[webkit-changes] [WebKit/WebKit] 6aa472: REGRESSION (282580 at main): 4.5MB binary size increase

[Sam Weinig]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 6aa472c27a8ade5cad6dffe3f8a809688d9d559f
      https://github.com/WebKit/WebKit/commit/6aa472c27a8ade5cad6dffe3f8a809688d9d559f
  Author: Sam Weinig <sam at webkit.org>
  Date:   2024-09-17 (Tue, 17 Sep 2024)

  Changed paths:
    M Source/WTF/wtf/Compiler.h
    M Source/WTF/wtf/StdLibExtras.h

  Log Message:
  -----------
  REGRESSION (282580 at main): 4.5MB binary size increase
https://bugs.webkit.org/show_bug.cgi?id=279498

Reviewed by Darin Adler.

The implementation of std::visit in some standard library implementations,
including the current libc++, can cause excessive code generation size.

This works around it for the case of a visit with a single variant, the
most common use case in WebKit and the one used by WTF::switchOn, by
using a switch-based implementation.

Measured locally, this is a ~10% code size improvement for WebCore.framework:

    FILE SIZE        VM SIZE
 --------------  --------------
  +0.8% +5.41Ki  +0.8% +5.41Ki    __TEXT,__const
  +105% +5.31Ki  +105% +5.31Ki    [__TEXT]
  +0.0%      +2  +0.0%      +2    __TEXT,__objc_methname
  -0.3%      -8  -0.3%      -8    __TEXT,__eh_frame
  -0.0%     -44  -0.0%     -44    __TEXT,__gcc_except_tab
  -0.0%    -198  -0.0%    -198    __TEXT,__cstring
  -0.3%    -216  -0.3%    -216    __TEXT,__unwind_info
  [ = ]       0  -0.4% -4.00Ki    [__LINKEDIT]
  -2.8% -6.79Ki  -2.8% -6.79Ki    Function Start Addresses
 -70.8% -6.98Ki -70.8% -6.98Ki    [__DATA_CONST]
  -2.1% -57.0Ki  -2.1% -57.0Ki    __DATA_CONST,__const
 -10.0% -91.6Ki -10.0% -91.6Ki    Code Signature
  -0.4%  -154Ki  -0.4%  -154Ki    __TEXT,__text
  -3.6%  -502Ki  -3.6%  -502Ki    Symbol Table
 -20.0% -10.8Mi -20.0% -10.8Mi    String Table
 -10.2% -11.5Mi -10.2% -11.5Mi    TOTAL

* Source/WTF/wtf/Compiler.h:
* Source/WTF/wtf/StdLibExtras.h:

Canonical link: https://commits.webkit.org/283806@main



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