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Add additional trace statements to the const propagator 

This makes it easier to figure out when const propagation fails.
This commit is contained in:
Wesley Wiser 2019-05-25 10:59:05 -04:00
parent 02f5786a32
commit 9bfbbd2a78
1 changed files with 11 additions and 1 deletions
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12
src/librustc_mir/transform/const_prop.rs
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@ -295,6 +295,7 @@ impl<'a, 'mir, 'tcx> ConstPropagator<'a, 'mir, 'tcx> {
} }
fn eval_place(&mut self, place: &Place<'tcx>, source_info: SourceInfo) -> Option<Const<'tcx>> { fn eval_place(&mut self, place: &Place<'tcx>, source_info: SourceInfo) -> Option<Const<'tcx>> {
trace!("eval_place(place={:?})", place);
match *place { match *place {
Place::Base(PlaceBase::Local(loc)) => self.places[loc].clone(), Place::Base(PlaceBase::Local(loc)) => self.places[loc].clone(),
Place::Projection(ref proj) => match proj.elem { Place::Projection(ref proj) => match proj.elem {
@ -515,6 +516,7 @@ impl<'a, 'mir, 'tcx> ConstPropagator<'a, 'mir, 'tcx> {
} }
fn replace_with_const(&self, rval: &mut Rvalue<'tcx>, value: Const<'tcx>, span: Span) { fn replace_with_const(&self, rval: &mut Rvalue<'tcx>, value: Const<'tcx>, span: Span) {
trace!("attepting to replace {:?} with {:?}", rval, value);
self.ecx.validate_operand( self.ecx.validate_operand(
value, value,
vec![], vec![],
@ -578,6 +580,10 @@ impl CanConstProp {
// FIXME(oli-obk): lint variables until they are used in a condition // FIXME(oli-obk): lint variables until they are used in a condition
// FIXME(oli-obk): lint if return value is constant // FIXME(oli-obk): lint if return value is constant
*val = mir.local_kind(local) == LocalKind::Temp; *val = mir.local_kind(local) == LocalKind::Temp;
if !*val {
trace!("local {:?} can't be propagated because it's not a temporary", local);
}
} }
cpv.visit_mir(mir); cpv.visit_mir(mir);
cpv.can_const_prop cpv.can_const_prop
@ -597,6 +603,7 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
// FIXME(oli-obk): we could be more powerful here, if the multiple writes // FIXME(oli-obk): we could be more powerful here, if the multiple writes
// only occur in independent execution paths // only occur in independent execution paths
MutatingUse(MutatingUseContext::Store) => if self.found_assignment[local] { MutatingUse(MutatingUseContext::Store) => if self.found_assignment[local] {
trace!("local {:?} can't be propagated because of multiple assignments", local);
self.can_const_prop[local] = false; self.can_const_prop[local] = false;
} else { } else {
self.found_assignment[local] = true self.found_assignment[local] = true
@ -608,7 +615,10 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
NonMutatingUse(NonMutatingUseContext::Projection) | NonMutatingUse(NonMutatingUseContext::Projection) |
MutatingUse(MutatingUseContext::Projection) | MutatingUse(MutatingUseContext::Projection) |
NonUse(_) => {}, NonUse(_) => {},
_ => self.can_const_prop[local] = false, _ => {
trace!("local {:?} can't be propagaged because it's used: {:?}", local, context);
self.can_const_prop[local] = false;
},
} }
} }
} }