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clarify MIR uninit vs LLVM undef/poison

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This commit is contained in:
Ralf Jung 2023-07-20 18:40:15 +02:00
parent 77e24f90f5
commit 41a73d8251
2 changed files with 7 additions and 1 deletions
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6
compiler/rustc_codegen_ssa/src/traits/consts.rs
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@ -5,7 +5,13 @@ use rustc_target::abi;
pub trait ConstMethods<'tcx>: BackendTypes {
// Constant constructors
fn const_null(&self, t: Self::Type) -> Self::Value;
/// Generate an uninitialized value (matching uninitialized memory in MIR).
/// Whether memory is initialized or not is tracked byte-for-byte.
fn const_undef(&self, t: Self::Type) -> Self::Value;
/// Generate a fake value. Poison always affects the entire value, even if just a single byte is
/// poison. This can only be used in codepaths that are already UB, i.e., UB-free Rust code
/// (including code that e.g. copies uninit memory with `MaybeUninit`) can never encounter a
/// poison value.
fn const_poison(&self, t: Self::Type) -> Self::Value;
fn const_int(&self, t: Self::Type, i: i64) -> Self::Value;
fn const_uint(&self, t: Self::Type, i: u64) -> Self::Value;