[all-commits] [llvm/llvm-project] 8e7d77: [MC] Use subclass data for MCExpr to reduce memory...

[Nikita Popov via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 8e7d771cf9b6197c723e1ea8739563d24aca2e3c
      https://github.com/llvm/llvm-project/commit/8e7d771cf9b6197c723e1ea8739563d24aca2e3c
  Author: Nikita Popov <nikita.ppv at gmail.com>
  Date:   2020-04-15 (Wed, 15 Apr 2020)

  Changed paths:
    M llvm/include/llvm/MC/MCExpr.h
    M llvm/lib/MC/MCExpr.cpp

  Log Message:
  -----------
  [MC] Use subclass data for MCExpr to reduce memory usage

MCExpr has a bunch of free space that is currently going to waste.
Repurpose it as 24 bits of subclass data, which is enough to reduce
the size of all subclasses by 8 bytes. This gives us some respectable
savings for debuginfo builds. Here are the max-rss reductions for the
fat LTO link step:

    kc.link               238MiB   231MiB   (-2.82%)
    sqlite3.link          258MiB   250MiB   (-3.27%)
    consumer-typeset.link 152MiB   148MiB   (-2.51%)
    bullet.link           197MiB   192MiB   (-2.30%)
    tramp3d-v4.link       578MiB   567MiB   (-1.92%)
    pairlocalalign.link    92MiB    90MiB   (-1.98%)
    clamscan.link         230MiB   223MiB   (-2.81%)
    lencod.link           242MiB   235MiB   (-2.67%)
    SPASS.link            235MiB   230MiB   (-2.23%)
    7zip-benchmark.link   450MiB   435MiB   (-3.25%)

Differential Revision: https://reviews.llvm.org/D77939