[all-commits] [llvm/llvm-project] 4fce7d: [clang] Add one-entry cache for ASTContext::getDec...

[Nico Weber via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4fce7d6bfb18abfd20021e679f8fce489a6ed898
      https://github.com/llvm/llvm-project/commit/4fce7d6bfb18abfd20021e679f8fce489a6ed898
  Author: Nico Weber <thakis at chromium.org>
  Date:   2026-09-28 (Mon, 28 Sep 2026)

  Changed paths:
    M clang/include/clang/AST/ASTContext.h
    M clang/lib/AST/ASTContext.cpp

  Log Message:
  -----------
  [clang] Add one-entry cache for ASTContext::getDeclAttrs() (#226610)

In libc++, almost every decl has attributes, so ASTContext::DeclAttrs
has 50k-150k entries when using libc++. But attributes are often queried
several times in a row for the same decl (e.g. `D->hasAttr<A>() ||
D->hasAttr<B>()`). Numbers for some Chromium TUs:

                                        getDeclAttrs()  same Decl as   table
                                        calls           previous call  size
    blink logical_box_fragment.cc       19.6M           88.4%          156132
    glic_webui_contents_manager.cc      16.0M           86.1%          144545
    tflite kernels/conv.cc               6.1M           91.2%           52623

So add a one-element cache. AttrVecs are allocated separately, so
keeping a pointer to the result is safe.

Build time for 60 random Chromium TUs drawn with probability
proportional to their compile time:

    CPU time: 240.3 s => 237.4 s, -1.20%
    instructions: 2489.0e9 => 2452.9e9, -1.45%

(To check noise level, running this with the same binary twice: +-0.04%
CPU time, +-0.01% instructions.)

Every one of the 60 TUs improves, by 0.98% to 2.26% in instructions.

No behavior change.



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