One of the goals of programming models that support offloading (e.g. OpenMP) is to enable users to offload with little effort, by annotating the code with a few pragmas. I'd also like to save users the trouble of changing their existent applications' build system. So having the compiler always return a single file instead of one for the host and each target even if the user is doing separate compilation is desirable.
This diff proposes a tool named clang-offload-bundler (happy to change the name if required) that is used to bundle files associated with the same user source file but different targets, or to unbundle a file into separate files associated with different targets.
This tool supports the driver support for OpenMP under review in http://reviews.llvm.org/D9888. The tool is used there to enable separate compilation, so that the very first action on input files that are not source files is a "unbundling action" and the very last non-linking action is a "bundling action".
The format of the bundled files is currently very simple: text formats are concatenated with comments that have a magic string and target identifying triple in between, and binary formats have a header that contains the triple and the offset and size of the code for host and each target.
The goal is to improve this tool in the future to deal with archive files so that each individual file in the archive is properly dealt with. We see that archives are very commonly used in current applications to combine separate compilation results. So I'm convinced users would enjoy this feature.
This tool can be used like this:
clang-offload-bundler -targets=triple1,triple2 -type=ii -inputs=a.triple1.ii,a.triple2.ii -outputs=a.ii
clang-offload-bundler -targets=triple1,triple2 -type=ii -outputs=a.triple1.ii,a.triple2.ii -inputs=a.ii -unbundle
I implemented the tool under clang/tools. Please let me know if something like this should live somewhere else.
This patch is prerequisite for http://reviews.llvm.org/D9888.