[HIP] Support offloading by linker script

[yaxunl]

Summary

To support linking device code in different source files, it is necessary to
embed fat binary at host linking stage.

This patch emits an external symbol for fat binary in host codegen, then
embed the fat binary by lld through a linker script.

[rjmccall]

The IRGen aspects of this seem reasonable, modulo a comment change. I don't feel qualified to judge the driver change.

lib/CodeGen/CGCUDANV.cpp

317

Is this filename string only used for CUDA? If so, please rename it to make that clear, or at least add a comment.

[yaxunl]

lib/CodeGen/CGCUDANV.cpp

317

Yes. Will do.

[yaxunl]

Rename variables used for CUDA only.

[yaxunl]

ping

[t-tye]

LGTM except for minor suggestions.

lib/CodeGen/CGCUDANV.cpp

361–373

Should this all be inside an if (IsHip) so the names can be different for HIP and NV CUDA? Seems HIP should not be using names with VV_CUDA in them. In fact maybe the following IF should be included as well to consilidate the NV CUDA code and HIP code together.

394–398

Should HIP use the same magic value and version number? Perhaps this should also be moved into the IsHip IF.

438

Update comment for HIP

lib/Driver/ToolChains/CommonArgs.cpp

150

OpenMP -> OpenMP or HIP

1321–1322

for for -> for

[yaxunl]

In D46472#1103577, @t-tye wrote:

LGTM except for minor suggestions.

Thanks. Will make changes when committing.

[tra]

cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp

1371–1388 ↗

(On Diff #147511)

Using this linker script may present a problem.

INSERT BEFORE is not going to work with ld.gold.
https://sourceware.org/bugzilla/show_bug.cgi?id=15373

LLD also does not handle it particularly well -- INSERT BEFORE can only be used to override explicitly specified external linker script and virtually nobody uses linker scripts with LLD.
See tests in https://reviews.llvm.org/D44380

[pcc]

cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp

1371–1388 ↗

(On Diff #147511)

If you're just trying to embed a file it may be better to use MC to write an ELF with something like:

.section .hip_fatbin
.align 16
.globl __hip_fatbin
__hip_fatbin:
.incbin "BundleFileName"

and add that to the link.

[yaxunl]

cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp

1371–1388 ↗

(On Diff #147511)

In https://reviews.llvm.org/D45212 we specified to use lld for linking. Since this is an explicit linker script, it works. We have tested this approach with many HIP applications that it works well.

Similar approach has also been used by OpenMP for embedding device binary.

1371–1388 ↗

(On Diff #147511)

Thanks for your suggestion. We will consider using MC if we see issues arise due to linker script.

[JonChesterfield]

cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp

1329 ↗

(On Diff #147511)

Should this be toolchains::HipToolChain?

[yaxunl]

cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp

1329 ↗

(On Diff #147511)

will fix. thanks