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Auto merge of #123781 - RalfJung:miri-fn-identity, r=oli-obk

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Miri function identity hack: account for possible inlining

Having a non-lifetime generic is not the only reason a function can be duplicated. Another possibility is that the function may be eligible for cross-crate inlining. So also take into account the inlining attribute in this Miri hack for function pointer identity.

That said, `cross_crate_inlinable` will still sometimes return true even for `inline(never)` functions:
- when they are `DefKind::Ctor(..) | DefKind::Closure` -- I assume those cannot be `InlineAttr::Never` anyway?
- when `cross_crate_inline_threshold == InliningThreshold::Always`

so maybe this is still not quite the right criterion to use for function pointer identity.
This commit is contained in:
bors 2024-07-04 23:45:56 +00:00
commit 489233170a
14 changed files with 80 additions and 47 deletions
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8
compiler/rustc_codegen_cranelift/src/constant.rs
View File

@ -155,7 +155,7 @@ pub(crate) fn codegen_const_value<'tcx>(
fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
}
}
GlobalAlloc::Function(instance) => {
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);
@ -351,7 +351,9 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut Constant
TodoItem::Alloc(alloc_id) => {
let alloc = match tcx.global_alloc(alloc_id) {
GlobalAlloc::Memory(alloc) => alloc,
GlobalAlloc::Function(_) | GlobalAlloc::Static(_) | GlobalAlloc::VTable(..) => {
GlobalAlloc::Function { .. }
| GlobalAlloc::Static(_)
| GlobalAlloc::VTable(..) => {
unreachable!()
}
};
@ -415,7 +417,7 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut Constant
let reloc_target_alloc = tcx.global_alloc(alloc_id);
let data_id = match reloc_target_alloc {
GlobalAlloc::Function(instance) => {
GlobalAlloc::Function { instance, .. } => {
assert_eq!(addend, 0);
let func_id =
crate::abi::import_function(tcx, module, instance.polymorphize(tcx));

2
compiler/rustc_codegen_gcc/src/common.rs
View File

@ -220,7 +220,7 @@ fn scalar_to_backend(&self, cv: Scalar, layout: abi::Scalar, ty: Type<'gcc>) ->
}
value
}
GlobalAlloc::Function(fn_instance) => self.get_fn_addr(fn_instance),
GlobalAlloc::Function { instance, .. } => self.get_fn_addr(instance),
GlobalAlloc::VTable(ty, trait_ref) => {
let alloc = self
.tcx

4
compiler/rustc_codegen_llvm/src/common.rs
View File

@ -289,8 +289,8 @@ fn scalar_to_backend(&self, cv: Scalar, layout: abi::Scalar, llty: &'ll Type) ->
(value, AddressSpace::DATA)
}
}
GlobalAlloc::Function(fn_instance) => (
self.get_fn_addr(fn_instance.polymorphize(self.tcx)),
GlobalAlloc::Function { instance, .. } => (
self.get_fn_addr(instance.polymorphize(self.tcx)),
self.data_layout().instruction_address_space,
),
GlobalAlloc::VTable(ty, trait_ref) => {

14
compiler/rustc_const_eval/src/interpret/memory.rs
View File

@ -308,7 +308,7 @@ pub fn deallocate_ptr(
let Some((alloc_kind, mut alloc)) = self.memory.alloc_map.remove(&alloc_id) else {
// Deallocating global memory -- always an error
return Err(match self.tcx.try_get_global_alloc(alloc_id) {
Some(GlobalAlloc::Function(..)) => {
Some(GlobalAlloc::Function { .. }) => {
err_ub_custom!(
fluent::const_eval_invalid_dealloc,
alloc_id = alloc_id,
@ -555,7 +555,7 @@ fn get_global_alloc(
// Memory of a constant or promoted or anonymous memory referenced by a static.
(mem, None)
}
Some(GlobalAlloc::Function(..)) => throw_ub!(DerefFunctionPointer(id)),
Some(GlobalAlloc::Function { .. }) => throw_ub!(DerefFunctionPointer(id)),
Some(GlobalAlloc::VTable(..)) => throw_ub!(DerefVTablePointer(id)),
None => throw_ub!(PointerUseAfterFree(id, CheckInAllocMsg::MemoryAccessTest)),
Some(GlobalAlloc::Static(def_id)) => {
@ -828,7 +828,9 @@ pub fn get_alloc_info(&self, id: AllocId) -> (Size, Align, AllocKind) {
let alloc = alloc.inner();
(alloc.size(), alloc.align, AllocKind::LiveData)
}
Some(GlobalAlloc::Function(_)) => bug!("We already checked function pointers above"),
Some(GlobalAlloc::Function { .. }) => {
bug!("We already checked function pointers above")
}
Some(GlobalAlloc::VTable(..)) => {
// No data to be accessed here. But vtables are pointer-aligned.
return (Size::ZERO, self.tcx.data_layout.pointer_align.abi, AllocKind::VTable);
@ -865,7 +867,7 @@ fn get_fn_alloc(&self, id: AllocId) -> Option<FnVal<'tcx, M::ExtraFnVal>> {
Some(FnVal::Other(*extra))
} else {
match self.tcx.try_get_global_alloc(id) {
Some(GlobalAlloc::Function(instance)) => Some(FnVal::Instance(instance)),
Some(GlobalAlloc::Function { instance, .. }) => Some(FnVal::Instance(instance)),
_ => None,
}
}
@ -1056,8 +1058,8 @@ fn write_allocation_track_relocs<'tcx, Prov: Provenance, Extra, Bytes: AllocByte
alloc.inner(),
)?;
}
Some(GlobalAlloc::Function(func)) => {
write!(fmt, " (fn: {func})")?;
Some(GlobalAlloc::Function { instance, .. }) => {
write!(fmt, " (fn: {instance})")?;
}
Some(GlobalAlloc::VTable(ty, Some(trait_ref))) => {
write!(fmt, " (vtable: impl {trait_ref} for {ty})")?;

2
compiler/rustc_const_eval/src/interpret/validity.rs
View File

@ -745,7 +745,7 @@ fn mutability<'tcx>(ecx: &InterpCx<'tcx, impl Machine<'tcx>>, alloc_id: AllocId)
}
}
GlobalAlloc::Memory(alloc) => alloc.inner().mutability,
GlobalAlloc::Function(..) | GlobalAlloc::VTable(..) => {
GlobalAlloc::Function { .. } | GlobalAlloc::VTable(..) => {
// These are immutable, we better don't allow mutable pointers here.
Mutability::Not
}

73
compiler/rustc_middle/src/mir/interpret/mod.rs
View File

@ -18,6 +18,7 @@
use tracing::{debug, trace};
use rustc_ast::LitKind;
use rustc_attr::InlineAttr;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync::{HashMapExt, Lock};
use rustc_errors::ErrorGuaranteed;
@ -134,10 +135,11 @@ pub fn specialized_encode_alloc_id<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>>(
AllocDiscriminant::Alloc.encode(encoder);
alloc.encode(encoder);
}
GlobalAlloc::Function(fn_instance) => {
trace!("encoding {:?} with {:#?}", alloc_id, fn_instance);
GlobalAlloc::Function { instance, unique } => {
trace!("encoding {:?} with {:#?}", alloc_id, instance);
AllocDiscriminant::Fn.encode(encoder);
fn_instance.encode(encoder);
instance.encode(encoder);
unique.encode(encoder);
}
GlobalAlloc::VTable(ty, poly_trait_ref) => {
trace!("encoding {:?} with {ty:#?}, {poly_trait_ref:#?}", alloc_id);
@ -285,7 +287,12 @@ pub fn decode_alloc_id<'tcx, D>(&self, decoder: &mut D) -> AllocId
trace!("creating fn alloc ID");
let instance = ty::Instance::decode(decoder);
trace!("decoded fn alloc instance: {:?}", instance);
let alloc_id = decoder.interner().reserve_and_set_fn_alloc(instance);
let unique = bool::decode(decoder);
// Here we cannot call `reserve_and_set_fn_alloc` as that would use a query, which
// is not possible in this context. That's why the allocation stores
// whether it is unique or not.
let alloc_id =
decoder.interner().reserve_and_set_fn_alloc_internal(instance, unique);
alloc_id
}
AllocDiscriminant::VTable => {
@ -323,7 +330,12 @@ pub fn decode_alloc_id<'tcx, D>(&self, decoder: &mut D) -> AllocId
#[derive(Debug, Clone, Eq, PartialEq, Hash, TyDecodable, TyEncodable, HashStable)]
pub enum GlobalAlloc<'tcx> {
/// The alloc ID is used as a function pointer.
Function(Instance<'tcx>),
Function {
instance: Instance<'tcx>,
/// Stores whether this instance is unique, i.e. all pointers to this function use the same
/// alloc ID.
unique: bool,
},
/// This alloc ID points to a symbolic (not-reified) vtable.
VTable(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>),
/// The alloc ID points to a "lazy" static variable that did not get computed (yet).
@ -349,7 +361,7 @@ pub fn unwrap_memory(&self) -> ConstAllocation<'tcx> {
#[inline]
pub fn unwrap_fn(&self) -> Instance<'tcx> {
match *self {
GlobalAlloc::Function(instance) => instance,
GlobalAlloc::Function { instance, .. } => instance,
_ => bug!("expected function, got {:?}", self),
}
}
@ -368,7 +380,7 @@ pub fn unwrap_vtable(&self) -> (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tc
#[inline]
pub fn address_space(&self, cx: &impl HasDataLayout) -> AddressSpace {
match self {
GlobalAlloc::Function(..) => cx.data_layout().instruction_address_space,
GlobalAlloc::Function { .. } => cx.data_layout().instruction_address_space,
GlobalAlloc::Static(..) | GlobalAlloc::Memory(..) | GlobalAlloc::VTable(..) => {
AddressSpace::DATA
}
@ -426,7 +438,7 @@ pub fn reserve_alloc_id(self) -> AllocId {
fn reserve_and_set_dedup(self, alloc: GlobalAlloc<'tcx>) -> AllocId {
let mut alloc_map = self.alloc_map.lock();
match alloc {
GlobalAlloc::Function(..) | GlobalAlloc::Static(..) | GlobalAlloc::VTable(..) => {}
GlobalAlloc::Function { .. } | GlobalAlloc::Static(..) | GlobalAlloc::VTable(..) => {}
GlobalAlloc::Memory(..) => bug!("Trying to dedup-reserve memory with real data!"),
}
if let Some(&alloc_id) = alloc_map.dedup.get(&alloc) {
@ -445,30 +457,45 @@ pub fn reserve_and_set_static_alloc(self, static_id: DefId) -> AllocId {
self.reserve_and_set_dedup(GlobalAlloc::Static(static_id))
}
/// Generates an `AllocId` for a function. The caller must already have decided whether this
/// function obtains a unique AllocId or gets de-duplicated via the cache.
fn reserve_and_set_fn_alloc_internal(self, instance: Instance<'tcx>, unique: bool) -> AllocId {
let alloc = GlobalAlloc::Function { instance, unique };
if unique {
// Deduplicate.
self.reserve_and_set_dedup(alloc)
} else {
// Get a fresh ID.
let mut alloc_map = self.alloc_map.lock();
let id = alloc_map.reserve();
alloc_map.alloc_map.insert(id, alloc);
id
}
}
/// Generates an `AllocId` for a function. Depending on the function type,
/// this might get deduplicated or assigned a new ID each time.
pub fn reserve_and_set_fn_alloc(self, instance: Instance<'tcx>) -> AllocId {
// Functions cannot be identified by pointers, as asm-equal functions can get deduplicated
// by the linker (we set the "unnamed_addr" attribute for LLVM) and functions can be
// duplicated across crates.
// We thus generate a new `AllocId` for every mention of a function. This means that
// `main as fn() == main as fn()` is false, while `let x = main as fn(); x == x` is true.
// However, formatting code relies on function identity (see #58320), so we only do
// this for generic functions. Lifetime parameters are ignored.
// duplicated across crates. We thus generate a new `AllocId` for every mention of a
// function. This means that `main as fn() == main as fn()` is false, while `let x = main as
// fn(); x == x` is true. However, as a quality-of-life feature it can be useful to identify
// certain functions uniquely, e.g. for backtraces. So we identify whether codegen will
// actually emit duplicate functions. It does that when they have non-lifetime generics, or
// when they can be inlined. All other functions are given a unique address.
// This is not a stable guarantee! The `inline` attribute is a hint and cannot be relied
// upon for anything. But if we don't do this, backtraces look terrible.
let is_generic = instance
.args
.into_iter()
.any(|kind| !matches!(kind.unpack(), GenericArgKind::Lifetime(_)));
if is_generic {
// Get a fresh ID.
let mut alloc_map = self.alloc_map.lock();
let id = alloc_map.reserve();
alloc_map.alloc_map.insert(id, GlobalAlloc::Function(instance));
id
} else {
// Deduplicate.
self.reserve_and_set_dedup(GlobalAlloc::Function(instance))
}
let can_be_inlined = match self.codegen_fn_attrs(instance.def_id()).inline {
InlineAttr::Never => false,
_ => true,
};
let unique = !is_generic && !can_be_inlined;
self.reserve_and_set_fn_alloc_internal(instance, unique)
}
/// Generates an `AllocId` for a (symbolic, not-reified) vtable. Will get deduplicated.

2
compiler/rustc_middle/src/mir/pretty.rs
View File

@ -1449,7 +1449,7 @@ fn visit_const_operand(&mut self, c: &ConstOperand<'tcx>, _: Location) {
// This can't really happen unless there are bugs, but it doesn't cost us anything to
// gracefully handle it and allow buggy rustc to be debugged via allocation printing.
None => write!(w, " (deallocated)")?,
Some(GlobalAlloc::Function(inst)) => write!(w, " (fn: {inst})")?,
Some(GlobalAlloc::Function { instance, .. }) => write!(w, " (fn: {instance})")?,
Some(GlobalAlloc::VTable(ty, Some(trait_ref))) => {
write!(w, " (vtable: impl {trait_ref} for {ty})")?
}

4
compiler/rustc_middle/src/ty/print/pretty.rs
View File

@ -1667,7 +1667,7 @@ fn pretty_print_const_scalar_ptr(
Some(GlobalAlloc::Static(def_id)) => {
p!(write("<static({:?})>", def_id))
}
Some(GlobalAlloc::Function(_)) => p!("<function>"),
Some(GlobalAlloc::Function { .. }) => p!("<function>"),
Some(GlobalAlloc::VTable(..)) => p!("<vtable>"),
None => p!("<dangling pointer>"),
}
@ -1679,7 +1679,7 @@ fn pretty_print_const_scalar_ptr(
ty::FnPtr(_) => {
// FIXME: We should probably have a helper method to share code with the "Byte strings"
// printing above (which also has to handle pointers to all sorts of things).
if let Some(GlobalAlloc::Function(instance)) =
if let Some(GlobalAlloc::Function { instance, .. }) =
self.tcx().try_get_global_alloc(prov.alloc_id())
{
self.typed_value(

8
compiler/rustc_monomorphize/src/collector.rs
View File

@ -1160,10 +1160,10 @@ fn collect_alloc<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut MonoIt
});
}
}
GlobalAlloc::Function(fn_instance) => {
if should_codegen_locally(tcx, fn_instance) {
trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
output.push(create_fn_mono_item(tcx, fn_instance, DUMMY_SP));
GlobalAlloc::Function { instance, .. } => {
if should_codegen_locally(tcx, instance) {
trace!("collecting {:?} with {:#?}", alloc_id, instance);
output.push(create_fn_mono_item(tcx, instance, DUMMY_SP));
}
}
GlobalAlloc::VTable(ty, trait_ref) => {

2
compiler/rustc_passes/src/reachable.rs
View File

@ -310,7 +310,7 @@ fn propagate_from_alloc(&mut self, alloc: ConstAllocation<'tcx>) {
GlobalAlloc::Static(def_id) => {
self.propagate_item(Res::Def(self.tcx.def_kind(def_id), def_id))
}
GlobalAlloc::Function(instance) => {
GlobalAlloc::Function { instance, .. } => {
// Manually visit to actually see the instance's `DefId`. Type visitors won't see it
self.propagate_item(Res::Def(
self.tcx.def_kind(instance.def_id()),

2
compiler/rustc_smir/src/rustc_smir/convert/mir.rs
View File

@ -709,7 +709,7 @@ impl<'tcx> Stable<'tcx> for mir::interpret::GlobalAlloc<'tcx> {
fn stable(&self, tables: &mut Tables<'_>) -> Self::T {
match self {
mir::interpret::GlobalAlloc::Function(instance) => {
mir::interpret::GlobalAlloc::Function { instance, .. } => {
GlobalAlloc::Function(instance.stable(tables))
}
mir::interpret::GlobalAlloc::VTable(ty, trait_ref) => {

2
src/tools/miri/src/shims/backtrace.rs
View File

@ -119,7 +119,7 @@ fn resolve_frame_pointer(
let (alloc_id, offset, _prov) = this.ptr_get_alloc_id(ptr)?;
// This has to be an actual global fn ptr, not a dlsym function.
let fn_instance = if let Some(GlobalAlloc::Function(instance)) =
let fn_instance = if let Some(GlobalAlloc::Function { instance, .. }) =
this.tcx.try_get_global_alloc(alloc_id)
{
instance

3
src/tools/miri/tests/pass/function_pointers.rs
View File

@ -23,6 +23,7 @@ fn h(i: i32, j: i32) -> i32 {
j * i * 7
}
#[inline(never)]
fn i() -> i32 {
73
}
@ -77,7 +78,7 @@ fn main() {
assert_eq!(indirect_mut3(h), 210);
assert_eq!(indirect_once3(h), 210);
// Check that `i` always has the same address. This is not guaranteed
// but Miri currently uses a fixed address for monomorphic functions.
// but Miri currently uses a fixed address for non-inlineable monomorphic functions.
assert!(return_fn_ptr(i) == i);
assert!(return_fn_ptr(i) as unsafe fn() -> i32 == i as fn() -> i32 as unsafe fn() -> i32);
// Miri gives different addresses to different reifications of a generic function.

1
src/tools/miri/tests/pass/issues/issue-91636.rs
View File

@ -10,6 +10,7 @@ fn new(subr: BuiltIn) -> Self {
}
}
#[inline(never)]
fn dummy(_: &str) {}
fn main() {