[llvm] [DebugInfo] Make DIArgList inherit from Metadata and always unique (PR #72147)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Digging into this now, thanks for making this adjustment. Two high level concerns:
 * It looks like some files might end up being different according to the compile time tracker [0], in that one or two of the bitcode files report file-size differences. It's not clear to me whether that's actually a spurious difference though, as the numeric sizes aren't different.
 *  IIRC the reason why https://reviews.llvm.org/D108968 was filed was because of a nondeterminism problem when uniquifying DIArgLists that only appears deep in LTO builds. We should be careful about re-enabling DIArgList uniquification in light of that, I see it's being re-implemented here (will look), is that likely to solve the reported nondeterminism issue?

[0] http://llvm-compile-time-tracker.com/compare.php?from=9e618e5ed4c9f2c24e2c308e7f28e505e788f5fa&to=9552698bada4e3809331d57c0a78627161767ae6&stat=size-file&details=on

https://github.com/llvm/llvm-project/pull/72147