en Copyright 2015 Java http://172.16.0.5:8080/history/llvm-project-15.0.7/lld/test/ELF/lto/devirt_split_unit_localize.ll#2f651660 [lld:elf] Weaken the requirement for a computed binding to be STB_LOCALGiven the following scenario:```// Cat.cppstruct Animal { virtual void makeNoise() const = 0; };struct Cat : Animal { void makeNoise() const override; };extern "C" int puts(char const *);void Cat::makeNoise() const { puts("Meow"); }void doThingWithCat(Animal *a) { static_cast<Cat *>(a)->makeNoise(); }// CatUser.cppstruct Animal { virtual void makeNoise() const = 0; };struct Cat : Animal { void makeNoise() const override; };void doThingWithCat(Animal *a);void useDoThingWithCat() { Cat *d = new Cat; doThingWithCat(d);}// cat.ver{ global: _Z17useDoThingWithCatv; local: *;};$ clang++ Cat.cpp CatUser.cpp -fpic -flto=thin -fwhole-program-vtables-shared -O3 -fuse-ld=lld -Wl,--lto-whole-program-visibility-Wl,--version-script,cat.ver```We cannot devirtualize `Cat::makeNoise`. The issue is complex:Due to `-fsplit-lto-unit` and usage of type metadata, we place the Catvtable declaration into module 0 and the Cat vtable definition with typemetadata into module 1, causing duplicate entries (Undefined followed byDefined) in the `lto::InputFile::symbols()` output.In `BitcodeFile::parse`, after processing the `Undefined` then the`Defined`, the final state is `Defined`.In `BitcodeCompiler::add`, for the first symbol, `computeBinding`returns `STB_LOCAL`, then we reset it to `Undefined` because it isprevailing (`versionId` is `preserved`). For the second symbol, becausethe state is now `Undefined`, `computeBinding` returns `STB_GLOBAL`,causing `ExportDynamic` to be true and suppressing devirtualization.In D77280, the `computeBinding` change used a stricter `isDefined()`condition to make weak``Lazy` symbol work.This patch relaxes the condition to weaker `!isLazy()` to keep itworking while making the devirtualization work as well.Differential Revision: https://reviews.llvm.org/D98686 List of files: /llvm-project-15.0.7/lld/test/ELF/lto/devirt_split_unit_localize.ll Tue, 16 Mar 2021 08:33:50 +0000 Nathan Lanza <nathan@lanza.io>