[clang] [Clang][AArch64] Include SME attributes in the name mangling of function types (PR #114209)

[Sander de Smalen via cfe-commits]

================
@@ -3535,6 +3536,74 @@ void CXXNameMangler::mangleExtFunctionInfo(const FunctionType *T) {
   // FIXME: noreturn
 }
 
+enum SMEState {
+  Normal = 0,
+  SM_Enabled = 1 << 0,
+  SM_Compatible = 1 << 1,
+  ZA_Agnostic = 1 << 2,
+  ZA_Shift = 3,
+  ZT0_Shift = 6,
+  None = 0b000,
+  In = 0b001,
+  Out = 0b010,
+  InOut = 0b011,
+  Preserves = 0b100
+};
+
+unsigned encodeZAState(unsigned SMEAttrs) {
+  switch (SMEAttrs) {
+  case FunctionType::ARM_None:
+    return SMEState::None;
+  case FunctionType::ARM_In:
+    return SMEState::In;
+  case FunctionType::ARM_Out:
+    return SMEState::Out;
+  case FunctionType::ARM_InOut:
+    return SMEState::InOut;
+  case FunctionType::ARM_Preserves:
+    return SMEState::Preserves;
+  }
+  llvm_unreachable("Unrecognised SME attribute");
+}
+
+// As described in the AArch64 ACLE, the mangling scheme for function types
+// which have SME attributes is implemented as a "pseudo" template:
+//
+//   '__SME_ATTRS<<normal_function_type>, <sme_state>>'
+//
+// Combining the function type with a bitmask representing the streaming and ZA
+// properties of the function's interface.
+//
+// The mangling scheme is otherwise defined in the appendices to the Procedure
+// Call Standard for the Arm Architecture, see
+// https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#appendix-c-mangling
+//
+void CXXNameMangler::mangleSMEAttrs(unsigned SMEAttrs) {
+  if (!SMEAttrs)
+    return;
+
+  // Streaming Mode
+  unsigned Bitmask = SMEState::Normal;
----------------
sdesmalen-arm wrote:

```suggestion
  unsigned Bitmask = 0;
```

https://github.com/llvm/llvm-project/pull/114209