Enum OptLevel 

pub enum OptLevel {
    O0,
    O1,
    O2,
    O3,
    Os,
    Oz,
}

An optimisation level.

spec/16-performance.md section 16.4 gives each level a throughput budget and a code quality budget, and the levels exist to make that tradeoff explicit rather than to be a dial. There is no -O4, because a level nobody can state the contract for is a level nobody can test.

Variants

O0

-O0. Compile as fast as possible and keep every variable inspectable.

O1

-O1. The cheap wins, at roughly the cost of -O0.

O2

-O2. The full pipeline. This is the level the code quality claim is about.

O3

-O3. -O2 plus the transformations that trade size for speed.

Os

-Os. Optimise for size, at roughly -O2 compile time.

Oz

-Oz. Optimise for size, aggressively.

Implementations

impl OptLevel

pub const fn as_flag(self) -> &'static str

The flag that selects this level.

pub const fn is_size(self) -> bool

Whether this level optimises for size rather than speed.

pub const fn runs_optimizer(self) -> bool

Whether the middle end runs at all.

pub const fn schedules(self) -> bool

Whether the instructions of a block are put in the order the machine finishes soonest.

spec/optimizer/38-scheduling-and-layout.md section 38.6 says -O2 and above, and gcc turns -fschedule-insns2 on at the two size levels as well, which costs nothing: a schedule is a permutation of instructions that were all going to be written anyway, so it is the one optimization here that cannot make a function larger.

Trait Implementations

impl Clone for OptLevel

fn clone(&self) -> OptLevel

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for OptLevel

impl Debug for OptLevel

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for OptLevel

fn default() -> OptLevel

Returns the “default value” for a type.

impl Display for OptLevel

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for OptLevel

impl FromStr for OptLevel

fn from_str(s: &str) -> Result<Self, ()>

Parses the part after -O, so "" is -O which GCC treats as -O1.

type Err = ()

The associated error which can be returned from parsing.

impl Hash for OptLevel

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for OptLevel

fn cmp(&self, other: &OptLevel) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for OptLevel

fn eq(&self, other: &OptLevel) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl PartialOrd for OptLevel

fn partial_cmp(&self, other: &OptLevel) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for OptLevel