[clang] [llvm] [AMDGPU] Add amdgpu-as MMRA for fences (PR #78572)

[Sameer Sahasrabuddhe via cfe-commits]

================
@@ -678,6 +680,54 @@ class SIMemoryLegalizer final : public MachineFunctionPass {
   bool runOnMachineFunction(MachineFunction &MF) override;
 };
 
+static std::array<std::pair<StringLiteral, SIAtomicAddrSpace>, 3> ASNames = {{
----------------
ssahasra wrote:

Use StringMap for this?

https://github.com/llvm/llvm-project/pull/78572