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Avoid allocating a vector for predecessor variables in the single-value case.

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This commit is contained in:
Dan Gohman
2017-08-31 17:42:19 -07:00
parent 52335c9e0f
commit ec3972f515
1 changed files with 18 additions and 19 deletions
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37
lib/frontend/src/ssa.rs
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@@ -161,7 +161,7 @@ where
enum ZeroOneOrMore<T> {
Zero(),
One(T),
More(),
More(Vec<T>),
}
#[derive(Debug)]
@@ -409,9 +409,7 @@ where
temp_arg_var: Variable,
dest_ebb: Ebb,
) -> (Value, SideEffects) {
let mut pred_values: ZeroOneOrMore<Value> = ZeroOneOrMore::Zero();
// TODO: find a way to not allocate a vector
let mut jump_args_to_append: Vec<(Block, Inst, Value)> = Vec::new();
let mut pred_values: ZeroOneOrMore<(Block, Inst, Value)> = ZeroOneOrMore::Zero();
let ty = dfg.value_type(temp_arg_val);
let mut side_effects = SideEffects::new();
@@ -425,24 +423,25 @@ where
// to var and we put it as an argument of the branch instruction.
let (pred_val, mut local_side_effects) =
self.use_var(dfg, layout, jts, temp_arg_var, ty, pred);
pred_values = match pred_values {
match pred_values {
ZeroOneOrMore::Zero() => {
if pred_val == temp_arg_val {
ZeroOneOrMore::Zero()
} else {
ZeroOneOrMore::One(pred_val)
if pred_val != temp_arg_val {
pred_values = ZeroOneOrMore::One((pred, last_inst, pred_val))
}
}
ZeroOneOrMore::One(old_val) => {
if pred_val == temp_arg_val || pred_val == old_val {
ZeroOneOrMore::One(old_val)
} else {
ZeroOneOrMore::More()
ZeroOneOrMore::One((old_pred, old_last_inst, old_val)) => {
if pred_val != temp_arg_val && pred_val != old_val {
// TODO: find a way to not allocate a vector
pred_values = ZeroOneOrMore::More(vec![
(old_pred, old_last_inst, old_val),
(pred, last_inst, pred_val),
]);
}
}
ZeroOneOrMore::More() => ZeroOneOrMore::More(),
};
jump_args_to_append.push((pred, last_inst, pred_val));
ZeroOneOrMore::More(ref mut jump_args_to_append) => {
jump_args_to_append.push((pred, last_inst, pred_val));
}
}
side_effects.split_ebbs_created.append(
&mut local_side_effects
.split_ebbs_created,
@@ -479,7 +478,7 @@ where
side_effects.instructions_added_to_ebbs.push(dest_ebb);
(val, side_effects)
}
ZeroOneOrMore::One(pred_val) => {
ZeroOneOrMore::One((_, _, pred_val)) => {
// Here all the predecessors use a single value to represent our variable
// so we don't need to have it as an ebb argument.
// We need to replace all the occurences of val with pred_val but since
@@ -488,7 +487,7 @@ where
dfg.change_to_alias(temp_arg_val, pred_val);
(pred_val, side_effects)
}
ZeroOneOrMore::More() => {
ZeroOneOrMore::More(jump_args_to_append) => {
// There is disagreement in the predecessors on which value to use so we have
// to keep the ebb argument.
for (pred_block, last_inst, pred_val) in jump_args_to_append {