llvm-lto2: Add print-guid subcommand.

[pcc]

This is useful for debugging ThinLTO issues.

[teresajohnson]

This needs a caveat somewhere (either in printed usage message or in a comment) that this won't work for local linkage symbols (I suppose the user could give the "file:" prefix but that won't work if -funique-internal-linkage-names was specified etc). Can you also add a test?

[pcc]

This needs a caveat somewhere (either in printed usage message or in a comment) that this won't work for local linkage symbols (I suppose the user could give the "file:" prefix but that won't work if -funique-internal-linkage-names was specified etc).

I'm not sure that is worth it. The intent is that users of these development tools will refer to the source code. And if you read the source code you'll see the function name getGUIDAssumingExternalLinkage which tells you what you need to know.

Can you also add a test?

Done.

[teresajohnson]

This needs a caveat somewhere (either in printed usage message or in a comment) that this won't work for local linkage symbols (I suppose the user could give the "file:" prefix but that won't work if -funique-internal-linkage-names was specified etc).

I'm not sure that is worth it. The intent is that users of these development tools will refer to the source code. And if you read the source code you'll see the function name getGUIDAssumingExternalLinkage which tells you what you need to know.

At least a comment in the code would be good. A variety of people end up using these tools for tests, and I could see someone getting confused as to why the guid doesn't match what's e.g. in the ThinLTO index. For that understanding you'd have to read more than just what this source file is calling.

[teresajohnson]

lgtm otherwise

[pcc]

At least a comment in the code would be good. A variety of people end up using these tools for tests, and I could see someone getting confused as to why the guid doesn't match what's e.g. in the ThinLTO index. For that understanding you'd have to read more than just what this source file is calling.

I added a comment.