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Rollup merge of rust-lang#59348 - matthewjasper:cleanup-drop-shims, r…
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…=arielb1

Clean up and add tests for slice drop shims

Adds a test for the MIR generated by `real_drop_in_place::<[T]>`. Also slightly reduces the number of statements and locals used in the shim.

r? @RalfJung
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@Centril
Centril committed May 9, 2019
2 parents a784a80 + 6fff547 commit 62ab971
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Showing 2 changed files with 153 additions and 57 deletions.
122 changes: 65 additions & 57 deletions src/librustc_mir/util/elaborate_drops.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ use rustc::ty::util::IntTypeExt;
use rustc_data_structures::indexed_vec::Idx;
use crate::util::patch::MirPatch;

use std::u32;
use std::convert::TryInto;

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum DropFlagState {
Expand Down Expand Up @@ -545,10 +545,9 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
self.elaborator.patch().new_block(result)
}

/// create a loop that drops an array:
///

/// Create a loop that drops an array:
///
/// ```text
/// loop-block:
/// can_go = cur == length_or_end
/// if can_go then succ else drop-block
Expand All @@ -561,15 +560,16 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
/// cur = cur + 1
/// }
/// drop(ptr)
fn drop_loop(&mut self,
succ: BasicBlock,
cur: Local,
length_or_end: &Place<'tcx>,
ety: Ty<'tcx>,
unwind: Unwind,
ptr_based: bool)
-> BasicBlock
{
/// ```
fn drop_loop(
&mut self,
succ: BasicBlock,
cur: Local,
length_or_end: &Place<'tcx>,
ety: Ty<'tcx>,
unwind: Unwind,
ptr_based: bool,
) -> BasicBlock {
let copy = |place: &Place<'tcx>| Operand::Copy(place.clone());
let move_ = |place: &Place<'tcx>| Operand::Move(place.clone());
let tcx = self.tcx();
Expand All @@ -591,13 +591,13 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
elem: ProjectionElem::Deref,
}))
),
Rvalue::BinaryOp(BinOp::Offset, copy(&Place::Base(PlaceBase::Local(cur))), one))
Rvalue::BinaryOp(BinOp::Offset, move_(&Place::Base(PlaceBase::Local(cur))), one))
} else {
(Rvalue::Ref(
tcx.lifetimes.re_erased,
BorrowKind::Mut { allow_two_phase_borrow: false },
self.place.clone().index(cur)),
Rvalue::BinaryOp(BinOp::Add, copy(&Place::Base(PlaceBase::Local(cur))), one))
Rvalue::BinaryOp(BinOp::Add, move_(&Place::Base(PlaceBase::Local(cur))), one))
};

let drop_block = BasicBlockData {
Expand Down Expand Up @@ -647,9 +647,9 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
// }

if let Some(size) = opt_size {
assert!(size <= (u32::MAX as u64),
"move out check doesn't implemented for array bigger then u32");
let size = size as u32;
let size: u32 = size.try_into().unwrap_or_else(|_| {
bug!("move out check isn't implemented for array sizes bigger than u32::MAX");
});
let fields: Vec<(Place<'tcx>, Option<D::Path>)> = (0..size).map(|i| {
(self.place.clone().elem(ProjectionElem::ConstantIndex{
offset: i,
Expand All @@ -667,33 +667,42 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>

let move_ = |place: &Place<'tcx>| Operand::Move(place.clone());
let tcx = self.tcx();
let size = &Place::Base(PlaceBase::Local(self.new_temp(tcx.types.usize)));
let size_is_zero = &Place::Base(PlaceBase::Local(self.new_temp(tcx.types.bool)));
let elem_size = &Place::Base(PlaceBase::Local(self.new_temp(tcx.types.usize)));
let len = &Place::Base(PlaceBase::Local(self.new_temp(tcx.types.usize)));

static USIZE_SWITCH_ZERO: &[u128] = &[0];

let base_block = BasicBlockData {
statements: vec![
self.assign(size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
self.assign(size_is_zero, Rvalue::BinaryOp(BinOp::Eq,
move_(size),
self.constant_usize(0)))
self.assign(elem_size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
self.assign(len, Rvalue::Len(self.place.clone())),
],
is_cleanup: self.unwind.is_cleanup(),
terminator: Some(Terminator {
source_info: self.source_info,
kind: TerminatorKind::if_(
tcx,
move_(size_is_zero),
self.drop_loop_pair(ety, false),
self.drop_loop_pair(ety, true)
)
kind: TerminatorKind::SwitchInt {
discr: move_(elem_size),
switch_ty: tcx.types.usize,
values: From::from(USIZE_SWITCH_ZERO),
targets: vec![
self.drop_loop_pair(ety, false, len.clone()),
self.drop_loop_pair(ety, true, len.clone()),
],
},
})
};
self.elaborator.patch().new_block(base_block)
}

// create a pair of drop-loops of `place`, which drops its contents
// even in the case of 1 panic. If `ptr_based`, create a pointer loop,
// otherwise create an index loop.
fn drop_loop_pair(&mut self, ety: Ty<'tcx>, ptr_based: bool) -> BasicBlock {
/// Ceates a pair of drop-loops of `place`, which drops its contents, even
/// in the case of 1 panic. If `ptr_based`, creates a pointer loop,
/// otherwise create an index loop.
fn drop_loop_pair(
&mut self,
ety: Ty<'tcx>,
ptr_based: bool,
length: Place<'tcx>,
) -> BasicBlock {
debug!("drop_loop_pair({:?}, {:?})", ety, ptr_based);
let tcx = self.tcx();
let iter_ty = if ptr_based {
Expand All @@ -703,7 +712,6 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
};

let cur = self.new_temp(iter_ty);
let length = Place::Base(PlaceBase::Local(self.new_temp(tcx.types.usize)));
let length_or_end = if ptr_based {
// FIXME check if we want to make it return a `Place` directly
// if all use sites want a `Place::Base` anyway.
Expand All @@ -722,41 +730,41 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
ptr_based)
});

let succ = self.succ; // FIXME(#43234)
let loop_block = self.drop_loop(
succ,
self.succ,
cur,
&length_or_end,
ety,
unwind,
ptr_based);

let cur = Place::Base(PlaceBase::Local(cur));
let zero = self.constant_usize(0);
let mut drop_block_stmts = vec![];
drop_block_stmts.push(self.assign(&length, Rvalue::Len(self.place.clone())));
if ptr_based {
let drop_block_stmts = if ptr_based {
let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
let tmp = Place::Base(PlaceBase::Local(self.new_temp(tmp_ty)));
// tmp = &mut P;
// cur = tmp as *mut T;
// end = Offset(cur, len);
drop_block_stmts.push(self.assign(&tmp, Rvalue::Ref(
tcx.lifetimes.re_erased,
BorrowKind::Mut { allow_two_phase_borrow: false },
self.place.clone()
)));
drop_block_stmts.push(self.assign(&cur, Rvalue::Cast(
CastKind::Misc, Operand::Move(tmp), iter_ty
)));
drop_block_stmts.push(self.assign(&length_or_end,
Rvalue::BinaryOp(BinOp::Offset,
Operand::Copy(cur), Operand::Move(length)
)));
vec![
self.assign(&tmp, Rvalue::Ref(
tcx.lifetimes.re_erased,
BorrowKind::Mut { allow_two_phase_borrow: false },
self.place.clone()
)),
self.assign(
&cur,
Rvalue::Cast(CastKind::Misc, Operand::Move(tmp), iter_ty),
),
self.assign(
&length_or_end,
Rvalue::BinaryOp(BinOp::Offset, Operand::Copy(cur), Operand::Move(length)
)),
]
} else {
// index = 0 (length already pushed)
drop_block_stmts.push(self.assign(&cur, Rvalue::Use(zero)));
}
// cur = 0 (length already pushed)
let zero = self.constant_usize(0);
vec![self.assign(&cur, Rvalue::Use(zero))]
};
let drop_block = self.elaborator.patch().new_block(BasicBlockData {
statements: drop_block_stmts,
is_cleanup: unwind.is_cleanup(),
Expand All @@ -768,7 +776,7 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>

// FIXME(#34708): handle partially-dropped array/slice elements.
let reset_block = self.drop_flag_reset_block(DropFlagMode::Deep, drop_block, unwind);
self.drop_flag_test_block(reset_block, succ, unwind)
self.drop_flag_test_block(reset_block, self.succ, unwind)
}

/// The slow-path - create an "open", elaborated drop for a type
Expand Down
88 changes: 88 additions & 0 deletions src/test/mir-opt/slice-drop-shim.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,88 @@
fn main() {
std::ptr::drop_in_place::<[String]> as unsafe fn(_);
}

// END RUST SOURCE

// START rustc.ptr-real_drop_in_place.[std__string__String].AddMovesForPackedDrops.before.mir
// let mut _2: usize;
// let mut _3: usize;
// let mut _4: usize;
// let mut _5: &mut std::string::String;
// let mut _6: bool;
// let mut _7: &mut std::string::String;
// let mut _8: bool;
// let mut _9: *mut std::string::String;
// let mut _10: *mut std::string::String;
// let mut _11: &mut std::string::String;
// let mut _12: bool;
// let mut _13: &mut std::string::String;
// let mut _14: bool;
// let mut _15: *mut [std::string::String];
// bb0: {
// goto -> bb15;
// }
// bb1: {
// return;
// }
// bb2 (cleanup): {
// resume;
// }
// bb3 (cleanup): {
// _5 = &mut (*_1)[_4];
// _4 = Add(move _4, const 1usize);
// drop((*_5)) -> bb4;
// }
// bb4 (cleanup): {
// _6 = Eq(_4, _3);
// switchInt(move _6) -> [false: bb3, otherwise: bb2];
// }
// bb5: {
// _7 = &mut (*_1)[_4];
// _4 = Add(move _4, const 1usize);
// drop((*_7)) -> [return: bb6, unwind: bb4];
// }
// bb6: {
// _8 = Eq(_4, _3);
// switchInt(move _8) -> [false: bb5, otherwise: bb1];
// }
// bb7: {
// _4 = const 0usize;
// goto -> bb6;
// }
// bb8: {
// goto -> bb7;
// }
// bb9 (cleanup): {
// _11 = &mut (*_9);
// _9 = Offset(move _9, const 1usize);
// drop((*_11)) -> bb10;
// }
// bb10 (cleanup): {
// _12 = Eq(_9, _10);
// switchInt(move _12) -> [false: bb9, otherwise: bb2];
// }
// bb11: {
// _13 = &mut (*_9);
// _9 = Offset(move _9, const 1usize);
// drop((*_13)) -> [return: bb12, unwind: bb10];
// }
// bb12: {
// _14 = Eq(_9, _10);
// switchInt(move _14) -> [false: bb11, otherwise: bb1];
// }
// bb13: {
// _15 = &mut (*_1);
// _9 = move _15 as *mut std::string::String (Misc);
// _10 = Offset(_9, move _3);
// goto -> bb12;
// }
// bb14: {
// goto -> bb13;
// }
// bb15: {
// _2 = SizeOf(std::string::String);
// _3 = Len((*_1));
// switchInt(move _2) -> [0usize: bb8, otherwise: bb14];
// }
// END rustc.ptr-real_drop_in_place.[std__string__String].AddMovesForPackedDrops.before.mir

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