I noticed the compiler wasn't quite reducing things as it should, so here are some edits to (hopefully) improve performance. Thanks to @mbauman and @YingboMa for Slack discussion.

Suppose we have

julia> Z = Zeros(10)
10-element Zeros{Float64}

julia> f(z,j) = @inbounds z[j]
f (generic function with 1 method)

Then

Before

julia> @code_llvm f(Z,3)
;  @ REPL[5]:1 within `f`
define double @julia_f_2043([1 x [1 x [1 x i64]]]* nocapture nonnull readonly align 8 dereferenceable(8) %0, i64 signext %1) #0 {
top:
  %2 = alloca [1 x i64], align 8
; ┌ @ /home/chad/git/FillArrays.jl/src/FillArrays.jl:42 within `getindex`
; │┌ @ /home/chad/git/FillArrays.jl/src/FillArrays.jl:37 within `_fill_getindex`
    %3 = getelementptr inbounds [1 x i64], [1 x i64]* %2, i64 0, i64 0
    store i64 %1, i64* %3, align 8
; ││┌ @ abstractarray.jl:659 within `checkbounds` @ abstractarray.jl:644
; │││┌ @ abstractarray.jl:718 within `checkindex`
; ││││┌ @ int.jl:471 within `<=`
       %4 = icmp slt i64 %1, 1
; ││││└
; ││││┌ @ range.jl:686 within `last`
; │││││┌ @ Base.jl:42 within `getproperty`
        %5 = getelementptr inbounds [1 x [1 x [1 x i64]]], [1 x [1 x [1 x i64]]]* %0, i64 0, i64 0, i64 0, i64 0
; ││││└└
; ││││┌ @ int.jl:471 within `<=`
       %6 = load i64, i64* %5, align 8
       %7 = icmp slt i64 %6, %1
; │││└└
; │││ @ abstractarray.jl:659 within `checkbounds`
     %8 = or i1 %4, %7
     br i1 %8, label %L12, label %L17

L12:                                              ; preds = %top
     %9 = call nonnull {}* @j_throw_boundserror_2045([1 x [1 x [1 x i64]]]* nocapture nonnull readonly %0, [1 x i64]* nocapture readonly %2) #0
     call void @llvm.trap()
     unreachable

L17:                                              ; preds = %top
; └└└
  ret double 0.000000e+00
}

After

julia> @code_llvm f(Z,3)
;  @ REPL[5]:1 within `f`
define double @julia_f_1017([1 x [1 x [1 x i64]]]* nocapture nonnull readonly align 8 dereferenceable(8) %0, i64 signext %1) #0 {
top:
  ret double 0.000000e+00
}

Thanks! Any chance you can add tests?

Codecov Report

Merging #155 (9878b6a) into master (269fd41) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #155   +/-   ##
=======================================
  Coverage   99.21%   99.21%           
=======================================
  Files           4        4           
  Lines         633      633           
=======================================
  Hits          628      628           
  Misses          5        5           

Impacted Files	Coverage Δ
src/FillArrays.jl	99.68% <100.00%> (ø)

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Only way I can think of offhand is to redirect stdout, capture it in a string and check its length. But I'm not sure how to do that. Any ideas?

I mean, there's

help?> redirect_stdout
search: redirect_stdout redirect_stdio redirect_stdin redirect_stderr

  redirect_stdout([stream]) -> stream

  Create a pipe to which all C and Julia level stdout output will be redirected. Return a stream representing the pipe ends. Data written to
  stdout may now be read from the rd end of the pipe.

  │ Note
  │
  │  stream must be a compatible objects, such as an IOStream, TTY, Pipe, socket, or devnull.

  See also redirect_stdio.

  ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

  redirect_stdout(f::Function, stream)

  Run the function f while redirecting stdout to stream. Upon completion, stdout is restored to its prior setting.

TTY looks like closest, but I have no idea how to create one

help?> Base.TTY
  No documentation found.

  Summary
  ≡≡≡≡≡≡≡≡≡

  mutable struct Base.TTY

  Fields
  ≡≡≡≡≡≡≡≡

  handle    :: Ptr{Nothing}
  status    :: Int64
  buffer    :: IOBuffer
  cond      :: Base.GenericCondition{Base.Threads.SpinLock}
  readerror :: Any
  sendbuf   :: Union{Nothing, IOBuffer}
  lock      :: ReentrantLock
  throttle  :: Int64

  Supertype Hierarchy
  ≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡≡

  Base.TTY <: Base.LibuvStream <: IO <: Any

@dlfivefifty Maybe something like this?

julia> using FillArrays, Test

julia> function llvm_lines(a)
           f(x,j) = @inbounds x[j]
           io = IOBuffer()
           code_llvm(io, f, (typeof(a), Int))
           # countlines(io)
           count(==('\n'), String(take!(io)))
       end
llvm_lines (generic function with 1 method)

julia> @test llvm_lines(Zeros(10)) < 10
Test Passed
  Expression: llvm_lines(Zeros(10)) < 10
   Evaluated: 5 < 10

julia> @test llvm_lines(Ones(10)) < 10
Test Passed
  Expression: llvm_lines(Ones(10)) < 10
   Evaluated: 5 < 10

julia> @test llvm_lines(Fill(2.0,10)) < 10
Test Failed at REPL[65]:1
  Expression: llvm_lines(Fill(2.0, 10)) < 10
   Evaluated: 12 < 10
ERROR: There was an error during testing

Need to check on that last one again.

EDIT: Mostly it's just comments, looks ok

julia> f(z,j) = @inbounds z[j]
f (generic function with 1 method)

julia> @code_llvm f(Fill(2.0, 10), 3)
;  @ REPL[66]:1 within `f`
define double @julia_f_1329({ double, [1 x [1 x i64]] }* nocapture nonnull readonly align 8 dereferenceable(16) %0, i64 signext %1) #0 {
top:
; ┌ @ /home/chad/git/FillArrays.jl/src/FillArrays.jl:42 within `getindex`
; │┌ @ /home/chad/git/FillArrays.jl/src/FillArrays.jl:38 within `_fill_getindex`
; ││┌ @ /home/chad/git/FillArrays.jl/src/FillArrays.jl:127 within `getindex_value`
; │││┌ @ Base.jl:42 within `getproperty`
      %2 = getelementptr inbounds { double, [1 x [1 x i64]] }, { double, [1 x [1 x i64]] }* %0, i64 0, i32 0
; └└└└
  %3 = load double, double* %2, align 8
  ret double %3
}

Oh and I can make debuginfo=:none, then we get 6 lines at most.

Hmm, this works interactively but fails in the test environment with

Inbounds optimization: Test Failed at /home/chad/git/FillArrays.jl/test/runtests.jl:1337
  Expression: llvm_lines(Zeros(10)) < 10
   Evaluated: 20 < 10
Stacktrace:
 [1] macro expansion
   @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.7/Test/src/Test.jl:445 [inlined]
 [2] macro expansion
   @ ~/git/FillArrays.jl/test/runtests.jl:1337 [inlined]
 [3] macro expansion
   @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.7/Test/src/Test.jl:1282 [inlined]
 [4] top-level scope
   @ ~/git/FillArrays.jl/test/runtests.jl:1329
Inbounds optimization: Test Failed at /home/chad/git/FillArrays.jl/test/runtests.jl:1338
  Expression: llvm_lines(Ones(10)) < 10
   Evaluated: 20 < 10
Stacktrace:
 [1] macro expansion
   @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.7/Test/src/Test.jl:445 [inlined]
 [2] macro expansion
   @ ~/git/FillArrays.jl/test/runtests.jl:1338 [inlined]
 [3] macro expansion
   @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.7/Test/src/Test.jl:1282 [inlined]
 [4] top-level scope
   @ ~/git/FillArrays.jl/test/runtests.jl:1329
Inbounds optimization: Test Failed at /home/chad/git/FillArrays.jl/test/runtests.jl:1339
  Expression: llvm_lines(Fill(2.0, 10)) < 10
   Evaluated: 22 < 10
Stacktrace:
 [1] macro expansion
   @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.7/Test/src/Test.jl:445 [inlined]
 [2] macro expansion
   @ ~/git/FillArrays.jl/test/runtests.jl:1339 [inlined]
 [3] macro expansion
   @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.7/Test/src/Test.jl:1282 [inlined]
 [4] top-level scope
   @ ~/git/FillArrays.jl/test/runtests.jl:1329
Test Summary:         | Fail  Total
Inbounds optimization |    3      3
ERROR: LoadError: Some tests did not pass: 0 passed, 3 failed, 0 errored, 0 broken.
in expression starting at /home/chad/git/FillArrays.jl/test/runtests.jl:1328
ERROR: Package FillArrays errored during testing

I guess ]test must use a lower optimization setting? Not sure how we can test in that case.

You'd need PerformanceTestTools.jl to actually disable bounds checks in test.

Maybe it's not worth the hassle and we just merge?

Let me take one more pass at it. If this doesn't work I'll roll it back to just the code updates

And thanks @YingboMa , I hadn't heard of that one :)

Nope, no luck. I left the code commented out in case we can come back to it

That's not how you use PerformanceTestTools.jl. See https://github.com/YingboMa/FastBroadcast.jl/blob/master/test/runtests.jl#L84