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docs: perf tips: deemphasize assume in favor of UnsafeAssume.jl #2181

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14 changes: 9 additions & 5 deletions docs/src/tutorials/performance.jl
Original file line number Diff line number Diff line change
Expand Up @@ -44,18 +44,22 @@

# ### Minimise Runtime Exceptions

# Many common operations can throw errors at runtime in Julia, they often do this by branching and calling a function in that branch both of which are slow on GPUs. Using `@inbounds` when indexing into arrays will eliminate exceptions due to bounds checking. You can also use `assume` from the package LLVM.jl to get rid of exceptions, e.g.
# Many common operations can throw errors at runtime in Julia, they often do this by branching and calling a function in that branch both of which are slow on GPUs. Using `@inbounds` when indexing into arrays will eliminate exceptions due to bounds checking. More generally, one can use the functions from the [UnsafeAssume.jl](https://juliahub.com/ui/Packages/General/UnsafeAssume) package to get rid of exceptions, e.g.

# ```julia
# using LLVM.Interop
# using UnsafeAssume

# function test(x, y)
# assume(x > 0)
# div(y, x)
# @inline begin # it's necessary for the code to end up in the same function after inlining for this to work
# unsafe_assume_condition(x > 0)
# div(y, x)
# end
# end
# ```

# The `assume(x > 0)` tells the compiler that there cannot be a divide by 0 error.
# The `unsafe_assume_condition(x > 0)` tells the compiler that there cannot be a divide by 0 error.

# There's also the older `Interop.assume` function from the LLVM.jl package, having the same API as `unsafe_assume_condition`.

# For more information and examples check out [Kernel analysis and optimization](https://github.com/JuliaComputing/Training/blob/master/AdvancedGPU/2-2-kernel_analysis_optimization.ipynb).

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