[clang] [llvm] [llvm][AArch64] apple-m4 is armv9.2-a (PR #98267)

[Jon Roelofs via llvm-commits]

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@@ -161,14 +161,10 @@ struct CpuInfo {
   StringRef Name; // Name, as written for -mcpu.
   const ArchInfo &Arch;
   AArch64::ExtensionBitset
-      DefaultExtensions; // Default extensions for this CPU. These will be
-                         // ORd with the architecture defaults.
+      DefaultExtensions; // Default extensions for this CPU.
 
   AArch64::ExtensionBitset getImpliedExtensions() const {
-    AArch64::ExtensionBitset ImpliedExts;
-    ImpliedExts |= DefaultExtensions;
-    ImpliedExts |= Arch.DefaultExts;
-    return ImpliedExts;
+    return DefaultExtensions;
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jroelofs wrote:

Yes, and that idea is the problem: automatically adding default extensions kinda works for extensions that the compiler doesn't generate automatically where their use is driven by intrinsics, but as soon as you have something like SVE in the list you get incompatible codegen left and right.

https://github.com/llvm/llvm-project/pull/98267