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Merged
merged 9 commits into from
Sep 8, 2023
Merged

Improvements to dataflow const-prop #115612

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d35be6c
Do not assert in try_to_int.
cjgillot Jan 18, 2023
09ce0f6
Remove type from ScalarTy.
cjgillot Sep 5, 2023
7ef555d
Support non-trivial scalars in ConstProp.
cjgillot May 12, 2023
74a967b
Support a few more rvalues.
cjgillot Apr 15, 2023
22986b7
Implement algebraic simplifications.
cjgillot Apr 15, 2023
fc63543
Support array length.
cjgillot Apr 23, 2023
f96c6e0
Propagate PlaceElem::Index.
cjgillot Apr 23, 2023
4ad22b9
Correct comment and assumption.
cjgillot Sep 7, 2023
b7a925a
Add test where slice is a const.
cjgillot Sep 7, 2023
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5 changes: 5 additions & 0 deletions compiler/rustc_middle/src/ty/consts/int.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,11 @@ impl ScalarInt {
}
}

#[inline]
pub fn try_from_target_usize(i: impl Into<u128>, tcx: TyCtxt<'_>) -> Option<Self> {
Self::try_from_uint(i, tcx.data_layout.pointer_size)
}

#[inline]
pub fn assert_bits(self, target_size: Size) -> u128 {
self.to_bits(target_size).unwrap_or_else(|size| {
Expand Down
83 changes: 50 additions & 33 deletions compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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Expand Up @@ -193,47 +193,64 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
rvalue: &Rvalue<'tcx>,
state: &mut State<Self::Value>,
) -> ValueOrPlace<Self::Value> {
match rvalue {
Rvalue::Cast(
kind @ (CastKind::IntToInt
| CastKind::FloatToInt
| CastKind::FloatToFloat
| CastKind::IntToFloat),
operand,
ty,
) => match self.eval_operand(operand, state) {
FlatSet::Elem(op) => match kind {
CastKind::IntToInt | CastKind::IntToFloat => {
self.ecx.int_to_int_or_float(&op, *ty)
}
CastKind::FloatToInt | CastKind::FloatToFloat => {
self.ecx.float_to_float_or_int(&op, *ty)
}
_ => unreachable!(),
let val = match rvalue {
Rvalue::Cast(CastKind::IntToInt | CastKind::IntToFloat, operand, ty) => {
match self.eval_operand(operand, state) {
FlatSet::Elem(op) => self
.ecx
.int_to_int_or_float(&op, *ty)
.map_or(FlatSet::Top, |result| self.wrap_immediate(result)),
FlatSet::Bottom => FlatSet::Bottom,
FlatSet::Top => FlatSet::Top,
}
.map(|result| ValueOrPlace::Value(self.wrap_immediate(result)))
.unwrap_or(ValueOrPlace::TOP),
_ => ValueOrPlace::TOP,
},
}
Rvalue::Cast(CastKind::FloatToInt | CastKind::FloatToFloat, operand, ty) => {
match self.eval_operand(operand, state) {
FlatSet::Elem(op) => self
.ecx
.float_to_float_or_int(&op, *ty)
.map_or(FlatSet::Top, |result| self.wrap_immediate(result)),
FlatSet::Bottom => FlatSet::Bottom,
FlatSet::Top => FlatSet::Top,
}
}
Rvalue::Cast(CastKind::Transmute, operand, _) => {
match self.eval_operand(operand, state) {
FlatSet::Elem(op) => self.wrap_immediate(*op),
FlatSet::Bottom => FlatSet::Bottom,
FlatSet::Top => FlatSet::Top,
}
Comment on lines +248 to +252
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FlatSet should probably have a map method

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The use case is so rare, I'm not sure it's worth it.

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not important, just saw 3 occurrences of this code snippet ^^

}
Rvalue::BinaryOp(op, box (left, right)) => {
// Overflows must be ignored here.
let (val, _overflow) = self.binary_op(state, *op, left, right);
ValueOrPlace::Value(val)
val
}
Rvalue::UnaryOp(op, operand) => match self.eval_operand(operand, state) {
FlatSet::Elem(value) => self
.ecx
.unary_op(*op, &value)
.map(|val| ValueOrPlace::Value(self.wrap_immty(val)))
.unwrap_or(ValueOrPlace::Value(FlatSet::Top)),
FlatSet::Bottom => ValueOrPlace::Value(FlatSet::Bottom),
FlatSet::Top => ValueOrPlace::Value(FlatSet::Top),
FlatSet::Elem(value) => {
self.ecx.unary_op(*op, &value).map_or(FlatSet::Top, |val| self.wrap_immty(val))
}
FlatSet::Bottom => FlatSet::Bottom,
FlatSet::Top => FlatSet::Top,
},
Rvalue::Discriminant(place) => {
ValueOrPlace::Value(state.get_discr(place.as_ref(), self.map()))
Rvalue::NullaryOp(null_op, ty) => {
let Ok(layout) = self.tcx.layout_of(self.param_env.and(*ty)) else {
return ValueOrPlace::Value(FlatSet::Top);
};
let val = match null_op {
NullOp::SizeOf if layout.is_sized() => layout.size.bytes(),
NullOp::AlignOf if layout.is_sized() => layout.align.abi.bytes(),
NullOp::OffsetOf(fields) => layout
.offset_of_subfield(&self.ecx, fields.iter().map(|f| f.index()))
.bytes(),
_ => return ValueOrPlace::Value(FlatSet::Top),
};
ScalarInt::try_from_target_usize(val, self.tcx).map_or(FlatSet::Top, FlatSet::Elem)
}
_ => self.super_rvalue(rvalue, state),
}
Rvalue::Discriminant(place) => state.get_discr(place.as_ref(), self.map()),
_ => return self.super_rvalue(rvalue, state),
};
ValueOrPlace::Value(val)
}

fn handle_constant(
Expand Down
76 changes: 76 additions & 0 deletions tests/mir-opt/dataflow-const-prop/offset_of.concrete.DataflowConstProp.panic-abort.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,76 @@
- // MIR for `concrete` before DataflowConstProp
+ // MIR for `concrete` after DataflowConstProp

fn concrete() -> () {
let mut _0: ();
let _1: usize;
let mut _2: usize;
let mut _4: usize;
let mut _6: usize;
let mut _8: usize;
scope 1 {
debug x => _1;
let _3: usize;
scope 2 {
debug y => _3;
let _5: usize;
scope 3 {
debug z0 => _5;
let _7: usize;
scope 4 {
debug z1 => _7;
}
}
}
}

bb0: {
StorageLive(_1);
StorageLive(_2);
- _2 = OffsetOf(Alpha, [0]);
- _1 = must_use::<usize>(move _2) -> [return: bb1, unwind unreachable];
+ _2 = const 4_usize;
+ _1 = must_use::<usize>(const 4_usize) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_2);
StorageLive(_3);
StorageLive(_4);
- _4 = OffsetOf(Alpha, [1]);
- _3 = must_use::<usize>(move _4) -> [return: bb2, unwind unreachable];
+ _4 = const 0_usize;
+ _3 = must_use::<usize>(const 0_usize) -> [return: bb2, unwind unreachable];
}

bb2: {
StorageDead(_4);
StorageLive(_5);
StorageLive(_6);
- _6 = OffsetOf(Alpha, [2, 0]);
- _5 = must_use::<usize>(move _6) -> [return: bb3, unwind unreachable];
+ _6 = const 2_usize;
+ _5 = must_use::<usize>(const 2_usize) -> [return: bb3, unwind unreachable];
}

bb3: {
StorageDead(_6);
StorageLive(_7);
StorageLive(_8);
- _8 = OffsetOf(Alpha, [2, 1]);
- _7 = must_use::<usize>(move _8) -> [return: bb4, unwind unreachable];
+ _8 = const 3_usize;
+ _7 = must_use::<usize>(const 3_usize) -> [return: bb4, unwind unreachable];
}

bb4: {
StorageDead(_8);
_0 = const ();
StorageDead(_7);
StorageDead(_5);
StorageDead(_3);
StorageDead(_1);
return;
}
}

76 changes: 76 additions & 0 deletions tests/mir-opt/dataflow-const-prop/offset_of.concrete.DataflowConstProp.panic-unwind.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,76 @@
- // MIR for `concrete` before DataflowConstProp
+ // MIR for `concrete` after DataflowConstProp

fn concrete() -> () {
let mut _0: ();
let _1: usize;
let mut _2: usize;
let mut _4: usize;
let mut _6: usize;
let mut _8: usize;
scope 1 {
debug x => _1;
let _3: usize;
scope 2 {
debug y => _3;
let _5: usize;
scope 3 {
debug z0 => _5;
let _7: usize;
scope 4 {
debug z1 => _7;
}
}
}
}

bb0: {
StorageLive(_1);
StorageLive(_2);
- _2 = OffsetOf(Alpha, [0]);
- _1 = must_use::<usize>(move _2) -> [return: bb1, unwind continue];
+ _2 = const 4_usize;
+ _1 = must_use::<usize>(const 4_usize) -> [return: bb1, unwind continue];
}

bb1: {
StorageDead(_2);
StorageLive(_3);
StorageLive(_4);
- _4 = OffsetOf(Alpha, [1]);
- _3 = must_use::<usize>(move _4) -> [return: bb2, unwind continue];
+ _4 = const 0_usize;
+ _3 = must_use::<usize>(const 0_usize) -> [return: bb2, unwind continue];
}

bb2: {
StorageDead(_4);
StorageLive(_5);
StorageLive(_6);
- _6 = OffsetOf(Alpha, [2, 0]);
- _5 = must_use::<usize>(move _6) -> [return: bb3, unwind continue];
+ _6 = const 2_usize;
+ _5 = must_use::<usize>(const 2_usize) -> [return: bb3, unwind continue];
}

bb3: {
StorageDead(_6);
StorageLive(_7);
StorageLive(_8);
- _8 = OffsetOf(Alpha, [2, 1]);
- _7 = must_use::<usize>(move _8) -> [return: bb4, unwind continue];
+ _8 = const 3_usize;
+ _7 = must_use::<usize>(const 3_usize) -> [return: bb4, unwind continue];
}

bb4: {
StorageDead(_8);
_0 = const ();
StorageDead(_7);
StorageDead(_5);
StorageDead(_3);
StorageDead(_1);
return;
}
}

72 changes: 72 additions & 0 deletions tests/mir-opt/dataflow-const-prop/offset_of.generic.DataflowConstProp.panic-abort.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,72 @@
- // MIR for `generic` before DataflowConstProp
+ // MIR for `generic` after DataflowConstProp

fn generic() -> () {
let mut _0: ();
let _1: usize;
let mut _2: usize;
let mut _4: usize;
let mut _6: usize;
let mut _8: usize;
scope 1 {
debug gx => _1;
let _3: usize;
scope 2 {
debug gy => _3;
let _5: usize;
scope 3 {
debug dx => _5;
let _7: usize;
scope 4 {
debug dy => _7;
}
}
}
}

bb0: {
StorageLive(_1);
StorageLive(_2);
_2 = OffsetOf(Gamma<T>, [0]);
_1 = must_use::<usize>(move _2) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_2);
StorageLive(_3);
StorageLive(_4);
_4 = OffsetOf(Gamma<T>, [1]);
_3 = must_use::<usize>(move _4) -> [return: bb2, unwind unreachable];
}

bb2: {
StorageDead(_4);
StorageLive(_5);
StorageLive(_6);
- _6 = OffsetOf(Delta<T>, [1]);
- _5 = must_use::<usize>(move _6) -> [return: bb3, unwind unreachable];
+ _6 = const 0_usize;
+ _5 = must_use::<usize>(const 0_usize) -> [return: bb3, unwind unreachable];
}

bb3: {
StorageDead(_6);
StorageLive(_7);
StorageLive(_8);
- _8 = OffsetOf(Delta<T>, [2]);
- _7 = must_use::<usize>(move _8) -> [return: bb4, unwind unreachable];
+ _8 = const 2_usize;
+ _7 = must_use::<usize>(const 2_usize) -> [return: bb4, unwind unreachable];
}

bb4: {
StorageDead(_8);
_0 = const ();
StorageDead(_7);
StorageDead(_5);
StorageDead(_3);
StorageDead(_1);
return;
}
}

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