[PATCH] D117853: [ELF] Parallelize --compress-debug-sections=zlib

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

https://maskray.me/blog/2022-01-23-compressed-debug-sections#linkers has a longer discussion why avoiding memory allocation is bad.
Note: this patch decreases memory usage because the previous `deflateBound` is wasteful (it's always larger than the input size).

> Can we do better? At one time, the compressed data is stored in two places. One in the allocated memory holding the compressed shard, the other in the memory mapped output file. It will be nice if we can avoid memory allocation. Unfortunately we need to compute the section size, otherwise we do not know the offsets of following sections and the section header table. There is no good way estimating the compressed section size without doing the compression. Technically if the section header table along with .symtab/.shstrtab/.strtab is moved before debug sections, we can compress the debug compression and append them to the output file. The output file will unfortunately be unconventional and this will not work when a linker script specifies exact orders of sections. It is just too hacky to do so much to just save a little memory.


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https://reviews.llvm.org/D117853