[llvm] [LLVM]Add read and write inaccessible memory metadata (PR #154141)

[Antonio Frighetto via llvm-commits]

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@@ -56,6 +56,11 @@ enum class ModRefInfo : uint8_t {
 /// Debug print ModRefInfo.
 LLVM_ABI raw_ostream &operator<<(raw_ostream &OS, ModRefInfo MR);
 
+enum class InaccessibleTargetMemLocation {
+  AARCH64_FPMR = 3,
+  AARCH64_ZA = 4,
+};
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antoniofrighetto wrote:

I still somewhat think we shouldn't embed target-specific bits in IRMemLocation (or at least, I'm not sure having a enum class is a nice idea, doesn't look extendable to other architectures).

@nikic Would it make sense to extend MemoryEffectsBase with a optional storage to maintain target tags (e.g., a vector of `std::pair<TargetMemID, ModRefInfo>`)? The parser/reader could then leverage something similar to getOrInsertSyncScopeID from LLVMContext (i.e., `getOrInsertTargetMemTag("aarch64.za")` to have the TargetMemID, to work on unsigned rather than strings).

https://github.com/llvm/llvm-project/pull/154141