Automatically skip boundschecks in setindex! when safe to do so

[giordano]

Fix #65

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.66%. Comparing base (f62e401) to head (c387663).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #68      +/-   ##
==========================================
+ Coverage   98.64%   98.66%   +0.01%     
==========================================
  Files           1        1              
  Lines         222      225       +3     
==========================================
+ Hits          219      222       +3     
  Misses          3        3              

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[giordano]

I'm now away from keyboard, will need to double check this at another time, but if I remember correctly this PR only fixes the issue with bounds checks. Without an explicit @inbounds in front of the setindex! in the for loop the stores aren't vectorised, for some reason that I couldn't understand. Using @inbounds recovers full vectorisation, but that's not needed for Vectors. Maybe an issue for a different ticket.

Edit: I can confirm this doesn't vectorise the stores, but at least removes the bounds checks, which is the main problem reported in #65

julia> code_llvm((FixedSizeVector{Float64,Memory{Float64}},)) do v
           for idx in eachindex(v)
               v[idx] = idx
           end
       end

LLVM IR

; Function Signature: var"#23"(FixedSizeArrays.FixedSizeArray{Float64, 1, Memory{Float64}})
;  @ REPL[16]:2 within `#23`
define void @"julia_#23_3098"(ptr nocapture noundef nonnull readonly align 8 dereferenceable(16) %"v::FixedSizeArray", ptr nocapture readonly %.roots.v) #0 {
top:
; ┌ @ abstractarray.jl:321 within `eachindex`
; │┌ @ abstractarray.jl:137 within `axes1`
; ││┌ @ abstractarray.jl:98 within `axes`
; │││┌ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:64 within `size`
; ││││┌ @ Base.jl:49 within `getproperty`
       %0 = getelementptr inbounds i8, ptr %"v::FixedSizeArray", i64 8
; └└└└└
; ┌ @ range.jl:911 within `iterate`
; │┌ @ range.jl:688 within `isempty`
; ││┌ @ operators.jl:425 within `>`
; │││┌ @ int.jl:83 within `<`
      %.unbox = load i64, ptr %0, align 8
      %1 = icmp slt i64 %.unbox, 1
; └└└└
  br i1 %1, label %L48, label %L13.preheader16

L13.preheader16:                                  ; preds = %top
  %memoryref_mem = load ptr, ptr %.roots.v, align 8
  %memory_data_ptr = getelementptr inbounds { i64, ptr }, ptr %memoryref_mem, i64 0, i32 1
;  @ REPL[16]:3 within `#23`
; ┌ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:240
; │┌ @ boot.jl:544 within `memoryref`
    %memoryref_data.pre = load ptr, ptr %memory_data_ptr, align 8
; │└
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:59 within `setindex!`
   br label %L29

L29:                                              ; preds = %L29, %L13.preheader16
   %value_phi3 = phi i64 [ %4, %L29 ], [ 1, %L13.preheader16 ]
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:239
; │┌ @ number.jl:7 within `convert`
; ││┌ @ float.jl:239 within `Float64`
     %2 = sitofp i64 %value_phi3 to double
; │└└
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:240
   %memoryref_offset = shl i64 %value_phi3, 3
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:241
   %3 = getelementptr i8, ptr %memoryref_data.pre, i64 %memoryref_offset
   %memoryref_data6 = getelementptr i8, ptr %3, i64 -8
   store double %2, ptr %memoryref_data6, align 8
; └
;  @ REPL[16]:4 within `#23`
; ┌ @ range.jl:915 within `iterate`
   %4 = add nuw i64 %value_phi3, 1
; └
  %5 = icmp ult i64 %value_phi3, %.unbox
  br i1 %5, label %L29, label %L48

L48:                                              ; preds = %L29, %top
  ret void
}

Compare with

julia> code_llvm((FixedSizeVector{Float64,Memory{Float64}},)) do v
           for idx in eachindex(v)
               @inbounds v[idx] = idx
           end
       end

LLVM IR

; Function Signature: var"#26"(FixedSizeArrays.FixedSizeArray{Float64, 1, Memory{Float64}})
;  @ REPL[17]:2 within `#26`
define void @"julia_#26_3146"(ptr nocapture noundef nonnull readonly align 8 dereferenceable(16) %"v::FixedSizeArray", ptr nocapture readonly %.roots.v) #0 {
top:
; ┌ @ abstractarray.jl:321 within `eachindex`
; │┌ @ abstractarray.jl:137 within `axes1`
; ││┌ @ abstractarray.jl:98 within `axes`
; │││┌ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:64 within `size`
; ││││┌ @ Base.jl:49 within `getproperty`
       %0 = getelementptr inbounds i8, ptr %"v::FixedSizeArray", i64 8
; └└└└└
; ┌ @ range.jl:911 within `iterate`
; │┌ @ range.jl:688 within `isempty`
; ││┌ @ operators.jl:425 within `>`
; │││┌ @ int.jl:83 within `<`
      %.unbox = load i64, ptr %0, align 8
      %1 = icmp slt i64 %.unbox, 1
; └└└└
  br i1 %1, label %L48, label %L13.preheader

L13.preheader:                                    ; preds = %top
  %memoryref_mem = load ptr, ptr %.roots.v, align 8
  %memory_data_ptr = getelementptr inbounds { i64, ptr }, ptr %memoryref_mem, i64 0, i32 1
  %memoryref_data = load ptr, ptr %memory_data_ptr, align 8
;  @ REPL[17]:4 within `#26`
  %invariant.gep = getelementptr i8, ptr %memoryref_data, i64 -8
  %min.iters.check = icmp ult i64 %.unbox, 8
  br i1 %min.iters.check, label %scalar.ph, label %vector.ph

vector.ph:                                        ; preds = %L13.preheader
  %n.vec = and i64 %.unbox, 9223372036854775800
  %ind.end = or disjoint i64 %n.vec, 1
  br label %vector.body

vector.body:                                      ; preds = %vector.body, %vector.ph
  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
  %vec.ind = phi <2 x i64> [ <i64 1, i64 2>, %vector.ph ], [ %vec.ind.next, %vector.body ]
  %step.add = add <2 x i64> %vec.ind, <i64 2, i64 2>
  %step.add13 = add <2 x i64> %vec.ind, <i64 4, i64 4>
  %step.add14 = add <2 x i64> %vec.ind, <i64 6, i64 6>
;  @ REPL[17]:3 within `#26`
; ┌ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:239
; │┌ @ number.jl:7 within `convert`
; ││┌ @ float.jl:239 within `Float64`
     %2 = sitofp <2 x i64> %vec.ind to <2 x double>
     %3 = sitofp <2 x i64> %step.add to <2 x double>
     %4 = sitofp <2 x i64> %step.add13 to <2 x double>
     %5 = sitofp <2 x i64> %step.add14 to <2 x double>
; │└└
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:240
   %offset.idx = shl i64 %index, 3
   %6 = or disjoint i64 %offset.idx, 8
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:241
   %7 = getelementptr i8, ptr %invariant.gep, i64 %6
   %8 = getelementptr double, ptr %7, i64 2
   %9 = getelementptr double, ptr %7, i64 4
   %10 = getelementptr double, ptr %7, i64 6
   store <2 x double> %2, ptr %7, align 8
   store <2 x double> %3, ptr %8, align 8
   store <2 x double> %4, ptr %9, align 8
   store <2 x double> %5, ptr %10, align 8
   %index.next = add nuw i64 %index, 8
   %vec.ind.next = add <2 x i64> %vec.ind, <i64 8, i64 8>
   %11 = icmp eq i64 %index.next, %n.vec
   br i1 %11, label %middle.block, label %vector.body

middle.block:                                     ; preds = %vector.body
; └
;  @ REPL[17]:4 within `#26`
  %cmp.n = icmp eq i64 %.unbox, %n.vec
  br i1 %cmp.n, label %L48, label %scalar.ph

scalar.ph:                                        ; preds = %middle.block, %L13.preheader
  %bc.resume.val = phi i64 [ %ind.end, %middle.block ], [ 1, %L13.preheader ]
  br label %L13

L13:                                              ; preds = %L13, %scalar.ph
  %value_phi3 = phi i64 [ %13, %L13 ], [ %bc.resume.val, %scalar.ph ]
;  @ REPL[17]:3 within `#26`
; ┌ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:239
; │┌ @ number.jl:7 within `convert`
; ││┌ @ float.jl:239 within `Float64`
     %12 = sitofp i64 %value_phi3 to double
; │└└
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:240
   %memoryref_offset = shl i64 %value_phi3, 3
; │ @ /Users/mose/.julia/dev/FixedSizeArrays/src/FixedSizeArrays.jl:60 within `setindex!` @ genericmemory.jl:241
   %gep = getelementptr i8, ptr %invariant.gep, i64 %memoryref_offset
   store double %12, ptr %gep, align 8
; └
;  @ REPL[17]:4 within `#26`
; ┌ @ range.jl:915 within `iterate`
; │┌ @ promotion.jl:639 within `==`
    %.not.not = icmp eq i64 %value_phi3, %.unbox
; │└
   %13 = add nuw i64 %value_phi3, 1
; └
  br i1 %.not.not, label %L48, label %L13

L48:                                              ; preds = %L13, %middle.block, %top
  ret void
}