Struct Profile 

pub struct Profile {
    pub requested: bool,
    pub path: Option<String>,
    pub dir: Option<String>,
    pub absolute: bool,
    pub correction: bool,
    pub partial_training: bool,
}

What the profile reading half of the -fprofile family asked for.

A profile is a count per edge, gathered by running a build of the program that was instrumented to count, and read back on a second compilation so that the optimizer knows which way each branch actually went. It is worth more than any single optimization, because almost everything the optimizer decides is a guess about a frequency that the counts simply state.

Nothing here reads one yet, so this is recorded rather than acted on, and the family splits in two rather than being taken or refused as a whole. The half recorded here is the half that only costs speed when it is ignored: a build that asks to read a profile and is not read one gets the program it would have got anyway, which is what section 4.1 means by a hint about speed. The other half writes files, and that half is refused by the driver rather than landing here, on the same reading -gsplit-dwarf gets: a program instrumented by -fprofile-generate writes a .gcda when it runs and -ftest-coverage writes a .gcno beside the object, and ignoring either means a build waits for a file that never arrives and then quietly optimizes against no counts at all.

gcc’s own measurement is the argument for the split. -fprofile-use on a file with no counts beside it produces an object byte for byte identical to the one no flag produces, and warns; the same file under -fprofile-generate grows from 71 bytes of code to 375 with 296 bytes of counters beside it. So one half of the family is already a no-op in gcc when there is nothing to read, and the other half is never one.

Fields

requested: bool

Whether the last of -fprofile-use and -fno-profile-use on the command line was the first of the two.

path: Option<String>

Where to read the counts from, from -fprofile-use=<path>, where None means beside the object the way gcc looks when nobody says. A directory or a file, which is gcc’s rule and is not something this can tell apart without looking at the filesystem.

dir: Option<String>

Where the whole family’s files live, from -fprofile-dir=. Separate from path because gcc keeps them separate: this one moves the counts for the generating half as well.

absolute: bool

Whether the path recorded in those files is made absolute, from -fprofile-abs-path. It is what a build with several object directories under one source tree needs so that two files of the same name do not land on one set of counts.

correction: bool

Whether counts that do not add up are repaired rather than refused, from -fprofile-correction. A program that forked or was killed while it ran leaves counts that no single execution could have produced, and this says to make the best of them.

partial_training: bool

Whether the parts of the program the training run never reached are optimized as if they were cold rather than as if nothing were known about them, from -fprofile-partial-training.

Trait Implementations

impl Clone for Profile

fn clone(&self) -> Profile

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Profile

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

Formats the value using the given formatter.

impl Default for Profile

fn default() -> Profile

Returns the “default value” for a type.

impl Eq for Profile

impl PartialEq for Profile

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Profile