[all-commits] [llvm/llvm-project] 8f4c78: [IR] Use map for string attributes (NFC)

[Nikita Popov via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 8f4c78dcf8a454a2a8a0fa04fe34e2162efd4a5c
      https://github.com/llvm/llvm-project/commit/8f4c78dcf8a454a2a8a0fa04fe34e2162efd4a5c
  Author: Nikita Popov <nikita.ppv at gmail.com>
  Date:   2020-04-26 (Sun, 26 Apr 2020)

  Changed paths:
    M llvm/lib/IR/AttributeImpl.h
    M llvm/lib/IR/Attributes.cpp

  Log Message:
  -----------
  [IR] Use map for string attributes (NFC)

Attributes are currently stored as a simple list. Enum attributes
additionally use a bitset to allow quickly determining whether an
attribute is set. String attributes on the other hand require a
full scan of the list. As functions tend to have a lot of string
attributes (at least when clang is used), this is a noticeable
performance issue.

This patch adds an additional name => attribute map to the
AttributeSetNode, which allows querying string attributes quickly.
This results in a 3% reduction in instructions retired on CTMark.
Changes to memory usage seem to be in the noise (attribute sets are
uniqued, and we don't tend to have more than a few dozen or hundred
unique attribute sets, so adding an extra map does not have a
noticeable cost.)

Differential Revision: https://reviews.llvm.org/D78859