From 78a37f888a00c7406e7a54346697a41802891db7 Mon Sep 17 00:00:00 2001
From: cjkenn <cjkenn@users.noreply.github.com>
Date: Mon, 16 Nov 2020 18:09:10 -0500
Subject: [PATCH 1/7] add optimization fuel checks to some mir passes
---
compiler/rustc_mir/src/transform/const_prop.rs | 4 ++++
.../rustc_mir/src/transform/early_otherwise_branch.rs | 4 ++++
compiler/rustc_mir/src/transform/instcombine.rs | 7 +++++++
compiler/rustc_mir/src/transform/match_branches.rs | 5 +++++
.../src/transform/multiple_return_terminators.rs | 6 ++++++
compiler/rustc_mir/src/transform/nrvo.rs | 10 +++++++---
compiler/rustc_mir/src/transform/promote_consts.rs | 4 ++++
.../rustc_mir/src/transform/remove_unneeded_drops.rs | 4 ++++
compiler/rustc_mir/src/transform/unreachable_prop.rs | 6 ++++++
9 files changed, 47 insertions(+), 3 deletions(-)
diff --git a/compiler/rustc_mir/src/transform/const_prop.rs b/compiler/rustc_mir/src/transform/const_prop.rs
index aeb9920c0e321..1f266a95f03f6 100644
--- a/compiler/rustc_mir/src/transform/const_prop.rs
+++ b/compiler/rustc_mir/src/transform/const_prop.rs
@@ -89,6 +89,10 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
return;
}
+ if !tcx.consider_optimizing(|| format!("ConstantPropagation {:?} {:?}", def_id, hir_id)) {
+ return;
+ }
+
// Check if it's even possible to satisfy the 'where' clauses
// for this item.
// This branch will never be taken for any normal function.
diff --git a/compiler/rustc_mir/src/transform/early_otherwise_branch.rs b/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
index f97dcf4852df4..f91477911a489 100644
--- a/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
+++ b/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
@@ -46,6 +46,10 @@ impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch {
let should_cleanup = !opts_to_apply.is_empty();
for opt_to_apply in opts_to_apply {
+ if !tcx.consider_optimizing(|| format!("EarlyOtherwiseBranch {:?}", &opt_to_apply)) {
+ break;
+ }
+
trace!("SUCCESS: found optimization possibility to apply: {:?}", &opt_to_apply);
let statements_before =
diff --git a/compiler/rustc_mir/src/transform/instcombine.rs b/compiler/rustc_mir/src/transform/instcombine.rs
index 59b7db2431900..5a21cdc6891f4 100644
--- a/compiler/rustc_mir/src/transform/instcombine.rs
+++ b/compiler/rustc_mir/src/transform/instcombine.rs
@@ -20,6 +20,13 @@ pub struct InstCombine;
impl<'tcx> MirPass<'tcx> for InstCombine {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+ // Check for fuel here before gathering the optimization list. If we're out of fuel,
+ // we don't want to take the time to pass over the MIR only to find optimizations
+ // we won't run.
+ if !tcx.consider_optimizing(|| format!("InstCombine {:?} ", body.source.def_id())) {
+ return;
+ }
+
// First, find optimization opportunities. This is done in a pre-pass to keep the MIR
// read-only so that we can do global analyses on the MIR in the process (e.g.
// `Place::ty()`).
diff --git a/compiler/rustc_mir/src/transform/match_branches.rs b/compiler/rustc_mir/src/transform/match_branches.rs
index 82c0b924f287e..53eeecc780f6f 100644
--- a/compiler/rustc_mir/src/transform/match_branches.rs
+++ b/compiler/rustc_mir/src/transform/match_branches.rs
@@ -43,8 +43,13 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
}
let param_env = tcx.param_env(body.source.def_id());
+ let def_id = body.source.def_id();
let (bbs, local_decls) = body.basic_blocks_and_local_decls_mut();
'outer: for bb_idx in bbs.indices() {
+ if !tcx.consider_optimizing(|| format!("MatchBranchSimplification {:?} ", def_id)) {
+ continue;
+ }
+
let (discr, val, switch_ty, first, second) = match bbs[bb_idx].terminator().kind {
TerminatorKind::SwitchInt {
discr: ref discr @ (Operand::Copy(_) | Operand::Move(_)),
diff --git a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
index c37b54a3190f8..4a66bc45ae37b 100644
--- a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
+++ b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
@@ -14,6 +14,12 @@ impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
return;
}
+ if !tcx.consider_optimizing(|| {
+ format!("MultipleReturnTerminators {:?} ", body.source.def_id())
+ }) {
+ return;
+ }
+
// find basic blocks with no statement and a return terminator
let mut bbs_simple_returns = BitSet::new_empty(body.basic_blocks().len());
let bbs = body.basic_blocks_mut();
diff --git a/compiler/rustc_mir/src/transform/nrvo.rs b/compiler/rustc_mir/src/transform/nrvo.rs
index 45b906bf542d5..ce02fb261df6f 100644
--- a/compiler/rustc_mir/src/transform/nrvo.rs
+++ b/compiler/rustc_mir/src/transform/nrvo.rs
@@ -38,18 +38,22 @@ impl<'tcx> MirPass<'tcx> for RenameReturnPlace {
return;
}
+ let def_id = body.source.def_id();
let returned_local = match local_eligible_for_nrvo(body) {
Some(l) => l,
None => {
- debug!("`{:?}` was ineligible for NRVO", body.source.def_id());
+ debug!("`{:?}` was ineligible for NRVO", def_id);
return;
}
};
+ if !tcx.consider_optimizing(|| format!("RenameReturnPlace {:?}", def_id)) {
+ return;
+ }
+
debug!(
"`{:?}` was eligible for NRVO, making {:?} the return place",
- body.source.def_id(),
- returned_local
+ def_id, returned_local
);
RenameToReturnPlace { tcx, to_rename: returned_local }.visit_body(body);
diff --git a/compiler/rustc_mir/src/transform/promote_consts.rs b/compiler/rustc_mir/src/transform/promote_consts.rs
index 927aae82a36ef..0539d8fffabc8 100644
--- a/compiler/rustc_mir/src/transform/promote_consts.rs
+++ b/compiler/rustc_mir/src/transform/promote_consts.rs
@@ -60,6 +60,10 @@ impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
return;
}
+ if !tcx.consider_optimizing(|| format!("PromoteTemps {:?} ", body.source.def_id())) {
+ return;
+ }
+
let mut rpo = traversal::reverse_postorder(body);
let ccx = ConstCx::new(tcx, body);
let (temps, all_candidates) = collect_temps_and_candidates(&ccx, &mut rpo);
diff --git a/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
index aaf3ecab4dca7..2a72751071bb1 100644
--- a/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
+++ b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
@@ -11,6 +11,10 @@ pub struct RemoveUnneededDrops;
impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+ if !tcx.consider_optimizing(|| format!("RemoveUnneededDrops {:?} ", body.source.def_id())) {
+ return;
+ }
+
trace!("Running RemoveUnneededDrops on {:?}", body.source);
let mut opt_finder = RemoveUnneededDropsOptimizationFinder {
tcx,
diff --git a/compiler/rustc_mir/src/transform/unreachable_prop.rs b/compiler/rustc_mir/src/transform/unreachable_prop.rs
index f6d39dae3429e..4100a50c225b3 100644
--- a/compiler/rustc_mir/src/transform/unreachable_prop.rs
+++ b/compiler/rustc_mir/src/transform/unreachable_prop.rs
@@ -18,6 +18,12 @@ impl MirPass<'_> for UnreachablePropagation {
return;
}
+ if !tcx
+ .consider_optimizing(|| format!("UnreachablePropagation {:?} ", body.source.def_id()))
+ {
+ return;
+ }
+
let mut unreachable_blocks = FxHashSet::default();
let mut replacements = FxHashMap::default();
From b4c94241476298936a868b1416f7285ab1e320a7 Mon Sep 17 00:00:00 2001
From: cjkenn <cjkenn@users.noreply.github.com>
Date: Mon, 16 Nov 2020 19:02:02 -0500
Subject: [PATCH 2/7] update ui test for increased fuel usage
---
src/test/ui/print-fuel/print-fuel.stderr | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/test/ui/print-fuel/print-fuel.stderr b/src/test/ui/print-fuel/print-fuel.stderr
index cc88cc077bb21..f1424d587d0d2 100644
--- a/src/test/ui/print-fuel/print-fuel.stderr
+++ b/src/test/ui/print-fuel/print-fuel.stderr
@@ -1 +1 @@
-Fuel used by foo: 3
+Fuel used by foo: 7
From 51c2218d1feb38272963ea39768996eb81a13826 Mon Sep 17 00:00:00 2001
From: cjkenn <cjkenn@users.noreply.github.com>
Date: Wed, 18 Nov 2020 08:49:46 -0500
Subject: [PATCH 3/7] move fuel checks to later points in instcombine and
const_prop, add opt level flag to test
---
.../rustc_mir/src/transform/const_prop.rs | 10 +++---
.../rustc_mir/src/transform/instcombine.rs | 35 +++++++++++--------
src/test/ui/print-fuel/print-fuel.rs | 2 +-
src/test/ui/print-fuel/print-fuel.stderr | 2 +-
4 files changed, 28 insertions(+), 21 deletions(-)
diff --git a/compiler/rustc_mir/src/transform/const_prop.rs b/compiler/rustc_mir/src/transform/const_prop.rs
index 1f266a95f03f6..abcf1862fd873 100644
--- a/compiler/rustc_mir/src/transform/const_prop.rs
+++ b/compiler/rustc_mir/src/transform/const_prop.rs
@@ -89,10 +89,6 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
return;
}
- if !tcx.consider_optimizing(|| format!("ConstantPropagation {:?} {:?}", def_id, hir_id)) {
- return;
- }
-
// Check if it's even possible to satisfy the 'where' clauses
// for this item.
// This branch will never be taken for any normal function.
@@ -804,7 +800,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
}
}
- trace!("attepting to replace {:?} with {:?}", rval, value);
+ trace!("attempting to replace {:?} with {:?}", rval, value);
if let Err(e) = self.ecx.const_validate_operand(
value,
vec![],
@@ -894,6 +890,10 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
return false;
}
+ if !self.tcx.consider_optimizing(|| format!("ConstantPropagation - OpTy: {:?}", op)) {
+ return false;
+ }
+
match *op {
interpret::Operand::Immediate(Immediate::Scalar(ScalarMaybeUninit::Scalar(s))) => {
s.is_bits()
diff --git a/compiler/rustc_mir/src/transform/instcombine.rs b/compiler/rustc_mir/src/transform/instcombine.rs
index 5a21cdc6891f4..3eb2b500d6627 100644
--- a/compiler/rustc_mir/src/transform/instcombine.rs
+++ b/compiler/rustc_mir/src/transform/instcombine.rs
@@ -20,13 +20,6 @@ pub struct InstCombine;
impl<'tcx> MirPass<'tcx> for InstCombine {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
- // Check for fuel here before gathering the optimization list. If we're out of fuel,
- // we don't want to take the time to pass over the MIR only to find optimizations
- // we won't run.
- if !tcx.consider_optimizing(|| format!("InstCombine {:?} ", body.source.def_id())) {
- return;
- }
-
// First, find optimization opportunities. This is done in a pre-pass to keep the MIR
// read-only so that we can do global analyses on the MIR in the process (e.g.
// `Place::ty()`).
@@ -46,13 +39,21 @@ pub struct InstCombineVisitor<'tcx> {
tcx: TyCtxt<'tcx>,
}
+impl<'tcx> InstCombineVisitor<'tcx> {
+ fn should_combine(&self, rvalue: &Rvalue<'tcx>, location: Location) -> bool {
+ self.tcx.consider_optimizing(|| {
+ format!("InstCombine - Rvalue: {:?} Location: {:?}", rvalue, location)
+ })
+ }
+}
+
impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
fn tcx(&self) -> TyCtxt<'tcx> {
self.tcx
}
fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
- if self.optimizations.and_stars.remove(&location) {
+ if self.optimizations.and_stars.remove(&location) && self.should_combine(rvalue, location) {
debug!("replacing `&*`: {:?}", rvalue);
let new_place = match rvalue {
Rvalue::Ref(_, _, place) => {
@@ -74,18 +75,24 @@ impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
}
if let Some(constant) = self.optimizations.arrays_lengths.remove(&location) {
- debug!("replacing `Len([_; N])`: {:?}", rvalue);
- *rvalue = Rvalue::Use(Operand::Constant(box constant));
+ if self.should_combine(rvalue, location) {
+ debug!("replacing `Len([_; N])`: {:?}", rvalue);
+ *rvalue = Rvalue::Use(Operand::Constant(box constant));
+ }
}
if let Some(operand) = self.optimizations.unneeded_equality_comparison.remove(&location) {
- debug!("replacing {:?} with {:?}", rvalue, operand);
- *rvalue = Rvalue::Use(operand);
+ if self.should_combine(rvalue, location) {
+ debug!("replacing {:?} with {:?}", rvalue, operand);
+ *rvalue = Rvalue::Use(operand);
+ }
}
if let Some(place) = self.optimizations.unneeded_deref.remove(&location) {
- debug!("unneeded_deref: replacing {:?} with {:?}", rvalue, place);
- *rvalue = Rvalue::Use(Operand::Copy(place));
+ if self.should_combine(rvalue, location) {
+ debug!("unneeded_deref: replacing {:?} with {:?}", rvalue, place);
+ *rvalue = Rvalue::Use(Operand::Copy(place));
+ }
}
self.super_rvalue(rvalue, location)
diff --git a/src/test/ui/print-fuel/print-fuel.rs b/src/test/ui/print-fuel/print-fuel.rs
index e443469544617..c7d49b5874436 100644
--- a/src/test/ui/print-fuel/print-fuel.rs
+++ b/src/test/ui/print-fuel/print-fuel.rs
@@ -2,7 +2,7 @@
#![allow(dead_code)]
// (#55495: The --error-format is to sidestep an issue in our test harness)
-// compile-flags: --error-format human -Z print-fuel=foo
+// compile-flags: -C opt-level=0 --error-format human -Z print-fuel=foo
// build-pass (FIXME(62277): could be check-pass?)
struct S1(u8, u16, u8);
diff --git a/src/test/ui/print-fuel/print-fuel.stderr b/src/test/ui/print-fuel/print-fuel.stderr
index f1424d587d0d2..e8ed746f57f0d 100644
--- a/src/test/ui/print-fuel/print-fuel.stderr
+++ b/src/test/ui/print-fuel/print-fuel.stderr
@@ -1 +1 @@
-Fuel used by foo: 7
+Fuel used by foo: 6
From 1e524fb36c0d1d20495b67ccb232f123d7a11891 Mon Sep 17 00:00:00 2001
From: cjkenn <cjkenn@users.noreply.github.com>
Date: Wed, 18 Nov 2020 11:27:37 -0500
Subject: [PATCH 4/7] change print-fuel ui test to check-pass
---
src/test/ui/print-fuel/print-fuel.rs | 2 +-
src/test/ui/print-fuel/print-fuel.stderr | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/test/ui/print-fuel/print-fuel.rs b/src/test/ui/print-fuel/print-fuel.rs
index c7d49b5874436..f68de00b9b591 100644
--- a/src/test/ui/print-fuel/print-fuel.rs
+++ b/src/test/ui/print-fuel/print-fuel.rs
@@ -3,7 +3,7 @@
// (#55495: The --error-format is to sidestep an issue in our test harness)
// compile-flags: -C opt-level=0 --error-format human -Z print-fuel=foo
-// build-pass (FIXME(62277): could be check-pass?)
+// check-pass
struct S1(u8, u16, u8);
struct S2(u8, u16, u8);
diff --git a/src/test/ui/print-fuel/print-fuel.stderr b/src/test/ui/print-fuel/print-fuel.stderr
index e8ed746f57f0d..4cbda0d8b2514 100644
--- a/src/test/ui/print-fuel/print-fuel.stderr
+++ b/src/test/ui/print-fuel/print-fuel.stderr
@@ -1 +1 @@
-Fuel used by foo: 6
+Fuel used by foo: 4
From b556690c53d87ea7530c631d3c257da3567e5a9a Mon Sep 17 00:00:00 2001
From: cjkenn <cjkenn@users.noreply.github.com>
Date: Wed, 18 Nov 2020 19:16:23 -0500
Subject: [PATCH 5/7] move checks later into optimization passes
---
.../src/transform/multiple_return_terminators.rs | 11 +++++------
.../rustc_mir/src/transform/remove_unneeded_drops.rs | 10 ++++++----
compiler/rustc_mir/src/transform/unreachable_prop.rs | 12 ++++++------
3 files changed, 17 insertions(+), 16 deletions(-)
diff --git a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
index 4a66bc45ae37b..617086622cc1a 100644
--- a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
+++ b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
@@ -14,14 +14,9 @@ impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
return;
}
- if !tcx.consider_optimizing(|| {
- format!("MultipleReturnTerminators {:?} ", body.source.def_id())
- }) {
- return;
- }
-
// find basic blocks with no statement and a return terminator
let mut bbs_simple_returns = BitSet::new_empty(body.basic_blocks().len());
+ let def_id = body.source.def_id();
let bbs = body.basic_blocks_mut();
for idx in bbs.indices() {
if bbs[idx].statements.is_empty()
@@ -32,6 +27,10 @@ impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
}
for bb in bbs {
+ if !tcx.consider_optimizing(|| format!("MultipleReturnTerminators {:?} ", def_id)) {
+ break;
+ }
+
if let TerminatorKind::Goto { target } = bb.terminator().kind {
if bbs_simple_returns.contains(target) {
bb.terminator_mut().kind = TerminatorKind::Return;
diff --git a/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
index 2a72751071bb1..221114eebaa45 100644
--- a/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
+++ b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
@@ -11,10 +11,6 @@ pub struct RemoveUnneededDrops;
impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
- if !tcx.consider_optimizing(|| format!("RemoveUnneededDrops {:?} ", body.source.def_id())) {
- return;
- }
-
trace!("Running RemoveUnneededDrops on {:?}", body.source);
let mut opt_finder = RemoveUnneededDropsOptimizationFinder {
tcx,
@@ -25,6 +21,12 @@ impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
opt_finder.visit_body(body);
let should_simplify = !opt_finder.optimizations.is_empty();
for (loc, target) in opt_finder.optimizations {
+ if !tcx
+ .consider_optimizing(|| format!("RemoveUnneededDrops {:?} ", body.source.def_id()))
+ {
+ break;
+ }
+
let terminator = body.basic_blocks_mut()[loc.block].terminator_mut();
debug!("SUCCESS: replacing `drop` with goto({:?})", target);
terminator.kind = TerminatorKind::Goto { target };
diff --git a/compiler/rustc_mir/src/transform/unreachable_prop.rs b/compiler/rustc_mir/src/transform/unreachable_prop.rs
index 4100a50c225b3..e39c8656021b2 100644
--- a/compiler/rustc_mir/src/transform/unreachable_prop.rs
+++ b/compiler/rustc_mir/src/transform/unreachable_prop.rs
@@ -18,12 +18,6 @@ impl MirPass<'_> for UnreachablePropagation {
return;
}
- if !tcx
- .consider_optimizing(|| format!("UnreachablePropagation {:?} ", body.source.def_id()))
- {
- return;
- }
-
let mut unreachable_blocks = FxHashSet::default();
let mut replacements = FxHashMap::default();
@@ -56,6 +50,12 @@ impl MirPass<'_> for UnreachablePropagation {
let replaced = !replacements.is_empty();
for (bb, terminator_kind) in replacements {
+ if !tcx.consider_optimizing(|| {
+ format!("UnreachablePropagation {:?} ", body.source.def_id())
+ }) {
+ break;
+ }
+
body.basic_blocks_mut()[bb].terminator_mut().kind = terminator_kind;
}
From 1d3305aa6668705af71aaab82a004c5c06642246 Mon Sep 17 00:00:00 2001
From: cjkenn <cjkenn@users.noreply.github.com>
Date: Thu, 19 Nov 2020 08:21:20 -0500
Subject: [PATCH 6/7] remove check from const promotion
---
compiler/rustc_mir/src/transform/promote_consts.rs | 4 ----
1 file changed, 4 deletions(-)
diff --git a/compiler/rustc_mir/src/transform/promote_consts.rs b/compiler/rustc_mir/src/transform/promote_consts.rs
index 0539d8fffabc8..927aae82a36ef 100644
--- a/compiler/rustc_mir/src/transform/promote_consts.rs
+++ b/compiler/rustc_mir/src/transform/promote_consts.rs
@@ -60,10 +60,6 @@ impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> {
return;
}
- if !tcx.consider_optimizing(|| format!("PromoteTemps {:?} ", body.source.def_id())) {
- return;
- }
-
let mut rpo = traversal::reverse_postorder(body);
let ccx = ConstCx::new(tcx, body);
let (temps, all_candidates) = collect_temps_and_candidates(&ccx, &mut rpo);
From 07de70250bd350befde0bf80fcb0e2836cd5d8b9 Mon Sep 17 00:00:00 2001
From: cjkenn <cjkenn@users.noreply.github.com>
Date: Thu, 19 Nov 2020 08:47:00 -0500
Subject: [PATCH 7/7] update print fuel test output again...
---
src/test/ui/print-fuel/print-fuel.stderr | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/test/ui/print-fuel/print-fuel.stderr b/src/test/ui/print-fuel/print-fuel.stderr
index 4cbda0d8b2514..cc88cc077bb21 100644
--- a/src/test/ui/print-fuel/print-fuel.stderr
+++ b/src/test/ui/print-fuel/print-fuel.stderr
@@ -1 +1 @@
-Fuel used by foo: 4
+Fuel used by foo: 3