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Make SSA aggregates without needing an alloca

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This commit is contained in:
Scott McMurray 2024-04-14 00:51:49 -07:00
parent 7448c24e02
commit c38f75c21f
5 changed files with 203 additions and 28 deletions
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2
Cargo.lock
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@ -3746,8 +3746,10 @@ name = "rustc_codegen_ssa"
version = "0.0.0"
dependencies = [
"ar_archive_writer",
"arrayvec",
"bitflags 2.5.0",
"cc",
"either",
"itertools 0.12.1",
"jobserver",
"libc",

4
compiler/rustc_codegen_ssa/Cargo.toml
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@ -6,8 +6,10 @@ edition = "2021"
[dependencies]
# tidy-alphabetical-start
ar_archive_writer = "0.2.0"
arrayvec = { version = "0.7", default-features = false }
bitflags = "2.4.1"
cc = "1.0.97"
cc = "1.0.90"
either = "1.5.0"
itertools = "0.12"
jobserver = "0.1.28"
pathdiff = "0.2.0"

30
compiler/rustc_codegen_ssa/src/mir/operand.rs
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@ -14,6 +14,9 @@ use rustc_target::abi::{self, Abi, Align, Size};
use std::fmt;
use arrayvec::ArrayVec;
use either::Either;
/// The representation of a Rust value. The enum variant is in fact
/// uniquely determined by the value's type, but is kept as a
/// safety check.
@ -58,6 +61,33 @@ pub enum OperandValue<V> {
ZeroSized,
}
impl<V> OperandValue<V> {
/// If this is ZeroSized/Immediate/Pair, return an array of the 0/1/2 values.
/// If this is Ref, return the place.
#[inline]
pub fn immediates_or_place(self) -> Either<ArrayVec<V, 2>, PlaceValue<V>> {
match self {
OperandValue::ZeroSized => Either::Left(ArrayVec::new()),
OperandValue::Immediate(a) => Either::Left(ArrayVec::from_iter([a])),
OperandValue::Pair(a, b) => Either::Left([a, b].into()),
OperandValue::Ref(p) => Either::Right(p),
}
}
/// Given an array of 0/1/2 immediate values, return ZeroSized/Immediate/Pair.
#[inline]
pub fn from_immediates(immediates: ArrayVec<V, 2>) -> Self {
let mut it = immediates.into_iter();
let Some(a) = it.next() else {
return OperandValue::ZeroSized;
};
let Some(b) = it.next() else {
return OperandValue::Immediate(a);
};
OperandValue::Pair(a, b)
}
}
/// An `OperandRef` is an "SSA" reference to a Rust value, along with
/// its type.
///

81
compiler/rustc_codegen_ssa/src/mir/rvalue.rs
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@ -8,14 +8,16 @@ use crate::traits::*;
use crate::MemFlags;
use rustc_hir as hir;
use rustc_middle::mir::{self, AggregateKind, Operand};
use rustc_middle::mir;
use rustc_middle::ty::cast::{CastTy, IntTy};
use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, adjustment::PointerCoercion, Instance, Ty, TyCtxt};
use rustc_middle::{bug, span_bug};
use rustc_session::config::OptLevel;
use rustc_span::{Span, DUMMY_SP};
use rustc_target::abi::{self, FIRST_VARIANT};
use rustc_target::abi::{self, FieldIdx, FIRST_VARIANT};
use arrayvec::ArrayVec;
impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
#[instrument(level = "trace", skip(self, bx))]
@ -581,7 +583,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
self.codegen_place_to_pointer(bx, place, mk_ref)
}
mir::Rvalue::CopyForDeref(place) => self.codegen_operand(bx, &Operand::Copy(place)),
mir::Rvalue::CopyForDeref(place) => {
self.codegen_operand(bx, &mir::Operand::Copy(place))
}
mir::Rvalue::AddressOf(mutability, place) => {
let mk_ptr =
move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| Ty::new_ptr(tcx, ty, mutability);
@ -739,11 +743,40 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
}
mir::Rvalue::Repeat(..) => bug!("{rvalue:?} in codegen_rvalue_operand"),
mir::Rvalue::Aggregate(..) => {
// According to `rvalue_creates_operand`, only ZST
// aggregate rvalues are allowed to be operands.
mir::Rvalue::Aggregate(_, ref fields) => {
let ty = rvalue.ty(self.mir, self.cx.tcx());
OperandRef::zero_sized(self.cx.layout_of(self.monomorphize(ty)))
let ty = self.monomorphize(ty);
let layout = self.cx.layout_of(ty);
// `rvalue_creates_operand` has arranged that we only get here if
// we can build the aggregate immediate from the field immediates.
let mut inputs = ArrayVec::<Bx::Value, 2>::new();
let mut input_scalars = ArrayVec::<abi::Scalar, 2>::new();
for field_idx in layout.fields.index_by_increasing_offset() {
let field_idx = FieldIdx::from_usize(field_idx);
let op = self.codegen_operand(bx, &fields[field_idx]);
let values = op.val.immediates_or_place().left_or_else(|p| {
bug!("Field {field_idx:?} is {p:?} making {layout:?}");
});
inputs.extend(values);
let scalars = self.value_kind(op.layout).scalars().unwrap();
input_scalars.extend(scalars);
}
let output_scalars = self.value_kind(layout).scalars().unwrap();
itertools::izip!(&mut inputs, input_scalars, output_scalars).for_each(
|(v, in_s, out_s)| {
if in_s != out_s {
// We have to be really careful about bool here, because
// `(bool,)` stays i1 but `Cell<bool>` becomes i8.
*v = bx.from_immediate(*v);
*v = bx.to_immediate_scalar(*v, out_s);
}
},
);
let val = OperandValue::from_immediates(inputs);
OperandRef { val, layout }
}
mir::Rvalue::ShallowInitBox(ref operand, content_ty) => {
let operand = self.codegen_operand(bx, operand);
@ -1051,16 +1084,29 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
mir::Rvalue::ThreadLocalRef(_) |
mir::Rvalue::Use(..) => // (*)
true,
// This always produces a `ty::RawPtr`, so will be Immediate or Pair
mir::Rvalue::Aggregate(box AggregateKind::RawPtr(..), ..) => true,
// Arrays are always aggregates, so it's not worth checking anything here.
// (If it's really `[(); N]` or `[T; 0]` and we use the place path, fine.)
mir::Rvalue::Repeat(..) => false,
mir::Rvalue::Aggregate(..) => {
mir::Rvalue::Aggregate(ref kind, _) => {
let allowed_kind = match **kind {
// This always produces a `ty::RawPtr`, so will be Immediate or Pair
mir::AggregateKind::RawPtr(..) => true,
mir::AggregateKind::Array(..) => false,
mir::AggregateKind::Tuple => true,
mir::AggregateKind::Adt(def_id, ..) => {
let adt_def = self.cx.tcx().adt_def(def_id);
adt_def.is_struct() && !adt_def.repr().simd()
}
mir::AggregateKind::Closure(..) => true,
// FIXME: Can we do this for simple coroutines too?
mir::AggregateKind::Coroutine(..) | mir::AggregateKind::CoroutineClosure(..) => false,
};
allowed_kind && {
let ty = rvalue.ty(self.mir, self.cx.tcx());
let ty = self.monomorphize(ty);
// For ZST this can be `OperandValueKind::ZeroSized`.
self.cx.spanned_layout_of(ty, span).is_zst()
let layout = self.cx.spanned_layout_of(ty, span);
!self.cx.is_backend_ref(layout)
}
}
}
@ -1102,3 +1148,14 @@ enum OperandValueKind {
Pair(abi::Scalar, abi::Scalar),
ZeroSized,
}
impl OperandValueKind {
fn scalars(self) -> Option<ArrayVec<abi::Scalar, 2>> {
Some(match self {
OperandValueKind::ZeroSized => ArrayVec::new(),
OperandValueKind::Immediate(a) => ArrayVec::from_iter([a]),
OperandValueKind::Pair(a, b) => [a, b].into(),
OperandValueKind::Ref => return None,
})
}
}

114
tests/codegen/mir-aggregate-no-alloca.rs
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@ -1,17 +1,15 @@
//@ compile-flags: -O -C no-prepopulate-passes
//@ compile-flags: -O -C no-prepopulate-passes -Z randomize-layout=no
#![crate_type = "lib"]
#[repr(transparent)]
struct Transparent32(u32);
pub struct Transparent32(u32);
// CHECK: i32 @make_transparent(i32 noundef %x)
#[no_mangle]
pub fn make_transparent(x: u32) -> Transparent32 {
// CHECK: %a = alloca i32
// CHECK: store i32 %x, ptr %a
// CHECK: %[[TEMP:.+]] = load i32, ptr %a
// CHECK: ret i32 %[[TEMP]]
// CHECK-NOT: alloca
// CHECK: ret i32 %x
let a = Transparent32(x);
a
}
@ -19,21 +17,107 @@ pub fn make_transparent(x: u32) -> Transparent32 {
// CHECK: i32 @make_closure(i32 noundef %x)
#[no_mangle]
pub fn make_closure(x: i32) -> impl Fn(i32) -> i32 {
// CHECK: %[[ALLOCA:.+]] = alloca i32
// CHECK: store i32 %x, ptr %[[ALLOCA]]
// CHECK: %[[TEMP:.+]] = load i32, ptr %[[ALLOCA]]
// CHECK: ret i32 %[[TEMP]]
// CHECK-NOT: alloca
// CHECK: ret i32 %x
move |y| x + y
}
#[repr(transparent)]
pub struct TransparentPair((), (u16, u16), ());
// CHECK: { i16, i16 } @make_transparent_pair(i16 noundef %x.0, i16 noundef %x.1)
#[no_mangle]
pub fn make_transparent_pair(x: (u16, u16)) -> TransparentPair {
// CHECK-NOT: alloca
// CHECK: %[[TEMP0:.+]] = insertvalue { i16, i16 } poison, i16 %x.0, 0
// CHECK: %[[TEMP1:.+]] = insertvalue { i16, i16 } %[[TEMP0]], i16 %x.1, 1
// CHECK: ret { i16, i16 } %[[TEMP1]]
let a = TransparentPair((), x, ());
a
}
// CHECK-LABEL: { i32, i32 } @make_2_tuple(i32 noundef %x)
#[no_mangle]
pub fn make_2_tuple(x: u32) -> (u32, u32) {
// CHECK: %pair = alloca { i32, i32 }
// CHECK: store i32
// CHECK: store i32
// CHECK: load i32
// CHECK: load i32
// CHECK-NOT: alloca
// CHECK: %[[TEMP0:.+]] = insertvalue { i32, i32 } poison, i32 %x, 0
// CHECK: %[[TEMP1:.+]] = insertvalue { i32, i32 } %[[TEMP0]], i32 %x, 1
// CHECK: ret { i32, i32 } %[[TEMP1]]
let pair = (x, x);
pair
}
// CHECK-LABEL: i8 @make_cell_of_bool(i1 noundef zeroext %b)
#[no_mangle]
pub fn make_cell_of_bool(b: bool) -> std::cell::Cell<bool> {
// CHECK: %[[BYTE:.+]] = zext i1 %b to i8
// CHECK: ret i8 %[[BYTE]]
std::cell::Cell::new(b)
}
// CHECK-LABLE: { i8, i16 } @make_cell_of_bool_and_short(i1 noundef zeroext %b, i16 noundef %s)
#[no_mangle]
pub fn make_cell_of_bool_and_short(b: bool, s: u16) -> std::cell::Cell<(bool, u16)> {
// CHECK-NOT: alloca
// CHECK: %[[BYTE:.+]] = zext i1 %b to i8
// CHECK: %[[TEMP0:.+]] = insertvalue { i8, i16 } poison, i8 %[[BYTE]], 0
// CHECK: %[[TEMP1:.+]] = insertvalue { i8, i16 } %[[TEMP0]], i16 %s, 1
// CHECK: ret { i8, i16 } %[[TEMP1]]
std::cell::Cell::new((b, s))
}
// CHECK-LABEL: { i1, i1 } @make_tuple_of_bools(i1 noundef zeroext %a, i1 noundef zeroext %b)
#[no_mangle]
pub fn make_tuple_of_bools(a: bool, b: bool) -> (bool, bool) {
// CHECK-NOT: alloca
// CHECK: %[[TEMP0:.+]] = insertvalue { i1, i1 } poison, i1 %a, 0
// CHECK: %[[TEMP1:.+]] = insertvalue { i1, i1 } %[[TEMP0]], i1 %b, 1
// CHECK: ret { i1, i1 } %[[TEMP1]]
(a, b)
}
pub struct Struct0();
// CHECK-LABEL: void @make_struct_0()
#[no_mangle]
pub fn make_struct_0() -> Struct0 {
// CHECK: ret void
let s = Struct0();
s
}
pub struct Struct1(i32);
// CHECK-LABEL: i32 @make_struct_1(i32 noundef %a)
#[no_mangle]
pub fn make_struct_1(a: i32) -> Struct1 {
// CHECK: ret i32 %a
let s = Struct1(a);
s
}
pub struct Struct2Asc(i16, i64);
// CHECK-LABEL: { i64, i16 } @make_struct_2_asc(i16 noundef %a, i64 noundef %b)
#[no_mangle]
pub fn make_struct_2_asc(a: i16, b: i64) -> Struct2Asc {
// CHECK-NOT: alloca
// CHECK: %[[TEMP0:.+]] = insertvalue { i64, i16 } poison, i64 %b, 0
// CHECK: %[[TEMP1:.+]] = insertvalue { i64, i16 } %[[TEMP0]], i16 %a, 1
// CHECK: ret { i64, i16 } %[[TEMP1]]
let s = Struct2Asc(a, b);
s
}
pub struct Struct2Desc(i64, i16);
// CHECK-LABEL: { i64, i16 } @make_struct_2_desc(i64 noundef %a, i16 noundef %b)
#[no_mangle]
pub fn make_struct_2_desc(a: i64, b: i16) -> Struct2Desc {
// CHECK-NOT: alloca
// CHECK: %[[TEMP0:.+]] = insertvalue { i64, i16 } poison, i64 %a, 0
// CHECK: %[[TEMP1:.+]] = insertvalue { i64, i16 } %[[TEMP0]], i16 %b, 1
// CHECK: ret { i64, i16 } %[[TEMP1]]
let s = Struct2Desc(a, b);
s
}