LLVM Optimization Using C++ API - llvm

Question

I'm trying to figure out how to perform all optimizations on an LLVM Module (e.g., all -O3 optimizations). I've tried the following but I'm not sure that all possible optimizations are being applied (e.g., inlining).
//take string "llvm" (LLVM IR) and return "output_llvm" (optimized LLVM IR)
static string optimize(string llvm) {
LLVMContext &ctx = getGlobalContext();
SMDiagnostic err;
Module *ir = ParseIR(MemoryBuffer::getMemBuffer(llvm), err, ctx);
PassManager *pm = new PassManager();
PassManagerBuilder builder;
builder.OptLevel = 3;
builder.populateModulePassManager(*pm);
pm->run(*ir);
delete pm;
string output_llvm;
raw_string_ostream buff(output_llvm);
ir->print(buff, NULL);
return output_llvm;
}
Is there anything else I can do to improve the performance of the output LLVM IR?
EDIT: I have tried to add all of the optimizations from the AddOptimizationPasses() function in opt.cpp, as shown below:
PassManager *pm = new PassManager();
int optLevel = 3;
int sizeLevel = 0;
PassManagerBuilder builder;
builder.OptLevel = optLevel;
builder.SizeLevel = sizeLevel;
builder.Inliner = createFunctionInliningPass(optLevel, sizeLevel);
builder.DisableUnitAtATime = false;
builder.DisableUnrollLoops = false;
builder.LoopVectorize = true;
builder.SLPVectorize = true;
builder.populateModulePassManager(*pm);
pm->run(*module);
Also, I create a FunctionPassManager before I create the PassManager and add several passes like so:
FunctionPassManager *fpm = new FunctionPassManager(module);
// add several passes
fpm->doInitialization();
for (Function &f : *ir)
fpm->run(f);
fpm->doFinalization();
However, the performance is the same as running on the command line with -O1 whereas I can get much better performance on the command line using -O3. Any suggestions?

Answer 1

Follow the logic in the function AddOptimizationPasses in opt.cpp. This is the source of truth.

Answer 2

While looking into LLVM optimization I found this information on pass ordering and I think it's potentially telling for why someone might encounter this situation.
Depending on your language and the optimizations you're expecting, you may need to specifically tune your optimizing passes to your use-cases. In particular, the ordering of those passes may be important. For example, if your better -O3 code was optimizing completely un-optimized code or code that was already partially optimized by your program, it may just be that you need to re-order or duplicate some passes in order to the expected final result.
Given the specific wording here and the fact that Eli's answer was accepted I'm not 100% sure if this is what the OP was seeing but this knowledge may be helpful for others with similar questions who find this answer like I did.