Tutorial on @snoop_llvm

Julia uses the LLVM compiler to generate machine code. Typically, the two main contributors to the overall compile time are inference and LLVM, and thus together @snoop_inference and @snoop_llvm collect fairly comprehensive data on the compiler.

@snoop_llvm has a somewhat different design than @snoop_inference: while @snoop_inference runs in the same session that you'll be using for analysis (and thus requires that you remember to do the data gathering in a fresh session), @snoop_llvm spawns a fresh process to collect the data. The downside is that you get less interactivity, as the data have to be written out in intermediate forms as a text file.

Add SnoopCompileCore and SnoopCompile to your environment

Here, we'll add these packages to your default environment.

using Pkg
Pkg.add(["SnoopCompileCore", "SnoopCompile"]);

Collecting the data

Here's a simple demonstration of usage:

julia> using SnoopCompileCore
julia> @snoop_llvm "func_names.csv" "llvm_timings.yaml" begin
           using InteractiveUtils
           @eval InteractiveUtils.peakflops()
       endLaunching new julia process to run commands...
done.
julia> using SnoopCompile
julia> times, info = SnoopCompile.read_snoop_llvm("func_names.csv", "llvm_timings.yaml", tmin_secs = 0.025);ERROR: MethodError: no method matching iterate(::Nothing)
The function `iterate` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  iterate(::Test.GenericString)
   @ Test /opt/hostedtoolcache/julia/1.11.1/x64/share/julia/stdlib/v1.11/Test/src/Test.jl:2195
  iterate(::Test.GenericString, ::Integer)
   @ Test /opt/hostedtoolcache/julia/1.11.1/x64/share/julia/stdlib/v1.11/Test/src/Test.jl:2195
  iterate(::Base.MethodSpecializations)
   @ Base reflection.jl:1299
  ...

This will write two files, "func_names.csv" and "llvm_timings.yaml", in your current working directory. Let's look at what was read from these files:

julia> timesERROR: UndefVarError: `times` not defined in `Main.var"Main"`
Suggestion: check for spelling errors or missing imports.
julia> infoERROR: UndefVarError: `info` not defined in `Main.var"Main"`
Suggestion: check for spelling errors or missing imports.