[test] Add s390x support for test/IRGen/pic.swift

[levivic]

This is adding s390x support for test/IRGen/pic.swift.

[compnerd]

Hmm, I don't know s390 assembly to properly review this. Why does $s4main6globalSivp not need any modifiers for the PIC access?

[rjmccall]

Looks like lgrl takes a 32-bit relative offset.

It looks like this is hard-coding a specific frame layout. Are you okay with potentially changing this test whenever you change the backend?

[levivic]

Hmm, I don't know s390 assembly to properly review this. Why does $s4main6globalSivp not need any modifiers for the PIC access?

By reading the check label for other cpu (e.g., x86_64, aarch64) within this test file, I am not sure what kind of modifier $s4main6globalSivp needs. On s390x, lgrl load $s4main6globalSivp into REG2 and REG2 is stg stored into address REG4 +160.

[levivic]

Looks like lgrl takes a 32-bit relative offset.

It looks like this is hard-coding a specific frame layout. Are you okay with potentially changing this test whenever you change the backend?

You mean potentially change of this test whenever the backend platform is changed? If so, yes, our team has been closely following the development of swift, as well as the platform we are using.

[rjmccall]

I am not sure what kind of modifier $s4main6globalSivp needs.

@compnerd is just unfamiliar with z/Architecture assembly. In many assembly languages, the fact that the immediate is PC-relative would be more explicit.

You mean potentially change of this test whenever the backend platform is changed? If so, yes, our team has been closely following the development of swift, as well as the platform we are using.

It feels like an unnecessary burden to have frontend tests break from unrelated backend changes. If this test is just checking that we generate PIC, I think the only line you actually need here is the lgrl.

[levivic]

It feels like an unnecessary burden to have frontend tests break from unrelated backend changes. If this test is just checking that we generate PIC, I think the only line you actually need here is the lgrl.

Sure, will provide an update. Thanks.

[rjmccall]

Great, thanks!

[rjmccall]

@swift-ci Please test.

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 05fbe8d

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 05fbe8d