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Add comment with reasoning for non-determinism

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Smitty 2021-06-19 10:49:06 -04:00
parent a59fafeb13
commit ab66c3fbd4
1 changed files with 9 additions and 0 deletions
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9
compiler/rustc_middle/src/mir/interpret/allocation.rs
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@ -127,6 +127,15 @@ impl<Tag> Allocation<Tag> {
pub fn uninit(size: Size, align: Align) -> InterpResult<'static, Self> { pub fn uninit(size: Size, align: Align) -> InterpResult<'static, Self> {
let mut bytes = Vec::new(); let mut bytes = Vec::new();
bytes.try_reserve(size.bytes_usize()).map_err(|_| { bytes.try_reserve(size.bytes_usize()).map_err(|_| {
// This results in an error that can happen non-deterministically, since the memory
// available to the compiler can change between runs. Normally queries are always
// deterministic. However, we can be non-determinstic here because all uses of const
// evaluation do one of:
// - cause a fatal compiler error when they see this error as the result of const
// evaluation
// - panic on evaluation failure
// - always evaluate very small constants that are practically unlikely to result in
// memory exhaustion
InterpError::ResourceExhaustion(ResourceExhaustionInfo::MemoryExhausted) InterpError::ResourceExhaustion(ResourceExhaustionInfo::MemoryExhausted)
})?; })?;
bytes.resize(size.bytes_usize(), 0); bytes.resize(size.bytes_usize(), 0);