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Polished documentation, removed not-so-useful-anymore traces, and added some doc comments in mir/transform/const_prop.rs

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This commit is contained in:
Félix Fischer 2020-04-22 22:43:52 -04:00
parent 05d7a60ff8
commit 16ebaf9273
1 changed files with 13 additions and 6 deletions
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19
src/librustc_mir/transform/const_prop.rs
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@ -446,6 +446,7 @@ fn use_ecx<F, T>(&mut self, f: F) -> Option<T>
}
}
/// Returns the value, if any, of evaluating `c`.
fn eval_constant(&mut self, c: &Constant<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
// FIXME we need to revisit this for #67176
if c.needs_subst() {
@ -486,11 +487,14 @@ fn eval_constant(&mut self, c: &Constant<'tcx>, source_info: SourceInfo) -> Opti
}
}
/// Returns the value, if any, of evaluating `place`.
fn eval_place(&mut self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
trace!("eval_place(place={:?})", place);
self.use_ecx(|this| this.ecx.eval_place_to_op(place, None))
}
/// Returns the value, if any, of evaluating `op`. Calls upon `eval_constant`
/// or `eval_place`, depending on the variant of `Operand` used.
fn eval_operand(&mut self, op: &Operand<'tcx>, source_info: SourceInfo) -> Option<OpTy<'tcx>> {
match *op {
Operand::Constant(ref c) => self.eval_constant(c, source_info),
@ -649,6 +653,7 @@ fn const_prop(
})
}
/// Creates a new `Operand::Constant` from a `Scalar` value
fn operand_from_scalar(&self, scalar: Scalar, ty: Ty<'tcx>, span: Span) -> Operand<'tcx> {
Operand::Constant(Box::new(Constant {
span,
@ -694,6 +699,7 @@ fn replace_with_const(
// Found a value represented as a pair. For now only do cont-prop if type of
// Rvalue is also a pair with two scalars. The more general case is more
// complicated to implement so we'll do it later.
// FIXME: implement the general case stated above ^.
let ty = &value.layout.ty.kind;
// Only do it for tuples
if let ty::Tuple(substs) = ty {
@ -730,6 +736,7 @@ fn replace_with_const(
}
}
/// Returns `true` if and only if this `op` should be const-propagated into.
fn should_const_prop(&mut self, op: OpTy<'tcx>) -> bool {
let mir_opt_level = self.tcx.sess.opts.debugging_opts.mir_opt_level;
@ -771,14 +778,14 @@ enum ConstPropMode {
struct CanConstProp {
can_const_prop: IndexVec<Local, ConstPropMode>,
// false at the beginning, once set, there are not allowed to be any more assignments
// False at the beginning. Once set, no more assignments are allowed to that local.
found_assignment: BitSet<Local>,
// Cache of locals' information
local_kinds: IndexVec<Local, LocalKind>,
}
impl CanConstProp {
/// returns true if `local` can be propagated
/// Returns true if `local` can be propagated
fn check(body: &Body<'_>) -> IndexVec<Local, ConstPropMode> {
let mut cpv = CanConstProp {
can_const_prop: IndexVec::from_elem(ConstPropMode::FullConstProp, &body.local_decls),
@ -789,8 +796,8 @@ fn check(body: &Body<'_>) -> IndexVec<Local, ConstPropMode> {
),
};
for (local, val) in cpv.can_const_prop.iter_enumerated_mut() {
// cannot use args at all
// cannot use locals because if x < y { y - x } else { x - y } would
// Cannot use args at all
// Cannot use locals because if x < y { y - x } else { x - y } would
// lint for x != y
// FIXME(oli-obk): lint variables until they are used in a condition
// FIXME(oli-obk): lint if return value is constant
@ -936,7 +943,7 @@ fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Loca
let expected = ScalarMaybeUndef::from(Scalar::from_bool(*expected));
let value_const = self.ecx.read_scalar(value).unwrap();
if expected != value_const {
// poison all places this operand references so that further code
// Poison all places this operand references so that further code
// doesn't use the invalid value
match cond {
Operand::Move(ref place) | Operand::Copy(ref place) => {
@ -1002,7 +1009,7 @@ fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Loca
}
}
}
//none of these have Operands to const-propagate
// None of these have Operands to const-propagate
TerminatorKind::Goto { .. }
| TerminatorKind::Resume
| TerminatorKind::Abort