Running multiple passes automatically with clang

Hi, I’m trying to run multiple Module Passes automatically with clang. I’ve registered each pass with the following code to run it automatically

void addModifyStubPass(const PassManagerBuilder & /* unused */,
					   legacy::PassManagerBase &PM)
	PM.add(new ModifyStubPass());

// Register the pass so `opt -modify-stub` runs it.
static RegisterPass<ModifyStubPass> A("modify-stub", "Modify Stub pass");
// Tell frontends to run the pass automatically.
static RegisterStandardPasses B(PassManagerBuilder::EP_ModuleOptimizerEarly,
static RegisterStandardPasses
	C(PassManagerBuilder::EP_EnabledOnOptLevel0, addModifyStubPass);

to run it with clang I run the command

clang -Xclang -load -Xclang -Xclang -load -Xclang ./input.c

However, this runs the first specified pass twice (in this case Pass1) instead of Pass1 followed by Pass2. How to fix this?