LLVM - Run Own Pass automatically with clang

Question

I wrote a few own passes for llvm, in order to use them with clang.

I integrated them in llvm (not dynamically loaded). They are even listed in the Optimizations available: section when I type:

opt --help-hidden

I want to run one of own my passes now automatically as the last one when I call clang:

clang ./hello.bc -o ./hello

or even with c-code:

clang ./hello.c -o ./hello

When I run my pass with opt manually, the modified ByteCode is generated and written to a new .bc file:

opt -my-pass < ./hello.bc > ./hello_optimized.bc

When I compile the modified .bc with clang, normal clang Optimizations are run again, which destroy the optimizations of my manual executed pass:

clang -O0 -m32 ./hello_optimized.bc -o ./hello_optimized

My Question is:

• How can I run my own written pass automatically with clang as the last pass of all?
• Another possible solution is deactivating all passes completely, or at least the dead code/function elimination of clang/opt. How could I do this?

Answer 1

You can run your own pass with clang directly with -Xclang.

clang++ -Xclang -load -Xclang ./libmypass.so input.cpp

Source

Answer 2

The proper way to do this would be to make clang add your pass to the pass manager it builds. See clang/lib/CodeGen/BackendUtil.cpp:void EmitAssemblyHelper::CreatePasses() for how it's handled for the sanitizers.