Use undef for (some) partially-uninit constants There needs to be some limit to avoid perf regressions on large arrays with undef in each element (see comment in the code). Fixes: #84565 Original PR: #83698 Depends on LLVM 14: #93577
The codegen
crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.