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Use iterator instead of recursion in codegen_place #91278

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Jan 19, 2022
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Use iterator instead of recursion in codegen_place #91278

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143 changes: 67 additions & 76 deletions compiler/rustc_codegen_ssa/src/mir/place.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -429,87 +429,78 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
let cx = self.cx;
let tcx = self.cx.tcx();

let result = match place_ref {
mir::PlaceRef { local, projection: [] } => match self.locals[local] {
LocalRef::Place(place) => {
return place;
}
LocalRef::UnsizedPlace(place) => {
return bx.load_operand(place).deref(cx);
}
LocalRef::Operand(..) => {
let mut base = 0;
let mut cg_base = match self.locals[place_ref.local] {
LocalRef::Place(place) => place,
LocalRef::UnsizedPlace(place) => bx.load_operand(place).deref(cx),
LocalRef::Operand(..) => {
if let Some(elem) = place_ref
.projection
.iter()
.enumerate()
.find(|elem| matches!(elem.1, mir::ProjectionElem::Deref))
{
base = elem.0 + 1;
self.codegen_consume(
bx,
mir::PlaceRef { projection: &place_ref.projection[..elem.0], ..place_ref },
)
.deref(bx.cx())
} else {
bug!("using operand local {:?} as place", place_ref);
}
},
mir::PlaceRef { local, projection: [proj_base @ .., mir::ProjectionElem::Deref] } => {
// Load the pointer from its location.
self.codegen_consume(bx, mir::PlaceRef { local, projection: proj_base })
.deref(bx.cx())
}
mir::PlaceRef { local, projection: &[ref proj_base @ .., elem] } => {
// FIXME turn this recursion into iteration
let cg_base =
self.codegen_place(bx, mir::PlaceRef { local, projection: proj_base });

match elem {
mir::ProjectionElem::Deref => bug!(),
mir::ProjectionElem::Field(ref field, _) => {
cg_base.project_field(bx, field.index())
}
mir::ProjectionElem::Index(index) => {
let index = &mir::Operand::Copy(mir::Place::from(index));
let index = self.codegen_operand(bx, index);
let llindex = index.immediate();
cg_base.project_index(bx, llindex)
}
mir::ProjectionElem::ConstantIndex {
offset,
from_end: false,
min_length: _,
} => {
let lloffset = bx.cx().const_usize(offset as u64);
cg_base.project_index(bx, lloffset)
}
mir::ProjectionElem::ConstantIndex {
offset,
from_end: true,
min_length: _,
} => {
let lloffset = bx.cx().const_usize(offset as u64);
let lllen = cg_base.len(bx.cx());
let llindex = bx.sub(lllen, lloffset);
cg_base.project_index(bx, llindex)
}
mir::ProjectionElem::Subslice { from, to, from_end } => {
let mut subslice =
cg_base.project_index(bx, bx.cx().const_usize(from as u64));
let projected_ty =
PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, elem).ty;
subslice.layout = bx.cx().layout_of(self.monomorphize(projected_ty));

if subslice.layout.is_unsized() {
assert!(from_end, "slice subslices should be `from_end`");
subslice.llextra = Some(bx.sub(
cg_base.llextra.unwrap(),
bx.cx().const_usize((from as u64) + (to as u64)),
));
}

// Cast the place pointer type to the new
// array or slice type (`*[%_; new_len]`).
subslice.llval = bx.pointercast(
subslice.llval,
bx.cx().type_ptr_to(bx.cx().backend_type(subslice.layout)),
);

subslice
};
for elem in place_ref.projection[base..].iter() {
cg_base = match elem.clone() {
mir::ProjectionElem::Deref => bx.load_operand(cg_base).deref(bx.cx()),
mir::ProjectionElem::Field(ref field, _) => {
cg_base.project_field(bx, field.index())
}
mir::ProjectionElem::Index(index) => {
let index = &mir::Operand::Copy(mir::Place::from(index));
let index = self.codegen_operand(bx, index);
let llindex = index.immediate();
cg_base.project_index(bx, llindex)
}
mir::ProjectionElem::ConstantIndex { offset, from_end: false, min_length: _ } => {
let lloffset = bx.cx().const_usize(offset as u64);
cg_base.project_index(bx, lloffset)
}
mir::ProjectionElem::ConstantIndex { offset, from_end: true, min_length: _ } => {
let lloffset = bx.cx().const_usize(offset as u64);
let lllen = cg_base.len(bx.cx());
let llindex = bx.sub(lllen, lloffset);
cg_base.project_index(bx, llindex)
}
mir::ProjectionElem::Subslice { from, to, from_end } => {
let mut subslice = cg_base.project_index(bx, bx.cx().const_usize(from as u64));
let projected_ty =
PlaceTy::from_ty(cg_base.layout.ty).projection_ty(tcx, elem.clone()).ty;
subslice.layout = bx.cx().layout_of(self.monomorphize(projected_ty));

if subslice.layout.is_unsized() {
assert!(from_end, "slice subslices should be `from_end`");
subslice.llextra = Some(bx.sub(
cg_base.llextra.unwrap(),
bx.cx().const_usize((from as u64) + (to as u64)),
));
}
mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),

// Cast the place pointer type to the new
// array or slice type (`*[%_; new_len]`).
subslice.llval = bx.pointercast(
subslice.llval,
bx.cx().type_ptr_to(bx.cx().backend_type(subslice.layout)),
);

subslice
}
}
};
debug!("codegen_place(place={:?}) => {:?}", place_ref, result);
result
mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),
};
}
debug!("codegen_place(place={:?}) => {:?}", place_ref, cg_base);
cg_base
}

pub fn monomorphized_place_ty(&self, place_ref: mir::PlaceRef<'tcx>) -> Ty<'tcx> {
Expand Down