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Auto merge of #109085 - tmiasko:index-based, r=WaffleLapkin
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Use index based drop loop for slices and arrays

Instead of building two kinds of drop pair loops, of which only one will be eventually used at runtime in a given monomorphization, always use index based loop.
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@bors
bors committed Mar 17, 2023
2 parents 511364e + cf0e78b commit 2d64f22
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Showing 2 changed files with 49 additions and 164 deletions.
133 changes: 32 additions & 101 deletions compiler/rustc_mir_dataflow/src/elaborate_drops.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -655,26 +655,20 @@ where
///
/// ```text
/// loop-block:
/// can_go = cur == length_or_end
/// can_go = cur == len
/// if can_go then succ else drop-block
/// drop-block:
/// if ptr_based {
/// ptr = cur
/// cur = cur.offset(1)
/// } else {
/// ptr = &raw mut P[cur]
/// cur = cur + 1
/// }
/// ptr = &raw mut P[cur]
/// cur = cur + 1
/// drop(ptr)
/// ```
fn drop_loop(
&mut self,
succ: BasicBlock,
cur: Local,
length_or_end: Place<'tcx>,
len: Local,
ety: Ty<'tcx>,
unwind: Unwind,
ptr_based: bool,
) -> BasicBlock {
let copy = |place: Place<'tcx>| Operand::Copy(place);
let move_ = |place: Place<'tcx>| Operand::Move(place);
Expand All @@ -683,22 +677,19 @@ where
let ptr_ty = tcx.mk_ptr(ty::TypeAndMut { ty: ety, mutbl: hir::Mutability::Mut });
let ptr = Place::from(self.new_temp(ptr_ty));
let can_go = Place::from(self.new_temp(tcx.types.bool));

let one = self.constant_usize(1);
let (ptr_next, cur_next) = if ptr_based {
(
Rvalue::Use(copy(cur.into())),
Rvalue::BinaryOp(BinOp::Offset, Box::new((move_(cur.into()), one))),
)
} else {
(
Rvalue::AddressOf(Mutability::Mut, tcx.mk_place_index(self.place, cur)),
Rvalue::BinaryOp(BinOp::Add, Box::new((move_(cur.into()), one))),
)
};

let drop_block = BasicBlockData {
statements: vec![self.assign(ptr, ptr_next), self.assign(Place::from(cur), cur_next)],
statements: vec![
self.assign(
ptr,
Rvalue::AddressOf(Mutability::Mut, tcx.mk_place_index(self.place, cur)),
),
self.assign(
cur.into(),
Rvalue::BinaryOp(BinOp::Add, Box::new((move_(cur.into()), one))),
),
],
is_cleanup: unwind.is_cleanup(),
terminator: Some(Terminator {
source_info: self.source_info,
Expand All @@ -711,10 +702,7 @@ where
let loop_block = BasicBlockData {
statements: vec![self.assign(
can_go,
Rvalue::BinaryOp(
BinOp::Eq,
Box::new((copy(Place::from(cur)), copy(length_or_end))),
),
Rvalue::BinaryOp(BinOp::Eq, Box::new((copy(Place::from(cur)), copy(len.into())))),
)],
is_cleanup: unwind.is_cleanup(),
terminator: Some(Terminator {
Expand All @@ -738,13 +726,6 @@ where

fn open_drop_for_array(&mut self, ety: Ty<'tcx>, opt_size: Option<u64>) -> BasicBlock {
debug!("open_drop_for_array({:?}, {:?})", ety, opt_size);

// if size_of::<ety>() == 0 {
// index_based_loop
// } else {
// ptr_based_loop
// }

let tcx = self.tcx();

if let Some(size) = opt_size {
Expand All @@ -770,86 +751,36 @@ where
}
}

let move_ = |place: Place<'tcx>| Operand::Move(place);
let elem_size = Place::from(self.new_temp(tcx.types.usize));
let len = Place::from(self.new_temp(tcx.types.usize));

let base_block = BasicBlockData {
statements: vec![
self.assign(elem_size, Rvalue::NullaryOp(NullOp::SizeOf, ety)),
self.assign(len, Rvalue::Len(self.place)),
],
is_cleanup: self.unwind.is_cleanup(),
terminator: Some(Terminator {
source_info: self.source_info,
kind: TerminatorKind::SwitchInt {
discr: move_(elem_size),
targets: SwitchTargets::static_if(
0,
self.drop_loop_pair(ety, false, len),
self.drop_loop_pair(ety, true, len),
),
},
}),
};
self.elaborator.patch().new_block(base_block)
self.drop_loop_pair(ety)
}

/// Creates 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);
/// in the case of 1 panic.
fn drop_loop_pair(&mut self, ety: Ty<'tcx>) -> BasicBlock {
debug!("drop_loop_pair({:?})", ety);
let tcx = self.tcx();
let iter_ty = if ptr_based { tcx.mk_mut_ptr(ety) } else { tcx.types.usize };
let len = self.new_temp(tcx.types.usize);
let cur = self.new_temp(tcx.types.usize);

let cur = self.new_temp(iter_ty);
let length_or_end = if ptr_based { Place::from(self.new_temp(iter_ty)) } else { length };
let unwind =
self.unwind.map(|unwind| self.drop_loop(unwind, cur, len, ety, Unwind::InCleanup));

let unwind = self.unwind.map(|unwind| {
self.drop_loop(unwind, cur, length_or_end, ety, Unwind::InCleanup, ptr_based)
});
let loop_block = self.drop_loop(self.succ, cur, len, ety, unwind);

let loop_block = self.drop_loop(self.succ, cur, length_or_end, ety, unwind, ptr_based);

let cur = Place::from(cur);
let drop_block_stmts = if ptr_based {
let tmp_ty = tcx.mk_mut_ptr(self.place_ty(self.place));
let tmp = Place::from(self.new_temp(tmp_ty));
// tmp = &raw mut P;
// cur = tmp as *mut T;
// end = Offset(cur, len);
let mir_cast_kind = ty::cast::mir_cast_kind(iter_ty, tmp_ty);
vec![
self.assign(tmp, Rvalue::AddressOf(Mutability::Mut, self.place)),
self.assign(cur, Rvalue::Cast(mir_cast_kind, Operand::Move(tmp), iter_ty)),
self.assign(
length_or_end,
Rvalue::BinaryOp(
BinOp::Offset,
Box::new((Operand::Copy(cur), Operand::Move(length))),
),
),
]
} else {
// 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,
let zero = self.constant_usize(0);
let block = BasicBlockData {
statements: vec![
self.assign(len.into(), Rvalue::Len(self.place)),
self.assign(cur.into(), Rvalue::Use(zero)),
],
is_cleanup: unwind.is_cleanup(),
terminator: Some(Terminator {
source_info: self.source_info,
kind: TerminatorKind::Goto { target: loop_block },
}),
});
};

let drop_block = self.elaborator.patch().new_block(block);
// 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, self.succ, unwind)
Expand Down
80 changes: 17 additions & 63 deletions ...mir-opt/slice_drop_shim.core.ptr-drop_in_place.[String].AddMovesForPackedDrops.before.mir
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,21 +4,13 @@ fn std::ptr::drop_in_place(_1: *mut [String]) -> () {
let mut _0: (); // return place in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _2: usize; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _3: usize; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _4: usize; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _5: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _6: bool; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _7: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _8: bool; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _9: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _10: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _11: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _12: bool; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _13: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _14: bool; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _15: *mut [std::string::String]; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _4: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _5: bool; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _6: *mut std::string::String; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
let mut _7: bool; // in scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56

bb0: {
goto -> bb15; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
goto -> bb8; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb1: {
Expand All @@ -30,72 +22,34 @@ fn std::ptr::drop_in_place(_1: *mut [String]) -> () {
}

bb3 (cleanup): {
_5 = &raw mut (*_1)[_4]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_4 = Add(move _4, const 1_usize); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
drop((*_5)) -> bb4; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_4 = &raw mut (*_1)[_3]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_3 = Add(move _3, const 1_usize); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
drop((*_4)) -> bb4; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb4 (cleanup): {
_6 = Eq(_4, _3); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
switchInt(move _6) -> [0: bb3, otherwise: bb2]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_5 = Eq(_3, _2); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
switchInt(move _5) -> [0: bb3, otherwise: bb2]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb5: {
_7 = &raw mut (*_1)[_4]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_4 = Add(move _4, const 1_usize); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
drop((*_7)) -> [return: bb6, unwind: bb4]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_6 = &raw mut (*_1)[_3]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_3 = Add(move _3, const 1_usize); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
drop((*_6)) -> [return: bb6, unwind: bb4]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb6: {
_8 = Eq(_4, _3); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
switchInt(move _8) -> [0: bb5, otherwise: bb1]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_7 = Eq(_3, _2); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
switchInt(move _7) -> [0: bb5, otherwise: bb1]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb7: {
_4 = const 0_usize; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_2 = Len((*_1)); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_3 = const 0_usize; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
goto -> bb6; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb8: {
goto -> bb7; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb9 (cleanup): {
_11 = _9; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_9 = Offset(move _9, const 1_usize); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
drop((*_11)) -> bb10; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb10 (cleanup): {
_12 = Eq(_9, _10); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
switchInt(move _12) -> [0: bb9, otherwise: bb2]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb11: {
_13 = _9; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_9 = Offset(move _9, const 1_usize); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
drop((*_13)) -> [return: bb12, unwind: bb10]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb12: {
_14 = Eq(_9, _10); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
switchInt(move _14) -> [0: bb11, otherwise: bb1]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb13: {
_15 = &raw mut (*_1); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_9 = move _15 as *mut std::string::String (PtrToPtr); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_10 = Offset(_9, move _3); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
goto -> bb12; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb14: {
goto -> bb13; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}

bb15: {
_2 = SizeOf(std::string::String); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
_3 = Len((*_1)); // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
switchInt(move _2) -> [0: bb8, otherwise: bb14]; // scope 0 at $SRC_DIR/core/src/ptr/mod.rs:+0:1: +0:56
}
}

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