).abi));
bx.struct_gep(self.llval, 1)
} else {
bx.struct_gep(self.llval, bx.cx().backend_field_index(self.layout, ix))
let llval = match self.layout.abi {
_ if offset.bytes() == 0 => {
// Unions and newtypes only use an offset of 0.
// Also handles the first field of Scalar, ScalarPair, and Vector layouts.
self.llval
}
Abi::ScalarPair(ref a, ref b)
if offset == a.value.size(bx.cx()).align_to(b.value.align(bx.cx()).abi) =>
{
// Offset matches second field.
bx.struct_gep(self.llval, 1)
}
Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } if field.is_zst() => {
// ZST fields are not included in Scalar, ScalarPair, and Vector layouts, so manually offset the pointer.
let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
bx.gep(byte_ptr, &[bx.const_usize(offset.bytes())])
}
Abi::Scalar(_) | Abi::ScalarPair(..) => {
// All fields of Scalar and ScalarPair layouts must have been handled by this point.
// Vector layouts have additional fields for each element of the vector, so don't panic in that case.
bug!(
"offset of non-ZST field `{:?}` does not match layout `{:#?}`",
field,
self.layout
);
}
_ => bx.struct_gep(self.llval, bx.cx().backend_field_index(self.layout, ix)),
};
PlaceRef {
// HACK(eddyb): have to bitcast pointers until LLVM removes pointee types.

116
compiler/rustc_middle/src/ty/layout.rs
View File

@ -390,78 +390,60 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
// Unpack newtype ABIs and find scalar pairs.
if sized && size.bytes() > 0 {
// All other fields must be ZSTs, and we need them to all start at 0.
let mut zst_offsets = offsets.iter().enumerate().filter(|&(i, _)| fields[i].is_zst());
if zst_offsets.all(|(_, o)| o.bytes() == 0) {
let mut non_zst_fields = fields.iter().enumerate().filter(|&(_, f)| !f.is_zst());
// All other fields must be ZSTs.
let mut non_zst_fields = fields.iter().enumerate().filter(|&(_, f)| !f.is_zst());
match (non_zst_fields.next(), non_zst_fields.next(), non_zst_fields.next()) {
// We have exactly one non-ZST field.
(Some((i, field)), None, None) => {
// Field fills the struct and it has a scalar or scalar pair ABI.
if offsets[i].bytes() == 0
&& align.abi == field.align.abi
&& size == field.size
{
match field.abi {
// For plain scalars, or vectors of them, we can't unpack
// newtypes for `#[repr(C)]`, as that affects C ABIs.
Abi::Scalar(_) | Abi::Vector { .. } if optimize => {
abi = field.abi.clone();
}
// But scalar pairs are Rust-specific and get
// treated as aggregates by C ABIs anyway.
Abi::ScalarPair(..) => {
abi = field.abi.clone();
}
_ => {}
match (non_zst_fields.next(), non_zst_fields.next(), non_zst_fields.next()) {
// We have exactly one non-ZST field.
(Some((i, field)), None, None) => {
// Field fills the struct and it has a scalar or scalar pair ABI.
if offsets[i].bytes() == 0 && align.abi == field.align.abi && size == field.size
{
match field.abi {
// For plain scalars, or vectors of them, we can't unpack
// newtypes for `#[repr(C)]`, as that affects C ABIs.
Abi::Scalar(_) | Abi::Vector { .. } if optimize => {
abi = field.abi.clone();
}
// But scalar pairs are Rust-specific and get
// treated as aggregates by C ABIs anyway.
Abi::ScalarPair(..) => {
abi = field.abi.clone();
}
_ => {}
}
}
// Two non-ZST fields, and they're both scalars.
(
Some((
i,
&TyAndLayout {
layout: &Layout { abi: Abi::Scalar(ref a), .. }, ..
},
)),
Some((
j,
&TyAndLayout {
layout: &Layout { abi: Abi::Scalar(ref b), .. }, ..
},
)),
None,
) => {
// Order by the memory placement, not source order.
let ((i, a), (j, b)) = if offsets[i] < offsets[j] {
((i, a), (j, b))
} else {
((j, b), (i, a))
};
let pair = self.scalar_pair(a.clone(), b.clone());
let pair_offsets = match pair.fields {
FieldsShape::Arbitrary { ref offsets, ref memory_index } => {
assert_eq!(memory_index, &[0, 1]);
offsets
}
_ => bug!(),
};
if offsets[i] == pair_offsets[0]
&& offsets[j] == pair_offsets[1]
&& align == pair.align
&& size == pair.size
{
// We can use `ScalarPair` only when it matches our
// already computed layout (including `#[repr(C)]`).
abi = pair.abi;
}
}
_ => {}
}
// Two non-ZST fields, and they're both scalars.
(
Some((i, &TyAndLayout { layout: &Layout { abi: Abi::Scalar(ref a), .. }, .. })),
Some((j, &TyAndLayout { layout: &Layout { abi: Abi::Scalar(ref b), .. }, .. })),
None,
) => {
// Order by the memory placement, not source order.
let ((i, a), (j, b)) =
if offsets[i] < offsets[j] { ((i, a), (j, b)) } else { ((j, b), (i, a)) };
let pair = self.scalar_pair(a.clone(), b.clone());
let pair_offsets = match pair.fields {
FieldsShape::Arbitrary { ref offsets, ref memory_index } => {
assert_eq!(memory_index, &[0, 1]);
offsets
}
_ => bug!(),
};
if offsets[i] == pair_offsets[0]
&& offsets[j] == pair_offsets[1]
&& align == pair.align
&& size == pair.size
{
// We can use `ScalarPair` only when it matches our
// already computed layout (including `#[repr(C)]`).
abi = pair.abi;
}
}
_ => {}
}
}

36
src/test/codegen/tuple-layout-opt.rs Normal file
View File

@ -0,0 +1,36 @@
// ignore-emscripten
// compile-flags: -C no-prepopulate-passes
// Test that tuples get optimized layout, in particular with a ZST in the last field (#63244)
#![crate_type="lib"]
type ScalarZstLast = (u128, ());
// CHECK: define i128 @test_ScalarZstLast(i128 %_1)
#[no_mangle]
pub fn test_ScalarZstLast(_: ScalarZstLast) -> ScalarZstLast { loop {} }
type ScalarZstFirst = ((), u128);
// CHECK: define i128 @test_ScalarZstFirst(i128 %_1)
#[no_mangle]
pub fn test_ScalarZstFirst(_: ScalarZstFirst) -> ScalarZstFirst { loop {} }
type ScalarPairZstLast = (u8, u128, ());
// CHECK: define { i128, i8 } @test_ScalarPairZstLast(i128 %_1.0, i8 %_1.1)
#[no_mangle]
pub fn test_ScalarPairZstLast(_: ScalarPairZstLast) -> ScalarPairZstLast { loop {} }
type ScalarPairZstFirst = ((), u8, u128);
// CHECK: define { i8, i128 } @test_ScalarPairZstFirst(i8 %_1.0, i128 %_1.1)
#[no_mangle]
pub fn test_ScalarPairZstFirst(_: ScalarPairZstFirst) -> ScalarPairZstFirst { loop {} }
type ScalarPairLotsOfZsts = ((), u8, (), u128, ());
// CHECK: define { i128, i8 } @test_ScalarPairLotsOfZsts(i128 %_1.0, i8 %_1.1)
#[no_mangle]
pub fn test_ScalarPairLotsOfZsts(_: ScalarPairLotsOfZsts) -> ScalarPairLotsOfZsts { loop {} }
type ScalarPairLottaNesting = (((), ((), u8, (), u128, ())), ());
// CHECK: define { i128, i8 } @test_ScalarPairLottaNesting(i128 %_1.0, i8 %_1.1)
#[no_mangle]
pub fn test_ScalarPairLottaNesting(_: ScalarPairLottaNesting) -> ScalarPairLottaNesting { loop {} }

43
src/test/codegen/zst-offset.rs Normal file
View File

@ -0,0 +1,43 @@
// compile-flags: -C no-prepopulate-passes
#![crate_type = "lib"]
#![feature(repr_simd)]
// Hack to get the correct size for the length part in slices
// CHECK: @helper([[USIZE:i[0-9]+]] %_1)
#[no_mangle]
pub fn helper(_: usize) {
}
// Check that we correctly generate a GEP for a ZST that is not included in Scalar layout
// CHECK-LABEL: @scalar_layout
#[no_mangle]
pub fn scalar_layout(s: &(u64, ())) {
// CHECK: [[X0:%[0-9]+]] = bitcast i64* %s to i8*
// CHECK-NEXT: [[X1:%[0-9]+]] = getelementptr i8, i8* [[X0]], [[USIZE]] 8
let x = &s.1;
&x; // keep variable in an alloca
}
// Check that we correctly generate a GEP for a ZST that is not included in ScalarPair layout
// CHECK-LABEL: @scalarpair_layout
#[no_mangle]
pub fn scalarpair_layout(s: &(u64, u32, ())) {
// CHECK: [[X0:%[0-9]+]] = bitcast { i64, i32 }* %s to i8*
// CHECK-NEXT: [[X1:%[0-9]+]] = getelementptr i8, i8* [[X0]], [[USIZE]] 12
let x = &s.2;
&x; // keep variable in an alloca
}
#[repr(simd)]
pub struct U64x4(u64, u64, u64, u64);
// Check that we correctly generate a GEP for a ZST that is not included in Vector layout
// CHECK-LABEL: @vector_layout
#[no_mangle]
pub fn vector_layout(s: &(U64x4, ())) {
// CHECK: [[X0:%[0-9]+]] = bitcast <4 x i64>* %s to i8*
// CHECK-NEXT: [[X1:%[0-9]+]] = getelementptr i8, i8* [[X0]], [[USIZE]] 32
let x = &s.1;
&x; // keep variable in an alloca
}

26
src/test/ui/dynamically-sized-types/dst-tuple-no-reorder.rs Normal file
View File

@ -0,0 +1,26 @@
// run-pass
#![feature(unsized_tuple_coercion)]
// Ensure that unsizable fields that might be accessed don't get reordered
fn nonzero_size() {
let sized: (u8, [u32; 2]) = (123, [456, 789]);
let unsize: &(u8, [u32]) = &sized;
assert_eq!(unsize.0, 123);
assert_eq!(unsize.1.len(), 2);
assert_eq!(unsize.1[0], 456);
assert_eq!(unsize.1[1], 789);
}
fn zst() {
let sized: (u8, [u32; 0]) = (123, []);
let unsize: &(u8, [u32]) = &sized;
assert_eq!(unsize.0, 123);
assert_eq!(unsize.1.len(), 0);
}
pub fn main() {
nonzero_size();
zst();
}

22
src/test/ui/dynamically-sized-types/dst-tuple-zst-offsets.rs Normal file
View File

@ -0,0 +1,22 @@
// run-pass
#![feature(unsized_tuple_coercion)]
// Check that we do not change the offsets of ZST fields when unsizing
fn scalar_layout() {
let sized: &(u8, [(); 13]) = &(123, [(); 13]);
let unsize: &(u8, [()]) = sized;
assert_eq!(sized.1.as_ptr(), unsize.1.as_ptr());
}
fn scalarpair_layout() {
let sized: &(u8, u16, [(); 13]) = &(123, 456, [(); 13]);
let unsize: &(u8, u16, [()]) = sized;
assert_eq!(sized.2.as_ptr(), unsize.2.as_ptr());
}
pub fn main() {
scalar_layout();
scalarpair_layout();
}

27
src/test/ui/mir/mir_const_prop_tuple_field_reorder.rs Normal file
View File

@ -0,0 +1,27 @@
// compile-flags: -Z mir-opt-level=2
// build-pass
#![crate_type="lib"]
// This used to ICE: const-prop did not account for field reordering of scalar pairs,
// and would generate a tuple like `(0x1337, VariantBar): (FooEnum, isize)`,
// causing assertion failures in codegen when trying to read 0x1337 at the wrong type.
pub enum FooEnum {
VariantBar,
VariantBaz,
VariantBuz,
}
pub fn wrong_index() -> isize {
let (_, b) = id((FooEnum::VariantBar, 0x1337));
b
}
pub fn wrong_index_two() -> isize {
let (_, (_, b)) = id(((), (FooEnum::VariantBar, 0x1338)));
b
}
fn id<T>(x: T) -> T {
x
}