Why is the binary compiled differently each time?

[Bach234]

When I compile with:
clang -fsycl -c test.cpp -o test-0.o
clang -fsycl -c test.cpp -o test-1.o
test-0.o and test-1.o always aren't same, they have random number in *.o files like this:
test-0.o: GLOBAL__sub_I_test_aef76b.cpp
test-1.o: GLOBAL__sub_I_test_2340a8.cpp
This feature doesn't exist in g++, I don't know why?

[al42and]

I'm not an expert, but, in short, when compiling SYCL code, clang has to do multiple stages and generate several intermediate files with such randomized names.

You can read more here: https://github.com/intel/llvm/blob/sycl/sycl/doc/design/CompilerAndRuntimeDesign.md

Or you can add -v switch to clang and see it for yourself.

Note: -save-temps flag disables this randomization and allows reproducible builds.

[Bach234]

Thank you for your help! Your answer is very useful. I will try it soon.

[AlexeySachkov]

To further add here: the "faulty" step is so-called integration footer. You can find more details in my reply here, but to summarize: our compiler replaces your main file with an intermediate (to append some code at the end of your .cpp file) and that makes the name unique for each compiler invocation. This behavior can be disabled with -fno-sycl-use-footer, but with that flag you can't use some of SYCL core and extension features.

[Bach234]

Thanks! This difference is from SourceFileName in llvm/lib/IR/Module.cpp, we can delete SourceFileName to solve this problem.