Struct Escapes 

pub struct Escapes { /* private fields */ }

Which of a function’s locals had their address leave it.

Section 8.4 calls this the most valuable interprocedural-flavoured fact available without interprocedural analysis, because it covers every local a C programmer takes the address of only to pass one field of, and because a local whose address never escaped cannot be touched by any call at all.

Section 8.6 says how it goes wrong, which is by missing an escape, and what to do about it. keeps_address is a whitelist: an opcode it does not name lets the address out, and so does an opcode added to the IR after this was written. A blacklist would mean the next person to add an opcode introduces a miscompilation without touching this file.

Implementations

impl Escapes

pub fn of(func: &Func) -> Self

Works out which locals of this function escaped it.

pub fn knowing(func: &Func, summaries: &Summaries) -> Self

The same, given what the functions this one calls do to what they are handed.

Section 34.6 calls this the upgrade the mod and ref summary makes possible: the question goes from does the address leave this function to does the address leave this function given what the callees do. An address handed to a call is an address gone as far as Escapes::of is concerned, and that is most of what a C program does with the address of a local, so a callee whose summary says it keeps nothing takes a whole class of locals out of the escaped set and every question about them afterwards is answered.

Note what this does to the reader of the answer. The invariant that a call reaching the escape layer of the oracle cannot have been handed the address does not hold any more, so that layer asks whether this call was handed it rather than assuming not.

pub fn with(func: &Func, kept: impl Fn(Inst, usize) -> bool) -> Self

The same, where kept says which operands of which calls hand the address to something that does not let it out. For crate::modref, whose own answers are still moving while it asks and which therefore cannot hand over a finished Summaries.

pub fn escaped(&self, local: Inst) -> bool

Whether the address of this alloca left the function.

pub fn count(&self) -> usize

How many locals escaped.

Trait Implementations

impl Clone for Escapes

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Escapes

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

Formats the value using the given formatter.

impl Default for Escapes

fn default() -> Self

Returns the “default value” for a type.