[all-commits] [llvm/llvm-project] fe0e80: [JITLink][NFC] Store external symbols in a StringMap

[Job Noorman via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: fe0e804a4ef4fdf0ae7b2654ad4ac8d1cfafec60
      https://github.com/llvm/llvm-project/commit/fe0e804a4ef4fdf0ae7b2654ad4ac8d1cfafec60
  Author: Job Noorman <jnoorman at igalia.com>
  Date:   2023-08-29 (Tue, 29 Aug 2023)

  Changed paths:
    M llvm/include/llvm/ExecutionEngine/JITLink/JITLink.h

  Log Message:
  -----------
  [JITLink][NFC] Store external symbols in a StringMap

External symbols used to be stored in a `DenseSet`. An `assert` in
`addExternalSymbol` ensures that names of external symbols are unique.
However, for objects containing a huge number of external symbols, this
`assert` can be a performance bottleneck.

This patch proposes to store external symbols in a `StringMap` instead
making it significantly cheaper to check if a certain symbol name
already exists.

This issue came up while porting BOLT to JITLink (D147544): linking a
large binary using the JITLink port turned out to be about 4x slower
than the current version of BOLT that uses RuntimeDyld. This slowdown
was caused entirely by the `assert` in `addExternalSymbol`. Using this
patch, the JITLink port is slightly faster than RuntimeDyld.

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D150874