[llvm] [clang-tools-extra] [clang] [Clang] Fix linker error for function multiversioning (PR #71706)

[via cfe-commits]

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@@ -4114,8 +4114,26 @@ void CodeGenModule::emitMultiVersionFunctions() {
     }
 
     llvm::Constant *ResolverConstant = GetOrCreateMultiVersionResolver(GD);
-    if (auto *IFunc = dyn_cast<llvm::GlobalIFunc>(ResolverConstant))
+    if (auto *IFunc = dyn_cast<llvm::GlobalIFunc>(ResolverConstant)) {
       ResolverConstant = IFunc->getResolver();
+      // In Aarch64, default versions of multiversioned functions are mangled to
+      // their 'normal' assembly name. This deviates from other targets which
+      // append a '.default' string. As a result we need to continue appending
+      // .ifunc in Aarch64.
+      // FIXME: Should Aarch64 mangling for 'default' multiversion function and
+      // in turn ifunc function match that of other targets?
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elizabethandrews wrote:

https://gcc.gnu.org/wiki/FunctionMultiVersioning says _"The only exception to this is the default version tagged with target attribute string "default". The default version retains the original assembler name and is not changed"_ Looks like this was intentional for some reason.

It is interesting that GCC changed mangling rules for `target_clones` attribute though. The default versions do have a `.default` suffix 

https://github.com/llvm/llvm-project/pull/71706