Can a normal compiler include a MachineFunctionPass?

Code Generation Common Infrastructure
#1

Hi all, first I wanna say thank you for everything you all do! LLVM has made possible my dream of creating my own programming language, and you all are a huge part of that.

My ultimate goal is to be able to measure the stack space needed for a function and all of its callees (excluding recursive calls and indirect function pointer calls), to know how much space I need to allocate for a virtual thread, as part of Vale’s concurrency plans.

This 2013 email thread says:

If you want something that includes stack-spill slots and the like, then you’d need to write a MachineFunctionPass and examine the generated machine instructions. Alternatively, there might be a way in a MachineFunctionPass to get a pointer to a MachineFrame object and to query its size.

However, this 2015 email thread says:

A MachineFunctionPass is run by the code generator, so you can only use
it in tools like llc, clang, and libLTO.

Does this mean that I can’t make a MachineFunctionPass and invoke it via a PassManager inside my compiler, after the optimization passes?

I was able to get a regular FunctionPass to run from inside my compiler this way (well, can’t anymore, some “typeinfo for llvm::FunctionPass” undefined symbols seem to be appearing now) but MachineFunctionPass never seemed to work.

Are we really not able to make a MachineFunctionPass inside a compiler?

Thank you so much!

#2

There is currently no extension mechanism to add a MachineFunctionPass to existing target without modifying the LLVM source code. If you think there’s some reason to add such a mechanism, proposals welcome. (The relevant code in LLVM is TargetPassConfig::addMachinePasses.)

#3

Thank you! I’ll switch my efforts towards modifying the LLVM source code. You’ve saved me much wandering and struggle, thank you so much!

#4

Note for anyone else with the same ultimate goal as I had: there’s actually an llc flag named -stack-size-section which will emit the stack sizes for every function. No MachineFunctionPass needed!