[llvm-dev] Default compression level for -compress-debug-info=zlib?

[via llvm-dev]

Hi Rui,

> My suggestion was to use compression level 9 when both -O2 and -compress-debug-section=zlib are specified.

The data clearly shows that beyond level 6 there is a huge increase in compute time (roughly triples) for nearly no benefit (incremental ~0.1% size reduction).  If we're going to do anything more than level 1, then I think 6 is the right place to stop.

In my experience, building for release really should not be a different process than a team normally uses.  So, we cannot rely on an argument that "building for release is rare so it's okay to make it incredibly expensive."  This reinforces the idea of using compression level 6 instead of level 9.

> As to (3), in most cases, I believe it is rare to distribute executables with debug info widely

Agreed, however debug executables are (or should be!) archived, and compressed debug info looks like it would more than double the number of versions one can archive on the same media.  Long-term storage may be cheap but it's not free.

--paulr

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