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[mir-opt] Small ConstProp cleanup #71911

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Jun 21, 2020
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[mir-opt] Small ConstProp cleanup #71911

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c06876c
[const-prop] Remove `ConstPropMode::NoPropagation`
wesleywiser Apr 23, 2020
2f49d55
Add EMIR_MIR_FOR_EACH_BIT_WIDTH to failing test
wesleywiser May 5, 2020
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47 changes: 21 additions & 26 deletions src/librustc_mir/transform/const_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -721,8 +721,6 @@ enum ConstPropMode {
OnlyInsideOwnBlock,
/// The `Local` can be propagated into but reads cannot be propagated.
OnlyPropagateInto,
/// No propagation is allowed at all.
NoPropagation,
}

struct CanConstProp {
Expand Down Expand Up @@ -793,7 +791,7 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
"local {:?} can't be propagated because of multiple assignments",
local,
);
*other = ConstPropMode::NoPropagation;
*other = ConstPropMode::OnlyPropagateInto;
}
}
}
Expand All @@ -820,7 +818,7 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
| MutatingUse(MutatingUseContext::Borrow)
| MutatingUse(MutatingUseContext::AddressOf) => {
trace!("local {:?} can't be propagaged because it's used: {:?}", local, context);
self.can_const_prop[local] = ConstPropMode::NoPropagation;
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@oli-obk so is this the diff that caused the bug? That these uses no longer prevent propagation? Instead of duplicating that use detection by handling Ref and AddrOf ourselves, would it make more sense to continue to use this info here (or at least do so additionally)?

self.can_const_prop[local] = ConstPropMode::OnlyPropagateInto;
}
}
}
Expand Down Expand Up @@ -852,31 +850,28 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
if let Ok(place_layout) = self.tcx.layout_of(self.param_env.and(place_ty)) {
let can_const_prop = self.can_const_prop[place.local];
if let Some(()) = self.const_prop(rval, place_layout, source_info, place) {
if can_const_prop != ConstPropMode::NoPropagation {
// This will return None for variables that are from other blocks,
// so it should be okay to propagate from here on down.
if let Some(value) = self.get_const(place) {
if self.should_const_prop(value) {
trace!("replacing {:?} with {:?}", rval, value);
self.replace_with_const(rval, value, source_info);
if can_const_prop == ConstPropMode::FullConstProp
|| can_const_prop == ConstPropMode::OnlyInsideOwnBlock
{
trace!("propagated into {:?}", place);
}
}
if can_const_prop == ConstPropMode::OnlyInsideOwnBlock {
trace!(
"found local restricted to its block. Will remove it from const-prop after block is finished. Local: {:?}",
place.local
);
self.locals_of_current_block.insert(place.local);
// This will return None for variables that are from other blocks,
// so it should be okay to propagate from here on down.
if let Some(value) = self.get_const(place) {
if self.should_const_prop(value) {
trace!("replacing {:?} with {:?}", rval, value);
self.replace_with_const(rval, value, source_info);
if can_const_prop == ConstPropMode::FullConstProp
|| can_const_prop == ConstPropMode::OnlyInsideOwnBlock
{
trace!("propagated into {:?}", place);
}
}
}
if can_const_prop == ConstPropMode::OnlyPropagateInto
|| can_const_prop == ConstPropMode::NoPropagation
{
if can_const_prop == ConstPropMode::OnlyInsideOwnBlock {
trace!(
"found local restricted to its block. Will remove it from const-prop after block is finished. Local: {:?}",
place.local
);
self.locals_of_current_block.insert(place.local);
}

if can_const_prop == ConstPropMode::OnlyPropagateInto {
trace!("can't propagate into {:?}", place);
if place.local != RETURN_PLACE {
Self::remove_const(&mut self.ecx, place.local);
Expand Down
6 changes: 4 additions & 2 deletions src/test/mir-opt/const_prop/mutable_variable_aggregate_mut_ref/rustc.main.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -23,13 +23,15 @@
// + ty: i32
// + val: Value(Scalar(0x0000002a))
// mir::Constant
// + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:18: 5:20
- // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:18: 5:20
+ // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:17: 5:25
// + literal: Const { ty: i32, val: Value(Scalar(0x0000002a)) }
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x0000002b))
// mir::Constant
// + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:22: 5:24
- // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:22: 5:24
+ // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:17: 5:25
// + literal: Const { ty: i32, val: Value(Scalar(0x0000002b)) }
StorageLive(_2); // scope 1 at $DIR/mutable_variable_aggregate_mut_ref.rs:6:9: 6:10
_2 = &mut _1; // scope 1 at $DIR/mutable_variable_aggregate_mut_ref.rs:6:13: 6:19
Expand Down
9 changes: 4 additions & 5 deletions src/test/mir-opt/simplify-arm-identity/32bit/rustc.main.SimplifyArmIdentity.diff
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Expand Up @@ -39,14 +39,13 @@
}

bb1: {
((_2 as Foo).0: u8) = const 0u8; // scope 1 at $DIR/simplify-arm-identity.rs:21:21: 21:32
_2 = const Dst::Foo(0u8); // scope 1 at $DIR/simplify-arm-identity.rs:21:21: 21:32
// ty::Const
// + ty: u8
// + ty: Dst
// + val: Value(Scalar(0x00))
// mir::Constant
// + span: $DIR/simplify-arm-identity.rs:21:30: 21:31
// + literal: Const { ty: u8, val: Value(Scalar(0x00)) }
discriminant(_2) = 0; // scope 1 at $DIR/simplify-arm-identity.rs:21:21: 21:32
// + span: $DIR/simplify-arm-identity.rs:21:21: 21:32
// + literal: Const { ty: Dst, val: Value(Scalar(0x00)) }
goto -> bb4; // scope 1 at $DIR/simplify-arm-identity.rs:19:18: 22:6
}

Expand Down
9 changes: 4 additions & 5 deletions src/test/mir-opt/simplify-arm-identity/64bit/rustc.main.SimplifyArmIdentity.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -39,14 +39,13 @@
}

bb1: {
((_2 as Foo).0: u8) = const 0u8; // scope 1 at $DIR/simplify-arm-identity.rs:21:21: 21:32
_2 = const Dst::Foo(0u8); // scope 1 at $DIR/simplify-arm-identity.rs:21:21: 21:32
// ty::Const
// + ty: u8
// + ty: Dst
// + val: Value(Scalar(0x00))
// mir::Constant
// + span: $DIR/simplify-arm-identity.rs:21:30: 21:31
// + literal: Const { ty: u8, val: Value(Scalar(0x00)) }
discriminant(_2) = 0; // scope 1 at $DIR/simplify-arm-identity.rs:21:21: 21:32
// + span: $DIR/simplify-arm-identity.rs:21:21: 21:32
// + literal: Const { ty: Dst, val: Value(Scalar(0x00)) }
goto -> bb4; // scope 1 at $DIR/simplify-arm-identity.rs:19:18: 22:6
}

Expand Down
11 changes: 5 additions & 6 deletions src/test/mir-opt/simplify-arm-identity/rustc.main.SimplifyArmIdentity.diff
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Expand Up @@ -33,15 +33,14 @@
}

bb1: {
((_2 as Foo).0: u8) = const 0u8; // scope 1 at $DIR/simplify-arm-identity.rs:20:21: 20:32
_2 = const Dst::Foo(0u8); // bb1[0]: scope 1 at $DIR/simplify-arm-identity.rs:20:21: 20:32
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// ty::Const
// + ty: u8
// + ty: Dst
// + val: Value(Scalar(0x00))
// mir::Constant
// + span: $DIR/simplify-arm-identity.rs:20:30: 20:31
// + literal: Const { ty: u8, val: Value(Scalar(0x00)) }
discriminant(_2) = 0; // scope 1 at $DIR/simplify-arm-identity.rs:20:21: 20:32
goto -> bb4; // scope 1 at $DIR/simplify-arm-identity.rs:18:18: 21:6
// + span: $DIR/simplify-arm-identity.rs:20:21: 20:32
// + literal: Const { ty: Dst, val: Value(Scalar(0x00)) }
goto -> bb4; // bb1[1]: scope 1 at $DIR/simplify-arm-identity.rs:18:18: 21:6
}

bb2: {
Expand Down
1 change: 1 addition & 0 deletions src/test/mir-opt/simplify-locals-removes-unused-discriminant-reads.rs
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Expand Up @@ -9,4 +9,5 @@ fn main() {
map(None);
}

// EMIT_MIR_FOR_EACH_BIT_WIDTH
// EMIT_MIR rustc.map.SimplifyLocals.diff
8 changes: 7 additions & 1 deletion ...inant-reads/rustc.map.SimplifyLocals.diff → ...reads/32bit/rustc.map.SimplifyLocals.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,13 @@
}

bb2: {
discriminant(_0) = 0; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:17: 3:21
_0 = const std::option::Option::<std::boxed::Box<()>>::None; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:17: 3:21
// ty::Const
// + ty: std::option::Option<std::boxed::Box<()>>
// + val: Value(Scalar(0x00000000))
// mir::Constant
// + span: $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:17: 3:21
// + literal: Const { ty: std::option::Option<std::boxed::Box<()>>, val: Value(Scalar(0x00000000)) }
goto -> bb3; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:2:5: 5:6
}

Expand Down
42 changes: 42 additions & 0 deletions ...opt/simplify-locals-removes-unused-discriminant-reads/64bit/rustc.map.SimplifyLocals.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
- // MIR for `map` before SimplifyLocals
+ // MIR for `map` after SimplifyLocals

fn map(_1: std::option::Option<std::boxed::Box<()>>) -> std::option::Option<std::boxed::Box<()>> {
debug x => _1; // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:1:8: 1:9
let mut _0: std::option::Option<std::boxed::Box<()>>; // return place in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:1:31: 1:46
let mut _2: isize; // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
let _3: std::boxed::Box<()>; // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:14: 4:15
- let mut _4: std::boxed::Box<()>; // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:25: 4:26
- let mut _5: isize; // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
- let mut _6: isize; // in scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
scope 1 {
debug x => _3; // in scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:14: 4:15
}

bb0: {
_2 = discriminant(_1); // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
switchInt(move _2) -> [0isize: bb2, otherwise: bb1]; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:9: 3:13
}

bb1: {
_0 = move _1; // scope 1 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:4:20: 4:27
goto -> bb3; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:2:5: 5:6
}

bb2: {
_0 = const std::option::Option::<std::boxed::Box<()>>::None; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:17: 3:21
// ty::Const
// + ty: std::option::Option<std::boxed::Box<()>>
// + val: Value(Scalar(0x0000000000000000))
// mir::Constant
// + span: $DIR/simplify-locals-removes-unused-discriminant-reads.rs:3:17: 3:21
// + literal: Const { ty: std::option::Option<std::boxed::Box<()>>, val: Value(Scalar(0x0000000000000000)) }
goto -> bb3; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:2:5: 5:6
}

bb3: {
- _5 = discriminant(_1); // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:1: 6:2
return; // scope 0 at $DIR/simplify-locals-removes-unused-discriminant-reads.rs:6:2: 6:2
}
}