bjoernager/rust
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Remove stack_store without following stack_load

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This commit is contained in:
bjorn3 2019-12-28 17:51:22 +01:00
parent 6320c65484
commit df7f68236c
1 changed files with 32 additions and 15 deletions
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47
src/optimize/stack2reg.rs
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@ -76,11 +76,9 @@ pub(super) fn optimize_function(
// FIXME Repeat following instructions until fixpoint.
println!("{}:\nstack slot usage: {:?}", name, stack_slot_usage_map);
remove_unused_stack_addr_and_stack_load(&mut ctx.func, &mut stack_slot_usage_map);
println!("stack slot usage (after): {:?}", stack_slot_usage_map);
println!("stack slot usage: {:?}", stack_slot_usage_map);
for (stack_slot, users) in stack_slot_usage_map.iter_mut() {
if users.stack_addr.is_empty().not() {
@ -95,8 +93,6 @@ pub(super) fn optimize_function(
let loaded_type = ctx.func.dfg.value_type(loaded_value);
let potential_stores = users.stack_store.iter().cloned().filter(|&store| {
// Check if the store modified some memory accessed by the load.
match spatial_overlap(&ctx.func, load, store) {
SpatialOverlap::No => false, // Can never be the source of the loaded value.
SpatialOverlap::Partial | SpatialOverlap::Full => true,
@ -107,6 +103,7 @@ pub(super) fn optimize_function(
TemporalOrder::MaybeBefore | TemporalOrder::DefinitivelyBefore => true,
}
}).collect::<Vec<Inst>>();
for &store in &potential_stores {
println!(
"Potential store -> load forwarding {} -> {} ({:?}, {:?})",
@ -120,6 +117,7 @@ pub(super) fn optimize_function(
match *potential_stores {
[] => println!("[{}] [BUG?] Reading uninitialized memory", name),
[store] if spatial_overlap(&ctx.func, store, load) == SpatialOverlap::Full && temporal_order(&ctx, store, load) == TemporalOrder::DefinitivelyBefore => {
// Only one store could have been the origin of the value.
let store_ebb = ctx.func.layout.inst_ebb(store).unwrap();
let stored_value = ctx.func.dfg.inst_args(store)[0];
let stored_type = ctx.func.dfg.value_type(stored_value);
@ -135,12 +133,35 @@ pub(super) fn optimize_function(
}
}
if users.stack_load.is_empty() {
// Never loaded; can safely remove all stores and the stack slot.
// FIXME also remove stores when there is always a next store before a load.
for user in users.stack_store.drain() {
println!("[{}] Remove dead stack store {} of {}", name, user, stack_slot.0);
ctx.func.dfg.replace(user).nop();
for store in users.stack_store.clone().drain() {
let potential_loads = users.stack_load.iter().cloned().filter(|&load| {
match spatial_overlap(&ctx.func, store, load) {
SpatialOverlap::No => false, // Can never be the source of the loaded value.
SpatialOverlap::Partial | SpatialOverlap::Full => true,
}
}).filter(|&load| {
match temporal_order(&*ctx, store, load) {
TemporalOrder::NeverBefore => false, // Can never be the source of the loaded value.
TemporalOrder::MaybeBefore | TemporalOrder::DefinitivelyBefore => true,
}
}).collect::<Vec<Inst>>();
for &load in &potential_loads {
println!(
"Potential load from store {} <- {} ({:?}, {:?})",
ctx.func.dfg.display_inst(load, None),
ctx.func.dfg.display_inst(store, None),
spatial_overlap(&ctx.func, store, load),
temporal_order(&*ctx, store, load),
);
}
if potential_loads.is_empty() {
// Never loaded; can safely remove all stores and the stack slot.
// FIXME also remove stores when there is always a next store before a load.
println!("[{}] Remove dead stack store {} of {}", name, ctx.func.dfg.display_inst(store, None), stack_slot.0);
ctx.func.dfg.replace(store).nop();
users.stack_store.remove(&store);
}
}
@ -205,8 +226,6 @@ fn remove_unused_stack_addr_and_stack_load(func: &mut Function, stack_slot_usage
}
}
println!("stack_addr/stack_load users: {:?}", stack_addr_load_insts_users);
for inst in stack_addr_load_insts_users.keys() {
let mut is_recorded_stack_addr_or_stack_load = false;
for stack_slot_users in stack_slot_usage_map.values() {
@ -220,7 +239,6 @@ fn remove_unused_stack_addr_and_stack_load(func: &mut Function, stack_slot_usage
// FIXME remove clone
for &inst in stack_slot_users.stack_addr.clone().iter() {
if stack_addr_load_insts_users.get(&inst).map(|users| users.is_empty()).unwrap_or(true) {
println!("Removing unused stack_addr {}", inst);
func.dfg.detach_results(inst);
func.dfg.replace(inst).nop();
stack_slot_users.stack_addr.remove(&inst);
@ -229,7 +247,6 @@ fn remove_unused_stack_addr_and_stack_load(func: &mut Function, stack_slot_usage
for &inst in stack_slot_users.stack_load.clone().iter() {
if stack_addr_load_insts_users.get(&inst).map(|users| users.is_empty()).unwrap_or(true) {
println!("Removing unused stack_addr {}", inst);
func.dfg.detach_results(inst);
func.dfg.replace(inst).nop();
stack_slot_users.stack_load.remove(&inst);