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[mir-opt] Run SimplifyLocals to a fixedpoint and handle most rvalues #70755

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merged 5 commits into from
Apr 16, 2020
Merged

[mir-opt] Run SimplifyLocals to a fixedpoint and handle most rvalues #70755

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0e0a71a
Add test case
wesleywiser Apr 3, 2020
7c0802b
Remove other Rvalues
wesleywiser Apr 3, 2020
de3cf6e
Run `SimplifyLocals` iteratively until we get to a fixedpoint
wesleywiser Apr 4, 2020
da8f3bb
Directly modify the `used_locals` vec
wesleywiser Apr 14, 2020
9666d31
Respond to code review feedback
wesleywiser Apr 16, 2020
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42 changes: 30 additions & 12 deletions src/librustc_mir/transform/simplify.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -368,21 +368,39 @@ impl<'a, 'tcx> Visitor<'tcx> for DeclMarker<'a, 'tcx> {
if location.statement_index != block.statements.len() {
let stmt = &block.statements[location.statement_index];

fn can_skip_constant(c: &ty::Const<'tcx>) -> bool {
// Keep assignments from unevaluated constants around, since the
// evaluation may report errors, even if the use of the constant
// is dead code.
!matches!(c.val, ty::ConstKind::Unevaluated(..))
}

fn can_skip_operand(o: &Operand<'_>) -> bool {
match o {
Operand::Copy(p) | Operand::Move(p) => !p.is_indirect(),
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Operand::Constant(c) => can_skip_constant(c.literal),
}
}

if let StatementKind::Assign(box (dest, rvalue)) = &stmt.kind {
if !dest.is_indirect() && dest.local == *local {
if let Rvalue::Use(Operand::Constant(c)) = rvalue {
match c.literal.val {
// Keep assignments from unevaluated constants around, since the
// evaluation may report errors, even if the use of the constant
// is dead code.
ty::ConstKind::Unevaluated(..) => {}
_ => {
trace!("skipping store of const value {:?} to {:?}", c, dest);
return;
}
let can_skip = match rvalue {
Rvalue::Use(op) => can_skip_operand(op),
Rvalue::Discriminant(_) => true,
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Should this use !place.is_indirect()?

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I think eliminating a read of an indirect place's discriminant is ok in the same way removing a read of its address is. Is there a situation you're thinking of where that wouldn't be true?

Rvalue::BinaryOp(_, l, r) | Rvalue::CheckedBinaryOp(_, l, r) => {
can_skip_operand(l) && can_skip_operand(r)
}
} else if let Rvalue::Discriminant(d) = rvalue {
trace!("skipping store of discriminant value {:?} to {:?}", d, dest);
Rvalue::Repeat(op, c) => can_skip_operand(op) && can_skip_constant(c),
Rvalue::AddressOf(_, _) => true,
Rvalue::Len(_) => true,
Rvalue::UnaryOp(_, op) => can_skip_operand(op),
Rvalue::Aggregate(_, operands) => operands.iter().all(can_skip_operand),

_ => false,
};

if can_skip {
trace!("skipping store of {:?} to {:?}", rvalue, dest);
return;
}
}
Expand Down
16 changes: 8 additions & 8 deletions src/test/mir-opt/const_allocation3/32bit/rustc.main.ConstProp.after.mir
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Expand Up @@ -30,30 +30,30 @@ fn main() -> () {
}

alloc0 (static: FOO, size: 4, align: 4) {
╾alloc10+0╼ │ ╾──╼
╾alloc9+0─╼ │ ╾──╼
}

alloc10 (size: 168, align: 1) {
alloc9 (size: 168, align: 1) {
0x00 │ ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab │ ................
0x10 │ ab ab ab ab ab ab ab ab ab ab ab ab ╾alloc5+0─╼ │ ............╾──╼
0x10 │ ab ab ab ab ab ab ab ab ab ab ab ab ╾alloc4+0─╼ │ ............╾──╼
0x20 │ 01 ef cd ab 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x30 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x40 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x50 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x60 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x70 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x80 │ 00 00 00 00 00 00 00 00 00 00 ╾alloc7+0─╼ 00 00 │ ..........╾──╼..
0x90 │ ╾alloc8+99╼ 00 00 00 00 00 00 00 00 00 00 00 00 │ ╾──╼............
0x80 │ 00 00 00 00 00 00 00 00 00 00 ╾alloc6+0─╼ 00 00 │ ..........╾──╼..
0x90 │ ╾alloc7+99╼ 00 00 00 00 00 00 00 00 00 00 00 00 │ ╾──╼............
0xa0 │ 00 00 00 00 00 00 00 00 │ ........
}

alloc5 (size: 4, align: 4) {
alloc4 (size: 4, align: 4) {
2a 00 00 00 │ *...
}

alloc7 (fn: main)
alloc6 (fn: main)

alloc8 (size: 100, align: 1) {
alloc7 (size: 100, align: 1) {
0x00 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x10 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x20 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
Expand Down
14 changes: 7 additions & 7 deletions src/test/mir-opt/const_allocation3/64bit/rustc.main.ConstProp.after.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -30,31 +30,31 @@ fn main() -> () {
}

alloc0 (static: FOO, size: 8, align: 8) {
╾──────alloc10+0──────╼ │ ╾──────╼
╾──────alloc9+0───────╼ │ ╾──────╼
}

alloc10 (size: 180, align: 1) {
alloc9 (size: 180, align: 1) {
0x00 │ ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab ab │ ................
0x10 │ ab ab ab ab ab ab ab ab ab ab ab ab ╾─alloc5+0─ │ ............╾───
0x10 │ ab ab ab ab ab ab ab ab ab ab ab ab ╾─alloc4+0─ │ ............╾───
0x20 │ ──────────╼ 01 ef cd ab 00 00 00 00 00 00 00 00 │ ───╼............
0x30 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x40 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x50 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x60 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x70 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x80 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ╾──── │ ..............╾─
0x90 │ ────alloc7+0────╼ 00 00 ╾──────alloc8+99──────╼ │ ─────╼..╾──────╼
0x90 │ ────alloc6+0────╼ 00 00 ╾──────alloc7+99──────╼ │ ─────╼..╾──────╼
0xa0 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0xb0 │ 00 00 00 00 │ ....
}

alloc5 (size: 4, align: 4) {
alloc4 (size: 4, align: 4) {
2a 00 00 00 │ *...
}

alloc7 (fn: main)
alloc6 (fn: main)

alloc8 (size: 100, align: 1) {
alloc7 (size: 100, align: 1) {
0x00 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x10 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
0x20 │ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 │ ................
Expand Down
60 changes: 10 additions & 50 deletions ...test/mir-opt/const_prop/optimizes_into_variable/32bit/rustc.main.SimplifyLocals.after.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -3,15 +3,14 @@
fn main() -> () {
let mut _0: (); // return place in scope 0 at $DIR/optimizes_into_variable.rs:11:11: 11:11
let _1: i32; // in scope 0 at $DIR/optimizes_into_variable.rs:12:9: 12:10
let mut _3: [i32; 6]; // in scope 0 at $DIR/optimizes_into_variable.rs:13:13: 13:31
scope 1 {
debug x => _1; // in scope 1 at $DIR/optimizes_into_variable.rs:12:9: 12:10
let _2: i32; // in scope 1 at $DIR/optimizes_into_variable.rs:13:9: 13:10
scope 2 {
debug y => _2; // in scope 2 at $DIR/optimizes_into_variable.rs:13:9: 13:10
let _4: u32; // in scope 2 at $DIR/optimizes_into_variable.rs:14:9: 14:10
let _3: u32; // in scope 2 at $DIR/optimizes_into_variable.rs:14:9: 14:10
scope 3 {
debug z => _4; // in scope 3 at $DIR/optimizes_into_variable.rs:14:9: 14:10
debug z => _3; // in scope 3 at $DIR/optimizes_into_variable.rs:14:9: 14:10
}
}
}
Expand All @@ -26,70 +25,31 @@ fn main() -> () {
// + span: $DIR/optimizes_into_variable.rs:12:13: 12:18
// + literal: Const { ty: i32, val: Value(Scalar(0x00000004)) }
StorageLive(_2); // bb0[2]: scope 1 at $DIR/optimizes_into_variable.rs:13:9: 13:10
StorageLive(_3); // bb0[3]: scope 1 at $DIR/optimizes_into_variable.rs:13:13: 13:31
_3 = [const 0i32, const 1i32, const 2i32, const 3i32, const 4i32, const 5i32]; // bb0[4]: scope 1 at $DIR/optimizes_into_variable.rs:13:13: 13:31
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000000))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:13:14: 13:15
// + literal: Const { ty: i32, val: Value(Scalar(0x00000000)) }
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000001))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:13:17: 13:18
// + literal: Const { ty: i32, val: Value(Scalar(0x00000001)) }
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000002))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:13:20: 13:21
// + literal: Const { ty: i32, val: Value(Scalar(0x00000002)) }
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000003))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:13:23: 13:24
// + literal: Const { ty: i32, val: Value(Scalar(0x00000003)) }
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000004))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:13:26: 13:27
// + literal: Const { ty: i32, val: Value(Scalar(0x00000004)) }
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000005))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:13:29: 13:30
// + literal: Const { ty: i32, val: Value(Scalar(0x00000005)) }
_2 = const 3i32; // bb0[5]: scope 1 at $DIR/optimizes_into_variable.rs:13:13: 13:34
_2 = const 3i32; // bb0[3]: scope 1 at $DIR/optimizes_into_variable.rs:13:13: 13:34
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000003))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:13:13: 13:34
// + literal: Const { ty: i32, val: Value(Scalar(0x00000003)) }
StorageDead(_3); // bb0[6]: scope 1 at $DIR/optimizes_into_variable.rs:13:34: 13:35
StorageLive(_4); // bb0[7]: scope 2 at $DIR/optimizes_into_variable.rs:14:9: 14:10
_4 = const 42u32; // bb0[8]: scope 2 at $DIR/optimizes_into_variable.rs:14:13: 14:38
StorageLive(_3); // bb0[4]: scope 2 at $DIR/optimizes_into_variable.rs:14:9: 14:10
_3 = const 42u32; // bb0[5]: scope 2 at $DIR/optimizes_into_variable.rs:14:13: 14:38
// ty::Const
// + ty: u32
// + val: Value(Scalar(0x0000002a))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:14:13: 14:38
// + literal: Const { ty: u32, val: Value(Scalar(0x0000002a)) }
_0 = const (); // bb0[9]: scope 0 at $DIR/optimizes_into_variable.rs:11:11: 15:2
_0 = const (); // bb0[6]: scope 0 at $DIR/optimizes_into_variable.rs:11:11: 15:2
// ty::Const
// + ty: ()
// + val: Value(Scalar(<ZST>))
// mir::Constant
// + span: $DIR/optimizes_into_variable.rs:11:11: 15:2
// + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
StorageDead(_4); // bb0[10]: scope 2 at $DIR/optimizes_into_variable.rs:15:1: 15:2
StorageDead(_2); // bb0[11]: scope 1 at $DIR/optimizes_into_variable.rs:15:1: 15:2
StorageDead(_1); // bb0[12]: scope 0 at $DIR/optimizes_into_variable.rs:15:1: 15:2
return; // bb0[13]: scope 0 at $DIR/optimizes_into_variable.rs:15:2: 15:2
StorageDead(_3); // bb0[7]: scope 2 at $DIR/optimizes_into_variable.rs:15:1: 15:2
StorageDead(_2); // bb0[8]: scope 1 at $DIR/optimizes_into_variable.rs:15:1: 15:2
StorageDead(_1); // bb0[9]: scope 0 at $DIR/optimizes_into_variable.rs:15:1: 15:2
return; // bb0[10]: scope 0 at $DIR/optimizes_into_variable.rs:15:2: 15:2
}
}
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