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Fat LTO objects contain both LTO compatible IR, as well as generated object code. This allows users to defer the choice of whether to use LTO or not to link-time. This is a feature available in GCC for some time, and makes the existing -ffat-lto-objects flag functional in the same way as GCC's. Within LLVM, we add a new EmbedBitcodePass that serializes the module to the object file, and expose a new pass pipeline for compiling fat objects. The new pipeline initially clones the module and runs the selected (Thin)LTOPrelink pipeline, after which it will serialize the module into a `.llvm.lto` section of an ELF file. When compiling for (Thin)LTO, this normally the point at which the compiler would emit a object file containing the bitcode and metadata. After that point we compile the original module using the PerModuleDefaultPipeline used for non-LTO compilation. We generate standard object files at the end of this pipeline, which contain machine code and the new `.llvm.lto` section containing bitcode. Since the two pipelines operate on different copies of the module, we can be sure that the bitcode in the `.llvm.lto` section and object code in `.text` are congruent with the existing output produced by the default and LTO pipelines. Original RFC: https://discourse.llvm.org/t/rfc-ffat-lto-objects-support/63977 Earlier versions of this patch were missing REQUIRES lines for llc related tests in Transforms/EmbedBitcode. Those tests are now under CodeGen/X86, which should avoid running the check on unsupported platforms. The EmbedbBitcodePass also returned PreservedAnalyses::all when adding a metadata section, which failed expensive checks, since it modified the module. This is now corrected. Reviewed By: tejohnson, MaskRay, nikic Differential Revision: https://reviews.llvm.org/D146776
6 lines
198 B
LLVM
6 lines
198 B
LLVM
; RUN: not opt --mtriple powerpc64-unknown-aix < %s -passes=embed-bitcode -S 2>&1 | FileCheck %s
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@a = global i32 1
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; CHECK: LLVM ERROR: EmbedBitcode pass currently only supports ELF object format
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