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Use PtrMetadata instead of Len in slice drop shims

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This commit is contained in:
Scott McMurray 2024-12-14 21:20:15 -08:00
parent e1a727e466
commit 8acccdc355
3 changed files with 92 additions and 27 deletions
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75
compiler/rustc_mir_dataflow/src/elaborate_drops.rs
View file

@ -1,4 +1,4 @@
use std::{fmt, iter};
use std::{fmt, iter, mem};
use rustc_abi::{FIRST_VARIANT, FieldIdx, VariantIdx};
use rustc_hir::lang_items::LangItem;
@ -6,6 +6,7 @@ use rustc_index::Idx;
use rustc_middle::mir::patch::MirPatch;
use rustc_middle::mir::*;
use rustc_middle::span_bug;
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::util::IntTypeExt;
use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt};
use rustc_span::DUMMY_SP;
@ -738,8 +739,13 @@ where
loop_block
}
fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);
fn open_drop_for_array(
&mut self,
array_ty: Ty<'tcx>,
ety: Ty<'tcx>,
opt_size: Option<u64>,
) -> BasicBlock {
debug!("open_drop_for_array({:?}, {:?}, {:?})", array_ty, ety, opt_size);
let tcx = self.tcx();
if let Some(size) = opt_size {
@ -801,13 +807,50 @@ where
}
}
self.drop_loop_pair(ety)
let array_ptr_ty = Ty::new_mut_ptr(tcx, array_ty);
let array_ptr = self.new_temp(array_ptr_ty);
let slice_ty = Ty::new_slice(tcx, ety);
let slice_ptr_ty = Ty::new_mut_ptr(tcx, slice_ty);
let slice_ptr = self.new_temp(slice_ptr_ty);
let mut delegate_block = BasicBlockData {
statements: vec![
self.assign(Place::from(array_ptr), Rvalue::RawPtr(Mutability::Mut, self.place)),
self.assign(
Place::from(slice_ptr),
Rvalue::Cast(
CastKind::PointerCoercion(
PointerCoercion::Unsize,
CoercionSource::Implicit,
),
Operand::Move(Place::from(array_ptr)),
slice_ptr_ty,
),
),
],
is_cleanup: self.unwind.is_cleanup(),
terminator: None,
};
let array_place = mem::replace(
&mut self.place,
Place::from(slice_ptr).project_deeper(&[PlaceElem::Deref], tcx),
);
let slice_block = self.drop_loop_pair_for_slice(ety);
self.place = array_place;
delegate_block.terminator = Some(Terminator {
source_info: self.source_info,
kind: TerminatorKind::Goto { target: slice_block },
});
self.elaborator.patch().new_block(delegate_block)
}
/// Creates a pair of drop-loops of `place`, which drops its contents, even
/// in the case of 1 panic.
fn drop_loop_pair(&mut self, ety: Ty<'tcx>) -> BasicBlock {
debug!("drop_loop_pair({:?})", ety);
fn drop_loop_pair_for_slice(&mut self, ety: Ty<'tcx>) -> BasicBlock {
debug!("drop_loop_pair_for_slice({:?})", ety);
let tcx = self.tcx();
let len = self.new_temp(tcx.types.usize);
let cur = self.new_temp(tcx.types.usize);
@ -817,10 +860,24 @@ where
let loop_block = self.drop_loop(self.succ, cur, len, ety, unwind);
let [PlaceElem::Deref] = self.place.projection.as_slice() else {
span_bug!(
self.source_info.span,
"Expected place for slice drop shim to be *_n, but it's {:?}",
self.place,
);
};
let zero = self.constant_usize(0);
let block = BasicBlockData {
statements: vec![
self.assign(len.into(), Rvalue::Len(self.place)),
self.assign(
len.into(),
Rvalue::UnaryOp(
UnOp::PtrMetadata,
Operand::Copy(Place::from(self.place.local)),
),
),
self.assign(cur.into(), Rvalue::Use(zero)),
],
is_cleanup: unwind.is_cleanup(),
@ -863,9 +920,9 @@ where
ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind),
ty::Array(ety, size) => {
let size = size.try_to_target_usize(self.tcx());
self.open_drop_for_array(*ety, size)
self.open_drop_for_array(ty, *ety, size)
}
ty::Slice(ety) => self.drop_loop_pair(*ety),
ty::Slice(ety) => self.drop_loop_pair_for_slice(*ety),
_ => span_bug!(self.source_info.span, "open drop from non-ADT `{:?}`", ty),
}

42
tests/mir-opt/slice_drop_shim.core.ptr-drop_in_place.[String;42].AddMovesForPackedDrops.before.mir
View file

@ -2,15 +2,17 @@
fn std::ptr::drop_in_place(_1: *mut [String; 42]) -> () {
let mut _0: ();
let mut _2: usize;
let mut _3: usize;
let mut _4: *mut std::string::String;
let mut _5: bool;
let mut _2: *mut [std::string::String; 42];
let mut _3: *mut [std::string::String];
let mut _4: usize;
let mut _5: usize;
let mut _6: *mut std::string::String;
let mut _7: bool;
let mut _8: *mut std::string::String;
let mut _9: bool;
bb0: {
goto -> bb8;
goto -> bb9;
}
bb1: {
@ -22,34 +24,40 @@ fn std::ptr::drop_in_place(_1: *mut [String; 42]) -> () {
}
bb3 (cleanup): {
_4 = &raw mut (*_1)[_3];
_3 = Add(move _3, const 1_usize);
drop((*_4)) -> [return: bb4, unwind terminate(cleanup)];
_6 = &raw mut (*_3)[_5];
_5 = Add(move _5, const 1_usize);
drop((*_6)) -> [return: bb4, unwind terminate(cleanup)];
}
bb4 (cleanup): {
_5 = Eq(copy _3, copy _2);
switchInt(move _5) -> [0: bb3, otherwise: bb2];
_7 = Eq(copy _5, copy _4);
switchInt(move _7) -> [0: bb3, otherwise: bb2];
}
bb5: {
_6 = &raw mut (*_1)[_3];
_3 = Add(move _3, const 1_usize);
drop((*_6)) -> [return: bb6, unwind: bb4];
_8 = &raw mut (*_3)[_5];
_5 = Add(move _5, const 1_usize);
drop((*_8)) -> [return: bb6, unwind: bb4];
}
bb6: {
_7 = Eq(copy _3, copy _2);
switchInt(move _7) -> [0: bb5, otherwise: bb1];
_9 = Eq(copy _5, copy _4);
switchInt(move _9) -> [0: bb5, otherwise: bb1];
}
bb7: {
_2 = Len((*_1));
_3 = const 0_usize;
_4 = PtrMetadata(copy _3);
_5 = const 0_usize;
goto -> bb6;
}
bb8: {
goto -> bb7;
}
bb9: {
_2 = &raw mut (*_1);
_3 = move _2 as *mut [std::string::String] (PointerCoercion(Unsize, Implicit));
goto -> bb8;
}
}

2
tests/mir-opt/slice_drop_shim.core.ptr-drop_in_place.[String].AddMovesForPackedDrops.before.mir
View file

@ -44,7 +44,7 @@ fn std::ptr::drop_in_place(_1: *mut [String]) -> () {
}
bb7: {
_2 = Len((*_1));
_2 = PtrMetadata(copy _1);
_3 = const 0_usize;
goto -> bb6;
}