Optimizations for broadcast

[maleadt]

Fixes #298

[codecov]

Codecov Report

Merging #299 into master will decrease coverage by 0.00%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master     #299      +/-   ##
==========================================
- Coverage   77.71%   77.70%   -0.01%     
==========================================
  Files         155      155              
  Lines        8874     8873       -1     
==========================================
- Hits         6896     6895       -1     
  Misses       1978     1978              

Impacted Files	Coverage Δ
src/gpuarrays.jl	48.00% <83.33%> (-2.00%)	⬇️
lib/cudadrv/execution.jl	100.00% <100.00%> (ø)
lib/cudadrv/occupancy.jl	76.00% <100.00%> (ø)
src/compiler/execution.jl	91.59% <100.00%> (ø)

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