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

[Sameer Sahasrabuddhe via cfe-commits]

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@@ -678,6 +680,54 @@ class SIMemoryLegalizer final : public MachineFunctionPass {
   bool runOnMachineFunction(MachineFunction &MF) override;
 };
 
+static std::array<std::pair<StringLiteral, SIAtomicAddrSpace>, 3> ASNames = {{
+    {"global", SIAtomicAddrSpace::GLOBAL},
+    {"local", SIAtomicAddrSpace::LDS},
+    {"image", SIAtomicAddrSpace::SCRATCH},
+}};
+
+void diagnoseUnknownMMRAASName(const MachineInstr &MI, StringRef AS) {
+  const MachineFunction *MF = MI.getMF();
+  const Function &Fn = MF->getFunction();
+  std::string Str;
+  raw_string_ostream OS(Str);
+  OS << "unknown address space '" << AS << "'; expected one of ";
+  ListSeparator LS;
+  for (const auto &[Name, Val] : ASNames)
+    OS << LS << '\'' << Name << '\'';
+  DiagnosticInfoUnsupported BadTag(Fn, Str, MI.getDebugLoc(), DS_Warning);
+  Fn.getContext().diagnose(BadTag);
+}
+
+/// Reads \p MI's MMRAs to parse the "amdgpu-as" MMRA.
+/// If this tag isn't present, or if it has no meaningful values, returns \p
+/// Default. Otherwise returns all the address spaces concerned by the MMRA.
+static SIAtomicAddrSpace getFenceAddrSpaceMMRA(const MachineInstr &MI,
+                                               SIAtomicAddrSpace Default) {
+  static constexpr StringLiteral FenceASPrefix = "amdgpu-as";
+
+  auto MMRA = MMRAMetadata(MI.getMMRAMetadata());
+  if (!MMRA)
+    return Default;
+
+  SIAtomicAddrSpace Result = SIAtomicAddrSpace::NONE;
+  for (const auto &[Prefix, Suffix] : MMRA) {
+    if (Prefix != FenceASPrefix)
+      continue;
+
+    auto It = find_if(ASNames, [Suffix = Suffix](auto &Pair) {
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ssahasra wrote:

I didn't understand the default assignment of Suffix. Shouldn't the lambda capture it simply because the outer symbol is used inside? But anyway, this use of find_if shouldn't be necessary with StringMap.

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