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Perform opportunistic simplifications during value numbering #111344

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Perform opportunistic simplifications during value numbering #111344

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69d51fc
Simplify operands in unions.
cjgillot Oct 31, 2023
d272ab3
Perform GVN into debuginfo.
cjgillot Jun 5, 2023
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60 changes: 54 additions & 6 deletions compiler/rustc_mir_transform/src/gvn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,9 @@ fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
state.next_opaque = None;

let reverse_postorder = body.basic_blocks.reverse_postorder().to_vec();
for dbg in body.var_debug_info.iter_mut() {
state.visit_var_debug_info(dbg);
}
for bb in reverse_postorder {
let data = &mut body.basic_blocks.as_mut_preserves_cfg()[bb];
state.visit_basic_block_data(bb, data);
Expand Down Expand Up @@ -893,6 +896,12 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
}
}

let fields: Option<Vec<_>> = fields
.iter_mut()
.map(|op| self.simplify_operand(op, location).or_else(|| self.new_opaque()))
.collect();
let fields = fields?;

let (ty, variant_index) = match *kind {
AggregateKind::Array(..) => {
assert!(!fields.is_empty());
Expand All @@ -912,12 +921,6 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
AggregateKind::Adt(_, _, _, _, Some(_)) => return None,
};

let fields: Option<Vec<_>> = fields
.iter_mut()
.map(|op| self.simplify_operand(op, location).or_else(|| self.new_opaque()))
.collect();
let fields = fields?;

if let AggregateTy::Array = ty
&& fields.len() > 4
{
Expand Down Expand Up @@ -1238,6 +1241,51 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
self.tcx
}

fn visit_var_debug_info(&mut self, var_debug_info: &mut VarDebugInfo<'tcx>) {
let mut replace_dereffed = |place: &mut Place<'tcx>| -> Option<!> {
let last_deref = place.projection.iter().rposition(|e| e == PlaceElem::Deref)?;

// Another place that holds the same value.
let mut place_ref = place.as_ref();
let mut value = self.locals[place.local]?;

for (index, &proj) in place.projection[..last_deref].iter().enumerate() {
if let Some(candidates) = self.rev_locals.get(value)
&& let Some(&local) = candidates.first()
{
place_ref = PlaceRef { local, projection: &place.projection[index..] };
}

let place_upto =
PlaceRef { local: place.local, projection: &place.projection[..index] };
if let Some(projected) = self.project(place_upto, value, proj) {
value = projected;
} else {
if place_ref.projection.len() < place.projection.len() {
*place = place_ref.project_deeper(&[], self.tcx);
}
return None;
}
}

if let Some(candidates) = self.rev_locals.get(value)
&& let Some(&local) = candidates.first()
{
let place_ref = PlaceRef { local, projection: &place.projection[last_deref..] };
*place = place_ref.project_deeper(&[], self.tcx);
}

return None;
};

match &mut var_debug_info.value {
VarDebugInfoContents::Const(_) => {}
VarDebugInfoContents::Place(place) => {
replace_dereffed(place);
}
}
}

fn visit_place(&mut self, place: &mut Place<'tcx>, _: PlaceContext, location: Location) {
self.simplify_place_projection(place, location);
}
Expand Down
3 changes: 2 additions & 1 deletion tests/mir-opt/const_prop/transmute.undef_union_as_integer.GVN.32bit.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,9 @@
StorageLive(_1);
StorageLive(_2);
- _2 = ();
- _1 = Union32 { value: move _2 };
+ _2 = const ();
_1 = Union32 { value: move _2 };
+ _1 = Union32 { value: const () };
StorageDead(_2);
_0 = move _1 as u32 (Transmute);
StorageDead(_1);
Expand Down
3 changes: 2 additions & 1 deletion tests/mir-opt/const_prop/transmute.undef_union_as_integer.GVN.64bit.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,9 @@
StorageLive(_1);
StorageLive(_2);
- _2 = ();
- _1 = Union32 { value: move _2 };
+ _2 = const ();
_1 = Union32 { value: move _2 };
+ _1 = Union32 { value: const () };
StorageDead(_2);
_0 = move _1 as u32 (Transmute);
StorageDead(_1);
Expand Down
10 changes: 3 additions & 7 deletions tests/mir-opt/dest-prop/union.main.DestinationPropagation.panic-abort.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -5,25 +5,21 @@
let mut _0: ();
let _1: main::Un;
let mut _2: u32;
let mut _3: u32;
scope 1 {
debug un => _1;
scope 3 (inlined std::mem::drop::<u32>) {
debug _x => _3;
debug _x => _2;
}
}
scope 2 (inlined val) {
}

bb0: {
StorageLive(_1);
StorageLive(_2);
_2 = const 1_u32;
_1 = Un { us: const 1_u32 };
StorageLive(_2);
_2 = (_1.0: u32);
StorageDead(_2);
StorageLive(_3);
_3 = (_1.0: u32);
StorageDead(_3);
StorageDead(_1);
return;
}
Expand Down
10 changes: 3 additions & 7 deletions tests/mir-opt/dest-prop/union.main.DestinationPropagation.panic-unwind.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -5,25 +5,21 @@
let mut _0: ();
let _1: main::Un;
let mut _2: u32;
let mut _3: u32;
scope 1 {
debug un => _1;
scope 3 (inlined std::mem::drop::<u32>) {
debug _x => _3;
debug _x => _2;
}
}
scope 2 (inlined val) {
}

bb0: {
StorageLive(_1);
StorageLive(_2);
_2 = const 1_u32;
_1 = Un { us: const 1_u32 };
StorageLive(_2);
_2 = (_1.0: u32);
StorageDead(_2);
StorageLive(_3);
_3 = (_1.0: u32);
StorageDead(_3);
StorageDead(_1);
return;
}
Expand Down
4 changes: 2 additions & 2 deletions tests/mir-opt/inline/inline_closure_captures.foo.Inline.after.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -15,8 +15,8 @@ fn foo(_1: T, _2: i32) -> (i32, T) {
debug x => _3;
scope 2 (inlined foo::<T>::{closure#0}) {
debug _q => _9;
debug q => (*((*_6).0: &i32));
debug t => (*((*_6).1: &T));
debug q => (*_10);
debug t => (*_12);
let mut _10: &i32;
let mut _11: i32;
let mut _12: &T;
Expand Down