[cfe-dev] [RFC] Compressing AST files by default?

[Mehdi Amini via cfe-dev]

> On Oct 20, 2016, at 2:23 AM, Ilya Palachev via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> It seems that compressing AST files with simple "gzip --fast" makes them 30-40% smaller.
> So the questions are:
> 1. Is current AST serialization format really non-compressed (only abbreviations in bit stream format)?
> 2. Is it worthwhile to compress AST by default (with -emit-ast)?
> 3. Will this break things like PCH?
> 4. What's the current trade-off between PCH compile time and disk usage? If AST compression makes compilation a bit slower, but reduces the disk usage significantly, will this be appropriate for users or not?

Is there a need for this disk usage? If the main use of AST files is C++ modules / PCH, what is a typical size for a module cache directory?
(Compression is expensive)

— 
Mehdi


> 
> LLVM already has a support for compression (functions compress/uncompress in include/llvm/Support/Compression.h).
> 
> Best regards,
> Ilya Palachev
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