[all-commits] [llvm/llvm-project] c0a922: Add parallelTransformReduce and parallelForEachError

[Reid Kleckner via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: c0a922b3db2d39f36c0c01776cce90cc160a7d62
      https://github.com/llvm/llvm-project/commit/c0a922b3db2d39f36c0c01776cce90cc160a7d62
  Author: Reid Kleckner <rnk at google.com>
  Date:   2020-11-02 (Mon, 02 Nov 2020)

  Changed paths:
    M llvm/include/llvm/Support/Parallel.h
    M llvm/unittests/Support/ParallelTest.cpp

  Log Message:
  -----------
  Add parallelTransformReduce and parallelForEachError

parallelTransformReduce is modelled on the C++17 pstl API of
std::transform_reduce, except our wrappers do not use execution policy
parameters.

parallelForEachError allows loops that contain potentially failing
operations to propagate errors out of the loop. This was one of the
major challenges I encountered while parallelizing PDB type merging in
LLD. Parallelizing a loop with parallelForEachError is not behavior
preserving: the loop will no longer stop on the first error, it will
continue working and report all errors it encounters in a list.

I plan to use this to propagate errors out of LLD's
coff::TpiSource::remapTpiWithGHashes, which currently stores errors an
error in the TpiSource object.

Differential Revision: https://reviews.llvm.org/D90639