Consider using Compute shaders for post-processing effects like bloom

[IntegratedQuantum]

Compute shaders are just simpler to use and in theory could be slightly faster.
Additionally compute shaders give more control over the data traversal which can improve caching:
https://computergraphics.stackexchange.com/questions/9956/performance-of-compute-shaders-vs-fragment-shaders-for-deferred-rendering