[all-commits] [llvm/llvm-project] 20105b: [clang] Speedup line offset mapping computation

[serge-sans-paille via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 20105b6b4874a85813f7a4a3d8ad2a0f023dda14
      https://github.com/llvm/llvm-project/commit/20105b6b4874a85813f7a4a3d8ad2a0f023dda14
  Author: serge-sans-paille <sguelton at redhat.com>
  Date:   2021-04-08 (Thu, 08 Apr 2021)

  Changed paths:
    M clang/lib/Basic/SourceManager.cpp

  Log Message:
  -----------
  [clang] Speedup line offset mapping computation

Clang spends a decent amount of time in the LineOffsetMapping::get(...)
function. This function used to be vectorized (through SSE2) then the
optimization got dropped because the sequential version was on-par performance
wise.

This provides an optimization of the sequential version that works on a word at
a time, using (documented) bithacks to provide a portable vectorization.

When preprocessing the sqlite amalgamation, this yields a sweet 3% speedup.

This is a recommit of 6951b72334bbe4c189c71751edc1e361d7b5632c with endianness
and unsigned long vs uint64_t issues fixed (hopefully).

Differential Revision: https://reviews.llvm.org/D99409