llvm dev - Nov 2018 - How to handle use of attribute group IDs with missing attribute group definition?

Hi,

We've been exploring the test case suite of LLVM recently, and came across
quite a few test cases that reference attribute group IDs (e.g. `#2`), not
being defined in the module (i..e no associate attribute group definition
`#2 = {}`).

For instance, test/DebugInfo/X86/parameters.ll [1] uses #0, #1 and #2, but
only contains definitions for #0 and #1. The definition for #2 is missing.

So, my question is, is this valid LLVM IR? I tried to run the file through
opt -verify, but no error or warning was reported.

If it is valid LLVM IR, what is the behaviour when parsing such files? To
insert an empty definition (i.e. `#2 = {}`), or to remove uses of undefined
attribute group definitions (i.e. remove any reference of #2)?

Kindly,
Robin


[1]:
https://github.com/llvm-mirror/llvm/blob/master/test/DebugInfo/X86/parameters.ll
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