How to use LLVM-test-suite to experiment with alias analysis?

Beginners
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I guess you mean producing a single .bc file for the entire project comprises of potentially thousands of C/C++ files. If that’s the case you definitely need to use LTO (Link-Time Optimization) to produce that kind of “merged” bitcode file. (Theoretically you can use llvm-link but my experiences showed that that tool didn’t scale up really well)
Here are the steps:

  1. First, add the following compiler flag: -flto. In the case of CMake you can add something like -DCMAKE_C_FLAGS="-flto" / -DCMAKE_CXX_FLAGS="-flto" to your cmake invocation.
  2. Second, add the following linker flag: -flto -Wl,--plugin-opt=-lto-embed-bitcode=post-merge-pre-opt. In the case of CMake you can add something like -DCMAKE_EXE_LINKER_FLAGS="-flto -Wl,--plugin-opt=-lto-embed-bitcode=post-merge-pre-opt" to your cmake invocation.
  3. Build the project
  4. Let’s say an executable foo is now built. Run the following command to extract the (merged) LLVM bitcode embedded in the ELF: objcopy foo --dump-section .llvmbc=foo.bc. The extracted bitcode will be placed in foo.bc. You can use llvm-dis to get the textual LLVM IR.

Note that IIRC -lto-embed-bitcode is only exposed after LLVM 14. Also, (full) LTO will consume A LOT of memory. One way to mitigate this is using better linkers like LLD (preferred) or gold. For instance, to use LLD, add -fuse-ld=lld to the linker flag after you installed LLD.

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