[all-commits] [llvm/llvm-project] 19edd6: [LLD][ELF] - Make compression level be dependent o...

[Georgii Rymar via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 19edd675c6321bc0447f459f427fa67ad46f5e2e
      https://github.com/llvm/llvm-project/commit/19edd675c6321bc0447f459f427fa67ad46f5e2e
  Author: Georgii Rymar <grimar at accesssoftek.com>
  Date:   2019-11-26 (Tue, 26 Nov 2019)

  Changed paths:
    M lld/ELF/OutputSections.cpp
    A lld/test/ELF/compressed-debug-level.test

  Log Message:
  -----------
  [LLD][ELF] - Make compression level be dependent on -On.

Currently LLD always use zlib compression level 6.
This patch changes it to use 1 for -O0, -O1 and 6 for -O2.

It fixes https://bugs.llvm.org/show_bug.cgi?id=44089.

There was also a thread in llvm-dev on this topic:
https://lists.llvm.org/pipermail/llvm-dev/2018-August/125020.html

Here is a table with results of building clang mentioned there:

```
Level   Time            Size
0       0m17.128s       2045081496   Z_NO_COMPRESSION
1       0m31.471s       922618584    Z_BEST_SPEED
2       0m32.659s       903642376
3       0m36.749s       890805856
4       0m41.532s       876697184
5       0m48.383s       862778576
6       1m3.176s        855251640    Z_DEFAULT_COMPRESSION
7       1m15.335s       853755920
8       2m0.561s        852497560
9       2m33.972s       852397408    Z_BEST_COMPRESSION
```

It shows that it is probably not reasonable to use values greater than 6.

Differential revision: https://reviews.llvm.org/D70658