From 9bfbbd2a786b7d69908f25e5d1f4170316f38726 Mon Sep 17 00:00:00 2001
From: Wesley Wiser <wwiser@gmail.com>
Date: Sat, 25 May 2019 10:59:05 -0400
Subject: [PATCH] Add additional trace statements to the const propagator
This makes it easier to figure out when const propagation fails.
---
src/librustc_mir/transform/const_prop.rs | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index 8f3dd72c4f245..718cb5ce527ec 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -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>> {
+ trace!("eval_place(place={:?})", place);
match *place {
Place::Base(PlaceBase::Local(loc)) => self.places[loc].clone(),
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) {
+ trace!("attepting to replace {:?} with {:?}", rval, value);
self.ecx.validate_operand(
value,
vec![],
@@ -578,6 +580,10 @@ impl CanConstProp {
// FIXME(oli-obk): lint variables until they are used in a condition
// FIXME(oli-obk): lint if return value is constant
*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.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
// only occur in independent execution paths
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;
} else {
self.found_assignment[local] = true
@@ -608,7 +615,10 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
NonMutatingUse(NonMutatingUseContext::Projection) |
MutatingUse(MutatingUseContext::Projection) |
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;
+ },
}
}
}