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Improve performance when parsing symbol tables in mach-o files.

Authored by clayborg on Jun 1 2021, 9:52 PM.

Description

Improve performance when parsing symbol tables in mach-o files.

Some larger projects were loading quite slowly with the current LLDB on macOS and macOS simulator builds. I did some instrument traces and found 3 main culprits:

  • a LLDB timer that was put into a function that was called too often
  • a std::set that was keeping track of the address of symbols that were already added
  • a unnamed function generator in ObjectFile that was going slow due to allocations

In order to see this in action I ran the latest LLDB on a large application with many frameworks using the following method:

(lldb) script import time; start_time = time.perf_counter()
(lldb) file Large.app
(lldb) script print(time.perf_counter() - start_time)

I first range "sudo purge" to clear the system file caches to simulate a cold startup of the debugger, followed by two iterations with warm file caches.

Prior to this fix I was seeing the following timings:

17.68 (cold)
14.56 (warm 1)
14.52 (warm 2)

After this fix I was seeing:

11.32 (cold)
8.43 (warm 1)
8.49 (warm 2)

Differential Revision: https://reviews.llvm.org/D103504

Details

Committed
clayborgJun 2 2021, 10:31 AM
Differential Revision
D103504: Improve performance when parsing symbol tables in mach-o files.
Parents
rG8c948b18e9d8: Fix -Wsign-compare warning (NFC)
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