Stream: cranelift

Topic: Troubleshooting slow compile times

Tim Ngo (Nov 09 2022 at 11:36):

Hey! I'm using Cranelift as a backend for a language I'm working on. I also have an LLVM backend (via Inkwell). While messing around with some test code, I noticed that for a very large function (10000+ lines), my Cranelift backend takes longer (4.0s) to generate code than my LLVM backend (1.5s). Here's my crude test case source, which continues on for about 10000 lines:

Screenshot-2022-11-09-032154.png

Which results in CLIR that looks like this:

Screenshot-2022-11-09-032240.png

And LLVM IR that looks like this:

Screenshot-2022-11-09-032702.png

I'm wondering if there might be something very wrong with my code generation process or there are some best practices I might have missed that could account for the difference. Most of the 4 seconds is spent in ObjectModule::define_function. Is this sort of large inline function a special case?

bjorn3 (Nov 09 2022 at 15:29):

define_function is the function that does the actual compilation from clif ir to machine code. I believe you can get the timings of individual compilation passes using println!("{}", cranelift_codegen::timing::take_current()) after the define_function call.

Jamey Sharp (Nov 09 2022 at 16:50):

Could you open a GitHub issue and attach the generated CLIF? We've been working on compile-time performance improvements and it sounds like this would be an interesting test case to investigate.

Tim Ngo (Nov 09 2022 at 19:37):

Here are the timing results:

define_function main: 3.4641968s
======== ========  ==================================
   Total     Self  Pass
-------- --------  ----------------------------------
   1.090    0.696  Verify Cranelift IR
   0.314    0.314  Verify CPU flags
   6.916    0.161  Compilation passes
   0.040    0.040  Control flow graph
   0.060    0.060  Dominator tree
   0.000    0.000  Remove unreachable blocks
   0.009    0.009  Remove constant phi-nodes
   0.466    0.466  VCode lowering
   0.225    0.225  VCode emission
   0.001    0.001  VCode emission finalization
   1.487    1.487  Register allocation
======== ========  ==================================

And here's the GitHub issue: #5237

Last updated: Dec 23 2024 at 12:05 UTC