Eagerly do boundscheck when indexing into CartesianIndices (#42119)

base/multidimensional.jl

@@ -357,8 +357,14 @@ module IteratorsMD
  @propagate_inbounds function Base.getindex(iter::CartesianIndices{0,R}) where {R}
  CartesianIndex()
  end
- @propagate_inbounds function Base.getindex(iter::CartesianIndices{N,R}, I::Vararg{Int, N}) where {N,R}
- CartesianIndex(getindex.(iter.indices, I))
+ @inline function Base.getindex(iter::CartesianIndices{N,R}, I::Vararg{Int, N}) where {N,R}
+ # Eagerly do boundscheck before calculating each item of the CartesianIndex so that
+ # we can pass `@inbounds` hint to inside the map and generates more efficient SIMD codes (#42115)
+ @boundscheck checkbounds(iter, I...)
+ index = map(iter.indices, I) do r, i
+ @inbounds getindex(r, i)
+ end
+ CartesianIndex(index)
  end
 
  # CartesianIndices act as a multidimensional range, so cartesian indexing of CartesianIndices

test/boundscheck_exec.jl

@@ -259,4 +259,17 @@ if bc_opt == bc_default || bc_opt == bc_off
  @test !occursin("arrayref(true", typed_40281)
 end
 
+@testset "pass inbounds meta to getindex on CartesianIndices (#42115)" begin
+ @inline getindex_42115(r, i, j) = @inbounds getindex(r, i, j)
+
+ R = CartesianIndices((5, 5))
+ if bc_opt == bc_on
+ @test_throws BoundsError getindex_42115(R, -1, -1)
+ @test_throws BoundsError getindex_42115(R, 1, -1)
+ else
+ @test getindex_42115(R, -1, -1) == CartesianIndex(-1, -1)
+ @test getindex_42115(R, 1, -1) == CartesianIndex(1, -1)
+ end
+end
+
 end