rust/src/constant.rs
2022-01-18 12:49:50 +01:00

552 lines
22 KiB
Rust

//! Handling of `static`s, `const`s and promoted allocations
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::ErrorReported;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use rustc_middle::mir::interpret::{
read_target_uint, AllocId, Allocation, ConstValue, ErrorHandled, GlobalAlloc, Scalar,
};
use rustc_middle::ty::ConstKind;
use rustc_span::DUMMY_SP;
use cranelift_codegen::ir::GlobalValueData;
use cranelift_module::*;
use crate::prelude::*;
pub(crate) struct ConstantCx {
todo: Vec<TodoItem>,
done: FxHashSet<DataId>,
anon_allocs: FxHashMap<AllocId, DataId>,
}
#[derive(Copy, Clone, Debug)]
enum TodoItem {
Alloc(AllocId),
Static(DefId),
}
impl ConstantCx {
pub(crate) fn new() -> Self {
ConstantCx { todo: vec![], done: FxHashSet::default(), anon_allocs: FxHashMap::default() }
}
pub(crate) fn finalize(mut self, tcx: TyCtxt<'_>, module: &mut dyn Module) {
//println!("todo {:?}", self.todo);
define_all_allocs(tcx, module, &mut self);
//println!("done {:?}", self.done);
self.done.clear();
}
}
pub(crate) fn check_constants(fx: &mut FunctionCx<'_, '_, '_>) -> bool {
let mut all_constants_ok = true;
for constant in &fx.mir.required_consts {
let const_ = match fx.monomorphize(constant.literal) {
ConstantKind::Ty(ct) => ct,
ConstantKind::Val(..) => continue,
};
match const_.val {
ConstKind::Value(_) => {}
ConstKind::Unevaluated(unevaluated) => {
if let Err(err) =
fx.tcx.const_eval_resolve(ParamEnv::reveal_all(), unevaluated, None)
{
all_constants_ok = false;
match err {
ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {
fx.tcx.sess.span_err(constant.span, "erroneous constant encountered");
}
ErrorHandled::TooGeneric => {
span_bug!(
constant.span,
"codgen encountered polymorphic constant: {:?}",
err
);
}
}
}
}
ConstKind::Param(_)
| ConstKind::Infer(_)
| ConstKind::Bound(_, _)
| ConstKind::Placeholder(_)
| ConstKind::Error(_) => unreachable!("{:?}", const_),
}
}
all_constants_ok
}
pub(crate) fn codegen_static(tcx: TyCtxt<'_>, module: &mut dyn Module, def_id: DefId) {
let mut constants_cx = ConstantCx::new();
constants_cx.todo.push(TodoItem::Static(def_id));
constants_cx.finalize(tcx, module);
}
pub(crate) fn codegen_tls_ref<'tcx>(
fx: &mut FunctionCx<'_, '_, 'tcx>,
def_id: DefId,
layout: TyAndLayout<'tcx>,
) -> CValue<'tcx> {
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
if fx.clif_comments.enabled() {
fx.add_comment(local_data_id, format!("tls {:?}", def_id));
}
let tls_ptr = fx.bcx.ins().tls_value(fx.pointer_type, local_data_id);
CValue::by_val(tls_ptr, layout)
}
fn codegen_static_ref<'tcx>(
fx: &mut FunctionCx<'_, '_, 'tcx>,
def_id: DefId,
layout: TyAndLayout<'tcx>,
) -> CPlace<'tcx> {
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
if fx.clif_comments.enabled() {
fx.add_comment(local_data_id, format!("{:?}", def_id));
}
let global_ptr = fx.bcx.ins().global_value(fx.pointer_type, local_data_id);
assert!(!layout.is_unsized(), "unsized statics aren't supported");
assert!(
matches!(
fx.bcx.func.global_values[local_data_id],
GlobalValueData::Symbol { tls: false, .. }
),
"tls static referenced without Rvalue::ThreadLocalRef"
);
CPlace::for_ptr(crate::pointer::Pointer::new(global_ptr), layout)
}
pub(crate) fn codegen_constant<'tcx>(
fx: &mut FunctionCx<'_, '_, 'tcx>,
constant: &Constant<'tcx>,
) -> CValue<'tcx> {
let const_ = match fx.monomorphize(constant.literal) {
ConstantKind::Ty(ct) => ct,
ConstantKind::Val(val, ty) => return codegen_const_value(fx, val, ty),
};
let const_val = match const_.val {
ConstKind::Value(const_val) => const_val,
ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted })
if fx.tcx.is_static(def.did) =>
{
assert!(substs.is_empty());
assert!(promoted.is_none());
return codegen_static_ref(fx, def.did, fx.layout_of(const_.ty)).to_cvalue(fx);
}
ConstKind::Unevaluated(unevaluated) => {
match fx.tcx.const_eval_resolve(ParamEnv::reveal_all(), unevaluated, None) {
Ok(const_val) => const_val,
Err(_) => {
span_bug!(constant.span, "erroneous constant not captured by required_consts");
}
}
}
ConstKind::Param(_)
| ConstKind::Infer(_)
| ConstKind::Bound(_, _)
| ConstKind::Placeholder(_)
| ConstKind::Error(_) => unreachable!("{:?}", const_),
};
codegen_const_value(fx, const_val, const_.ty)
}
pub(crate) fn codegen_const_value<'tcx>(
fx: &mut FunctionCx<'_, '_, 'tcx>,
const_val: ConstValue<'tcx>,
ty: Ty<'tcx>,
) -> CValue<'tcx> {
let layout = fx.layout_of(ty);
assert!(!layout.is_unsized(), "sized const value");
if layout.is_zst() {
return CValue::by_ref(crate::Pointer::dangling(layout.align.pref), layout);
}
match const_val {
ConstValue::Scalar(x) => match x {
Scalar::Int(int) => {
if fx.clif_type(layout.ty).is_some() {
return CValue::const_val(fx, layout, int);
} else {
let raw_val = int.to_bits(int.size()).unwrap();
let val = match int.size().bytes() {
1 => fx.bcx.ins().iconst(types::I8, raw_val as i64),
2 => fx.bcx.ins().iconst(types::I16, raw_val as i64),
4 => fx.bcx.ins().iconst(types::I32, raw_val as i64),
8 => fx.bcx.ins().iconst(types::I64, raw_val as i64),
16 => {
let lsb = fx.bcx.ins().iconst(types::I64, raw_val as u64 as i64);
let msb =
fx.bcx.ins().iconst(types::I64, (raw_val >> 64) as u64 as i64);
fx.bcx.ins().iconcat(lsb, msb)
}
_ => unreachable!(),
};
let place = CPlace::new_stack_slot(fx, layout);
place.to_ptr().store(fx, val, MemFlags::trusted());
place.to_cvalue(fx)
}
}
Scalar::Ptr(ptr, _size) => {
let (alloc_id, offset) = ptr.into_parts(); // we know the `offset` is relative
let alloc_kind = fx.tcx.get_global_alloc(alloc_id);
let base_addr = match alloc_kind {
Some(GlobalAlloc::Memory(alloc)) => {
let data_id = data_id_for_alloc_id(
&mut fx.constants_cx,
fx.module,
alloc_id,
alloc.mutability,
);
let local_data_id =
fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
if fx.clif_comments.enabled() {
fx.add_comment(local_data_id, format!("{:?}", alloc_id));
}
fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
}
Some(GlobalAlloc::Function(instance)) => {
let func_id = crate::abi::import_function(fx.tcx, fx.module, instance);
let local_func_id =
fx.module.declare_func_in_func(func_id, &mut fx.bcx.func);
fx.bcx.ins().func_addr(fx.pointer_type, local_func_id)
}
Some(GlobalAlloc::Static(def_id)) => {
assert!(fx.tcx.is_static(def_id));
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
let local_data_id =
fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
if fx.clif_comments.enabled() {
fx.add_comment(local_data_id, format!("{:?}", def_id));
}
fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
}
None => bug!("missing allocation {:?}", alloc_id),
};
let val = if offset.bytes() != 0 {
fx.bcx.ins().iadd_imm(base_addr, i64::try_from(offset.bytes()).unwrap())
} else {
base_addr
};
CValue::by_val(val, layout)
}
},
ConstValue::ByRef { alloc, offset } => CValue::by_ref(
pointer_for_allocation(fx, alloc)
.offset_i64(fx, i64::try_from(offset.bytes()).unwrap()),
layout,
),
ConstValue::Slice { data, start, end } => {
let ptr = pointer_for_allocation(fx, data)
.offset_i64(fx, i64::try_from(start).unwrap())
.get_addr(fx);
let len = fx
.bcx
.ins()
.iconst(fx.pointer_type, i64::try_from(end.checked_sub(start).unwrap()).unwrap());
CValue::by_val_pair(ptr, len, layout)
}
}
}
fn pointer_for_allocation<'tcx>(
fx: &mut FunctionCx<'_, '_, 'tcx>,
alloc: &'tcx Allocation,
) -> crate::pointer::Pointer {
let alloc_id = fx.tcx.create_memory_alloc(alloc);
let data_id =
data_id_for_alloc_id(&mut fx.constants_cx, &mut *fx.module, alloc_id, alloc.mutability);
let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
if fx.clif_comments.enabled() {
fx.add_comment(local_data_id, format!("{:?}", alloc_id));
}
let global_ptr = fx.bcx.ins().global_value(fx.pointer_type, local_data_id);
crate::pointer::Pointer::new(global_ptr)
}
pub(crate) fn data_id_for_alloc_id(
cx: &mut ConstantCx,
module: &mut dyn Module,
alloc_id: AllocId,
mutability: rustc_hir::Mutability,
) -> DataId {
cx.todo.push(TodoItem::Alloc(alloc_id));
*cx.anon_allocs.entry(alloc_id).or_insert_with(|| {
module.declare_anonymous_data(mutability == rustc_hir::Mutability::Mut, false).unwrap()
})
}
fn data_id_for_static(
tcx: TyCtxt<'_>,
module: &mut dyn Module,
def_id: DefId,
definition: bool,
) -> DataId {
let rlinkage = tcx.codegen_fn_attrs(def_id).linkage;
let linkage = if definition {
crate::linkage::get_static_linkage(tcx, def_id)
} else if rlinkage == Some(rustc_middle::mir::mono::Linkage::ExternalWeak)
|| rlinkage == Some(rustc_middle::mir::mono::Linkage::WeakAny)
{
Linkage::Preemptible
} else {
Linkage::Import
};
let instance = Instance::mono(tcx, def_id).polymorphize(tcx);
let symbol_name = tcx.symbol_name(instance).name;
let ty = instance.ty(tcx, ParamEnv::reveal_all());
let is_mutable = if tcx.is_mutable_static(def_id) {
true
} else {
!ty.is_freeze(tcx.at(DUMMY_SP), ParamEnv::reveal_all())
};
let align = tcx.layout_of(ParamEnv::reveal_all().and(ty)).unwrap().align.pref.bytes();
let attrs = tcx.codegen_fn_attrs(def_id);
let data_id = module
.declare_data(
&*symbol_name,
linkage,
is_mutable,
attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL),
)
.unwrap();
if rlinkage.is_some() {
// Comment copied from https://github.com/rust-lang/rust/blob/45060c2a66dfd667f88bd8b94261b28a58d85bd5/src/librustc_codegen_llvm/consts.rs#L141
// Declare an internal global `extern_with_linkage_foo` which
// is initialized with the address of `foo`. If `foo` is
// discarded during linking (for example, if `foo` has weak
// linkage and there are no definitions), then
// `extern_with_linkage_foo` will instead be initialized to
// zero.
let ref_name = format!("_rust_extern_with_linkage_{}", symbol_name);
let ref_data_id = module.declare_data(&ref_name, Linkage::Local, false, false).unwrap();
let mut data_ctx = DataContext::new();
data_ctx.set_align(align);
let data = module.declare_data_in_data(data_id, &mut data_ctx);
data_ctx.define(std::iter::repeat(0).take(pointer_ty(tcx).bytes() as usize).collect());
data_ctx.write_data_addr(0, data, 0);
match module.define_data(ref_data_id, &data_ctx) {
// Every time the static is referenced there will be another definition of this global,
// so duplicate definitions are expected and allowed.
Err(ModuleError::DuplicateDefinition(_)) => {}
res => res.unwrap(),
}
ref_data_id
} else {
data_id
}
}
fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut ConstantCx) {
while let Some(todo_item) = cx.todo.pop() {
let (data_id, alloc, section_name) = match todo_item {
TodoItem::Alloc(alloc_id) => {
//println!("alloc_id {}", alloc_id);
let alloc = match tcx.get_global_alloc(alloc_id).unwrap() {
GlobalAlloc::Memory(alloc) => alloc,
GlobalAlloc::Function(_) | GlobalAlloc::Static(_) => unreachable!(),
};
let data_id = *cx.anon_allocs.entry(alloc_id).or_insert_with(|| {
module
.declare_anonymous_data(
alloc.mutability == rustc_hir::Mutability::Mut,
false,
)
.unwrap()
});
(data_id, alloc, None)
}
TodoItem::Static(def_id) => {
//println!("static {:?}", def_id);
let section_name = tcx.codegen_fn_attrs(def_id).link_section;
let alloc = tcx.eval_static_initializer(def_id).unwrap();
let data_id = data_id_for_static(tcx, module, def_id, true);
(data_id, alloc, section_name)
}
};
//("data_id {}", data_id);
if cx.done.contains(&data_id) {
continue;
}
let mut data_ctx = DataContext::new();
data_ctx.set_align(alloc.align.bytes());
if let Some(section_name) = section_name {
let (segment_name, section_name) = if tcx.sess.target.is_like_osx {
let section_name = section_name.as_str();
if let Some(names) = section_name.split_once(',') {
names
} else {
tcx.sess.fatal(&format!(
"#[link_section = \"{}\"] is not valid for macos target: must be segment and section separated by comma",
section_name
));
}
} else {
("", section_name.as_str())
};
data_ctx.set_segment_section(segment_name, section_name);
}
let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len()).to_vec();
data_ctx.define(bytes.into_boxed_slice());
for &(offset, alloc_id) in alloc.relocations().iter() {
let addend = {
let endianness = tcx.data_layout.endian;
let offset = offset.bytes() as usize;
let ptr_size = tcx.data_layout.pointer_size;
let bytes = &alloc.inspect_with_uninit_and_ptr_outside_interpreter(
offset..offset + ptr_size.bytes() as usize,
);
read_target_uint(endianness, bytes).unwrap()
};
let reloc_target_alloc = tcx.get_global_alloc(alloc_id).unwrap();
let data_id = match reloc_target_alloc {
GlobalAlloc::Function(instance) => {
assert_eq!(addend, 0);
let func_id = crate::abi::import_function(tcx, module, instance);
let local_func_id = module.declare_func_in_data(func_id, &mut data_ctx);
data_ctx.write_function_addr(offset.bytes() as u32, local_func_id);
continue;
}
GlobalAlloc::Memory(target_alloc) => {
data_id_for_alloc_id(cx, module, alloc_id, target_alloc.mutability)
}
GlobalAlloc::Static(def_id) => {
if tcx.codegen_fn_attrs(def_id).flags.contains(CodegenFnAttrFlags::THREAD_LOCAL)
{
tcx.sess.fatal(&format!(
"Allocation {:?} contains reference to TLS value {:?}",
alloc, def_id
));
}
// Don't push a `TodoItem::Static` here, as it will cause statics used by
// multiple crates to be duplicated between them. It isn't necessary anyway,
// as it will get pushed by `codegen_static` when necessary.
data_id_for_static(tcx, module, def_id, false)
}
};
let global_value = module.declare_data_in_data(data_id, &mut data_ctx);
data_ctx.write_data_addr(offset.bytes() as u32, global_value, addend as i64);
}
module.define_data(data_id, &data_ctx).unwrap();
cx.done.insert(data_id);
}
assert!(cx.todo.is_empty(), "{:?}", cx.todo);
}
pub(crate) fn mir_operand_get_const_val<'tcx>(
fx: &FunctionCx<'_, '_, 'tcx>,
operand: &Operand<'tcx>,
) -> Option<ConstValue<'tcx>> {
match operand {
Operand::Constant(const_) => match const_.literal {
ConstantKind::Ty(const_) => {
fx.monomorphize(const_).eval(fx.tcx, ParamEnv::reveal_all()).val.try_to_value()
}
ConstantKind::Val(val, _) => Some(val),
},
// FIXME(rust-lang/rust#85105): Casts like `IMM8 as u32` result in the const being stored
// inside a temporary before being passed to the intrinsic requiring the const argument.
// This code tries to find a single constant defining definition of the referenced local.
Operand::Copy(place) | Operand::Move(place) => {
if !place.projection.is_empty() {
return None;
}
let mut computed_const_val = None;
for bb_data in fx.mir.basic_blocks() {
for stmt in &bb_data.statements {
match &stmt.kind {
StatementKind::Assign(local_and_rvalue) if &local_and_rvalue.0 == place => {
match &local_and_rvalue.1 {
Rvalue::Cast(CastKind::Misc, operand, ty) => {
if computed_const_val.is_some() {
return None; // local assigned twice
}
if !matches!(ty.kind(), ty::Uint(_) | ty::Int(_)) {
return None;
}
let const_val = mir_operand_get_const_val(fx, operand)?;
if fx.layout_of(ty).size
!= const_val.try_to_scalar_int()?.size()
{
return None;
}
computed_const_val = Some(const_val);
}
Rvalue::Use(operand) => {
computed_const_val = mir_operand_get_const_val(fx, operand)
}
_ => return None,
}
}
StatementKind::SetDiscriminant { place: stmt_place, variant_index: _ }
if &**stmt_place == place =>
{
return None;
}
StatementKind::CopyNonOverlapping(_) => {
return None;
} // conservative handling
StatementKind::Assign(_)
| StatementKind::FakeRead(_)
| StatementKind::SetDiscriminant { .. }
| StatementKind::StorageLive(_)
| StatementKind::StorageDead(_)
| StatementKind::Retag(_, _)
| StatementKind::AscribeUserType(_, _)
| StatementKind::Coverage(_)
| StatementKind::Nop => {}
}
}
match &bb_data.terminator().kind {
TerminatorKind::Goto { .. }
| TerminatorKind::SwitchInt { .. }
| TerminatorKind::Resume
| TerminatorKind::Abort
| TerminatorKind::Return
| TerminatorKind::Unreachable
| TerminatorKind::Drop { .. }
| TerminatorKind::Assert { .. } => {}
TerminatorKind::DropAndReplace { .. }
| TerminatorKind::Yield { .. }
| TerminatorKind::GeneratorDrop
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. } => unreachable!(),
TerminatorKind::InlineAsm { .. } => return None,
TerminatorKind::Call { destination: Some((call_place, _)), .. }
if call_place == place =>
{
return None;
}
TerminatorKind::Call { .. } => {}
}
}
computed_const_val
}
}
}