LLVM and Clang wanted features & bugfixes

[ojeda]

Features that we would like to see

Required (we almost certainly want them)

• If a new approach for kCFI type IDs is introduced, then a way to query/set the kind being used is needed.
  • The mechanism used in both rustc and Clang need to agree, thus we need to ensure they are the same.
  • If a single approach is supported (rather than supporting several at the same time), then it may be hard to mix and match rustc/Clang versions.
  • PR (introducing a new approach): [X86] Enhance kCFI type IDs with a 3-bit arity indicator. llvm/llvm-project#117121.
  • PR (another approach): [X86] Extend kCFI with a 3-bit arity indicator llvm/llvm-project#121070.

Nice to have (not critical, we could workaround if needed, etc.)

Low priority (we will likely not use them in the end)

Done (stabilized, fixed, not needed anymore, etc.)

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Bugs that we would like to see fixed

Required (we almost certainly want them)

Nice to have (probably not critical, we could workaround if needed, etc.)

Low priority (we will likely not use them in the end)

Done (stabilized, fixed, or not needed anymore, etc.)

• LLVM miscompilation for asm goto with outputs.
  • Issue: asm goto miscompilation llvm/llvm-project#74483.
  • Issue: asm goto wrong output at -O0 llvm/llvm-project#110251.
  • PR: [RegAllocFast] Ensure live-in vregs get reloaded after INLINEASM_BR spills llvm/llvm-project#131350 (21?).