Using DEBUG compilation slows down the compilation by nearly ~40 times.

Why ?
LLVM represents variable locations through DBG_VALUE records. Heavy function inlining can create hundreds of thousands of these records in a single function.

WebAssembly’s Register Stackify pass moves values from virtual registers onto the operand stack to produce compact, efficient wasm. While moving instructions, it repeatedly scans basic blocks to find and update debug records. Those linear scans are repeated for many definitions, while the pass also leaves invalidated records behind and creates new records for duplicated cheap computations. The result is quadratic work on increasingly large instruction lists.

As example:
Module: repro total codegen
Current Rust: 52.58s
LLM fix:7.12s
Author fix: 1.99s