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What if we discourage mir-inlining of box_new_uninit?

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This commit is contained in:
Scott McMurray
2026-02-17 00:31:19 -08:00
parent 1b767bf623
commit 4b03b97226
4 changed files with 35 additions and 156 deletions
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library/alloc/src/boxed.rs
+4
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@@ -238,6 +238,10 @@ pub struct Box<
/// Monomorphic function for allocating an uninit `Box`.
#[inline]
// The is a separate function to avoid doing it in every generic version, but it
// looks small to the mir inliner (particularly in panic=abort) so leave it to
// the backend to decide whether pulling it in everywhere is worth doing.
#[rustc_no_mir_inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
#[cfg(not(no_global_oom_handling))]
fn box_new_uninit(layout: Layout) -> *mut u8 {
tests/codegen-units/item-collection/opaque-return-impls.rs
+1
View File
@@ -45,6 +45,7 @@ pub fn foo2() -> Box<dyn TestTrait2> {
//~ MONO_ITEM fn foo2
//~ MONO_ITEM fn std::alloc::Global::alloc_impl_runtime
//~ MONO_ITEM fn std::boxed::Box::<TestStruct2>::new
//~ MONO_ITEM fn std::boxed::box_new_uninit
//~ MONO_ITEM fn std::ptr::NonNull::<T>::new_unchecked::precondition_check
struct Counter {
tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.32bit.panic-abort.diff
+15 -78
View File
@@ -11,8 +11,7 @@
let mut _9: *const [()];
let mut _10: std::boxed::Box<()>;
let mut _11: *const ();
let mut _14: std::alloc::Layout;
let mut _20: usize;
let mut _14: usize;
scope 1 {
debug vp_ctx => _1;
let _5: *const ();
@@ -25,12 +24,12 @@
scope 4 {
debug _x => _8;
}
scope 18 (inlined foo) {
let mut _21: *const [()];
scope 9 (inlined foo) {
let mut _15: *const [()];
}
}
scope 16 (inlined slice_from_raw_parts::<()>) {
scope 17 (inlined std::ptr::from_raw_parts::<[()], ()>) {
scope 7 (inlined slice_from_raw_parts::<()>) {
scope 8 (inlined std::ptr::from_raw_parts::<[()], ()>) {
}
}
}
@@ -40,29 +39,6 @@
let mut _13: *mut u8;
scope 6 {
}
scope 7 (inlined boxed::box_new_uninit) {
let mut _15: std::result::Result<std::ptr::NonNull<[u8]>, std::alloc::AllocError>;
let mut _16: isize;
let _17: std::ptr::NonNull<[u8]>;
let mut _18: !;
scope 8 {
scope 11 (inlined NonNull::<[u8]>::as_mut_ptr) {
scope 12 (inlined NonNull::<[u8]>::as_non_null_ptr) {
scope 13 (inlined NonNull::<[u8]>::cast::<u8>) {
let mut _19: *mut [u8];
scope 14 (inlined NonNull::<[u8]>::as_ptr) {
}
}
}
scope 15 (inlined NonNull::<u8>::as_ptr) {
}
}
}
scope 9 (inlined <std::alloc::Global as Allocator>::allocate) {
scope 10 (inlined std::alloc::Global::alloc_impl) {
}
}
}
}
bb0: {
@@ -74,15 +50,7 @@
+ _4 = const ();
StorageLive(_12);
StorageLive(_13);
StorageLive(_14);
- _14 = const <() as std::mem::SizedTypeProperties>::LAYOUT;
+ _14 = const Layout {{ size: 0_usize, align: std::ptr::Alignment {{ _inner_repr_trick: std::ptr::alignment::AlignmentEnum::_Align1Shl0 }} }};
StorageLive(_16);
StorageLive(_17);
StorageLive(_18);
StorageLive(_15);
- _15 = std::alloc::Global::alloc_impl_runtime(copy _14, const false) -> [return: bb5, unwind unreachable];
+ _15 = std::alloc::Global::alloc_impl_runtime(const Layout {{ size: 0_usize, align: std::ptr::Alignment {{ _inner_repr_trick: std::ptr::alignment::AlignmentEnum::_Align1Shl0 }} }}, const false) -> [return: bb5, unwind unreachable];
_13 = boxed::box_new_uninit(const <() as std::mem::SizedTypeProperties>::LAYOUT) -> [return: bb2, unwind unreachable];
}
bb1: {
@@ -92,30 +60,8 @@
}
bb2: {
unreachable;
}
bb3: {
- _18 = handle_alloc_error(move _14) -> unwind unreachable;
+ _18 = handle_alloc_error(const Layout {{ size: 0_usize, align: std::ptr::Alignment {{ _inner_repr_trick: std::ptr::alignment::AlignmentEnum::_Align1Shl0 }} }}) -> unwind unreachable;
}
bb4: {
_17 = copy ((_15 as Ok).0: std::ptr::NonNull<[u8]>);
- StorageLive(_19);
+ nop;
_19 = copy _17 as *mut [u8] (Transmute);
_13 = copy _19 as *mut u8 (PtrToPtr);
- StorageDead(_19);
+ nop;
StorageDead(_15);
StorageDead(_18);
StorageDead(_17);
StorageDead(_16);
StorageDead(_14);
- _12 = copy _13 as *mut () (PtrToPtr);
_12 = copy _13 as *mut () (PtrToPtr);
- (*_12) = move _4;
+ _12 = copy _19 as *mut () (PtrToPtr);
+ (*_12) = const ();
_3 = copy _13 as std::boxed::Box<()> (Transmute);
StorageDead(_13);
@@ -133,21 +79,21 @@
+ nop;
StorageLive(_7);
_7 = copy _5;
StorageLive(_20);
_20 = const 1_usize;
- _6 = *const [()] from (copy _7, copy _20);
StorageLive(_14);
_14 = const 1_usize;
- _6 = *const [()] from (copy _7, copy _14);
+ _6 = *const [()] from (copy _5, const 1_usize);
StorageDead(_20);
StorageDead(_14);
StorageDead(_7);
StorageLive(_8);
StorageLive(_9);
_9 = copy _6;
StorageLive(_21);
- _21 = copy _9;
StorageLive(_15);
- _15 = copy _9;
- _8 = copy _9 as *mut () (PtrToPtr);
+ _21 = copy _6;
+ _15 = copy _6;
+ _8 = copy _5 as *mut () (PtrToPtr);
StorageDead(_21);
StorageDead(_15);
StorageDead(_9);
_0 = const ();
StorageDead(_8);
@@ -157,14 +103,5 @@
+ nop;
drop(_3) -> [return: bb1, unwind unreachable];
}
bb5: {
_16 = discriminant(_15);
switchInt(move _16) -> [0: bb4, 1: bb3, otherwise: bb2];
}
+ }
+
+ ALLOC0 (size: 8, align: 4) {
+ 01 00 00 00 00 00 00 00 │ ........
}
tests/mir-opt/dont_reset_cast_kind_without_updating_operand.test.GVN.64bit.panic-abort.diff
+15 -78
View File
@@ -11,8 +11,7 @@
let mut _9: *const [()];
let mut _10: std::boxed::Box<()>;
let mut _11: *const ();
let mut _14: std::alloc::Layout;
let mut _20: usize;
let mut _14: usize;
scope 1 {
debug vp_ctx => _1;
let _5: *const ();
@@ -25,12 +24,12 @@
scope 4 {
debug _x => _8;
}
scope 18 (inlined foo) {
let mut _21: *const [()];
scope 9 (inlined foo) {
let mut _15: *const [()];
}
}
scope 16 (inlined slice_from_raw_parts::<()>) {
scope 17 (inlined std::ptr::from_raw_parts::<[()], ()>) {
scope 7 (inlined slice_from_raw_parts::<()>) {
scope 8 (inlined std::ptr::from_raw_parts::<[()], ()>) {
}
}
}
@@ -40,29 +39,6 @@
let mut _13: *mut u8;
scope 6 {
}
scope 7 (inlined boxed::box_new_uninit) {
let mut _15: std::result::Result<std::ptr::NonNull<[u8]>, std::alloc::AllocError>;
let mut _16: isize;
let _17: std::ptr::NonNull<[u8]>;
let mut _18: !;
scope 8 {
scope 11 (inlined NonNull::<[u8]>::as_mut_ptr) {
scope 12 (inlined NonNull::<[u8]>::as_non_null_ptr) {
scope 13 (inlined NonNull::<[u8]>::cast::<u8>) {
let mut _19: *mut [u8];
scope 14 (inlined NonNull::<[u8]>::as_ptr) {
}
}
}
scope 15 (inlined NonNull::<u8>::as_ptr) {
}
}
}
scope 9 (inlined <std::alloc::Global as Allocator>::allocate) {
scope 10 (inlined std::alloc::Global::alloc_impl) {
}
}
}
}
bb0: {
@@ -74,15 +50,7 @@
+ _4 = const ();
StorageLive(_12);
StorageLive(_13);
StorageLive(_14);
- _14 = const <() as std::mem::SizedTypeProperties>::LAYOUT;
+ _14 = const Layout {{ size: 0_usize, align: std::ptr::Alignment {{ _inner_repr_trick: std::ptr::alignment::AlignmentEnum::_Align1Shl0 }} }};
StorageLive(_16);
StorageLive(_17);
StorageLive(_18);
StorageLive(_15);
- _15 = std::alloc::Global::alloc_impl_runtime(copy _14, const false) -> [return: bb5, unwind unreachable];
+ _15 = std::alloc::Global::alloc_impl_runtime(const Layout {{ size: 0_usize, align: std::ptr::Alignment {{ _inner_repr_trick: std::ptr::alignment::AlignmentEnum::_Align1Shl0 }} }}, const false) -> [return: bb5, unwind unreachable];
_13 = boxed::box_new_uninit(const <() as std::mem::SizedTypeProperties>::LAYOUT) -> [return: bb2, unwind unreachable];
}
bb1: {
@@ -92,30 +60,8 @@
}
bb2: {
unreachable;
}
bb3: {
- _18 = handle_alloc_error(move _14) -> unwind unreachable;
+ _18 = handle_alloc_error(const Layout {{ size: 0_usize, align: std::ptr::Alignment {{ _inner_repr_trick: std::ptr::alignment::AlignmentEnum::_Align1Shl0 }} }}) -> unwind unreachable;
}
bb4: {
_17 = copy ((_15 as Ok).0: std::ptr::NonNull<[u8]>);
- StorageLive(_19);
+ nop;
_19 = copy _17 as *mut [u8] (Transmute);
_13 = copy _19 as *mut u8 (PtrToPtr);
- StorageDead(_19);
+ nop;
StorageDead(_15);
StorageDead(_18);
StorageDead(_17);
StorageDead(_16);
StorageDead(_14);
- _12 = copy _13 as *mut () (PtrToPtr);
_12 = copy _13 as *mut () (PtrToPtr);
- (*_12) = move _4;
+ _12 = copy _19 as *mut () (PtrToPtr);
+ (*_12) = const ();
_3 = copy _13 as std::boxed::Box<()> (Transmute);
StorageDead(_13);
@@ -133,21 +79,21 @@
+ nop;
StorageLive(_7);
_7 = copy _5;
StorageLive(_20);
_20 = const 1_usize;
- _6 = *const [()] from (copy _7, copy _20);
StorageLive(_14);
_14 = const 1_usize;
- _6 = *const [()] from (copy _7, copy _14);
+ _6 = *const [()] from (copy _5, const 1_usize);
StorageDead(_20);
StorageDead(_14);
StorageDead(_7);
StorageLive(_8);
StorageLive(_9);
_9 = copy _6;
StorageLive(_21);
- _21 = copy _9;
StorageLive(_15);
- _15 = copy _9;
- _8 = copy _9 as *mut () (PtrToPtr);
+ _21 = copy _6;
+ _15 = copy _6;
+ _8 = copy _5 as *mut () (PtrToPtr);
StorageDead(_21);
StorageDead(_15);
StorageDead(_9);
_0 = const ();
StorageDead(_8);
@@ -157,14 +103,5 @@
+ nop;
drop(_3) -> [return: bb1, unwind unreachable];
}
bb5: {
_16 = discriminant(_15);
switchInt(move _16) -> [0: bb4, 1: bb3, otherwise: bb2];
}
+ }
+
+ ALLOC0 (size: 16, align: 8) {
+ 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
}