[PATCH] D14623: [ThinLTO] Comdat importing fixes and related cleanup

[Teresa Johnson via llvm-commits]

On Mon, Nov 30, 2015 at 11:29 AM, Rafael Espíndola
<rafael.espindola at gmail.com> wrote:
>> Do you mean if the imported function (say 'foo') references an alias ('f'),
>> the aliasee 'f2' will have to be imported and converted to internal linkage?
>
> Depends on what you want to import. My understanding is that your testcase is

Thinking some more about this:

>
> @f = alias void (), void ()* @f2
> define void @foo() {
>   call void @f()
>   ret void
> }
> define void @f2() {
>   ret void
> }
>
> if you want foo, f, f2, the output is like the input

Not exactly, f2 can't be imported as-is since that would result in
multiply-defined f2. To avoid that, f2() is imported as
available_externally. Unfortunately, with the change you made in
r254170 we cannot import f() as an alias of the imported f2. It needs
to be a declaration. That may be an issue if f and f2 are part of a
comdat, where we decided to select and therefore import the source
comdat group - it will be incomplete.

>
> if you want just foo, you get
>
> define void @foo() {
>   call void @f()
>   ret void
> |
> declare void @f()

This is what happens currently (with or without this patch), assuming
f() is not in a comdat group.

>
> if you want just foo and f, you get
>
> @f = alias void(), void()* @f2
> define void @foo() {
>   call void @f()
>   ret void
> }
> define internal void @f2() {
>   ret void
> }

Seems like I might need to do this conversion of f2 to internal
(instead of importing as available_externally) when it has an alias
and is part of a comdat group, to avoid an incomplete comdat group as
noted above?

Teresa

>
> take a look at pr19848 for another example.
>
> Cheers,
> Rafael



-- 
Teresa Johnson | Software Engineer | tejohnson at google.com | 408-460-2413