Maximum size of an array in 32 bits?

Question

According to the Rust Reference:

The isize type is a signed integer type with the same number of bits as the platform\'s pointer type. Th

Answer 1

Rust uses LLVM as compiler backend. The LLVM instruction for pointer arithmetic (GetElementPtr) takes signed integer offsets and has undefined behavior on overflow, so it is impossible to index into arrays larger than 2GB when targeting a 32-bit platform.

To avoid undefined behavior, Rust will refuse to allocate more than 2 GB in a single allocation. See Rust issue #18726 for details.