Re: JIT compiling with LLVM v9.0

Hi,

On 2018-01-26 13:06:27 +0300, Konstantin Knizhnik wrote:
> One more question: do you have any idea how to profile JITed code?

Yes ;). It depends a bit on what exactly you want to do. Is it
sufficient to get time associated with the parent caller, or do you need
instruction-level access.

> There is no LLVMOrcRegisterPerf in LLVM 5, so jit_profiling_support option
> does nothing.

Right, it's a patch I'm trying to get into the next version of
llvm. With that you get access to the shared object and everything.

> And without it perf is not able to unwind stack trace for generated
> code.

You can work around that by using --call-graph lbr with a sufficiently
new perf. That'll not know function names et al, but at least the parent
will be associated correctly.

> But you are compiling code using LLVMOrcAddEagerlyCompiledIR
> and I find no way to pass no-omit-frame pointer option here.

It shouldn't be too hard to open code support for it, encapsulated in a
function:
// Set function attribute "no-frame-pointer-elim" based on
// NoFramePointerElim.
for (auto &F : *Mod) {
auto Attrs = F.getAttributes();
StringRef Value(options.NoFramePointerElim ? "true" : "false");
Attrs = Attrs.addAttribute(F.getContext(), AttributeList::FunctionIndex,
"no-frame-pointer-elim", Value);
F.setAttributes(Attrs);
}
that's all that option did for mcjit.

Greetings,

Andres Freund