Sometimes MIR-level passes create DILocations that were not present in the
LLVM-IR. For example, it may merge two DILocations together to produce a
DILocation that points to line 0.
Previously, the address of these DILocations were printed which prevented the
MIR from being read back into LLVM. With this patch, DILocations will use
metadata references where possible and fall back on serializing them inline like so:
MOV32mr %stack.0.x.addr, 1, _, 0, _, %0, debug-location !DILocation(line: 1, scope: !15)