Struct Restrict 

pub struct Restrict {
    pub clique: u16,
    pub base: u16,
}

Which restrict scope an access is in, and which pointer inside that scope it went through.

Two small numbers, which is the whole of the mechanism. GCC spells them MR_DEPENDENCE_CLIQUE and MR_DEPENDENCE_BASE at gcc/tree-ssa-alias.cc:2503 and the rule is one line: same clique and different base means the two accesses cannot touch the same byte, because that is exactly what restrict promises. A clique is one scope, numbered as lowering enters it, and a base is one restrict pointer declared inside it. Clique zero means nothing is known, which is what every access that is not under a restrict gets.

This is spec 9.4’s scope tree rather than a blanket assumption, and it costs four bytes that were padding in MemInfo already.

Fields

clique: u16

The scope, with zero meaning no information.

base: u16

The pointer within that scope, which only means anything when the clique is not zero.

Implementations

impl Restrict

pub const NONE: Self

No information, which is what an access outside any restrict scope carries.

pub const fn disjoint(self, other: Self) -> bool

Whether restrict says these two accesses cannot touch the same byte.

Only accesses. GCC’s PR71062 is what happens when this answer is used to fold a comparison of the two pointers: restrict constrains what is read and written through a pointer and says nothing about what the pointer’s value is, so two pointers that may not be used to reach the same object can still compare equal. A rule that folds p == q to false on the strength of this is wrong.

Trait Implementations

impl Clone for Restrict

fn clone(&self) -> Restrict

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Restrict

impl Debug for Restrict

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

Formats the value using the given formatter.

impl Default for Restrict

fn default() -> Restrict

Returns the “default value” for a type.

impl Eq for Restrict

impl PartialEq for Restrict

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Restrict