On Mon, May 30, 2016 at 7:23 PM, David P. Sanders <dpsand...@gmail.com> wrote: > > > El lunes, 30 de mayo de 2016, 19:11:47 (UTC-4), FANG Colin escribió: >> >> function t1(n::Int, x::Int, a::Float64) >> x::Float64 = x >> for i in 1:n >> x += a >> end >> x >> end >> @time t1(10^6, 1, 1.0) >> >> 0.005445 seconds (1.00 M allocations: 15.259 MB) > > > In t1, x changes type during the function, from Int to Float64, so the > function is type *un*stable, as shown by @code_warntype, > and as suggested by the huge number of allocations. > > In t2, x is always a Float64, and the function is type stable. > >> >> >> >> >> >> function t2(n::Int, y::Int, a::Float64) >> x::Float64 = y >> for i in 1:n >> x += a >> end >> x >> end >> @time t2(10^6, 1, 1.0) >> >> 0.001044 seconds (6 allocations: 192 bytes) >> >> >> >> >> The @code_warntype of the 2 functions are very similar. However, the llvm >> code generated from t2 is a lot simpler. > > > The @code_warntype of the two functions is very *different*. (This is easier > to see in the REPL than in the notebook, if > that is the problem.) > >> >> >> Does it suggest that if we want to change the type of an argument, we'd >> better create a new variable?
This is a known bug. Fortunately it's easy to catch with code_warntype.
