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

[Sander de Smalen via cfe-commits]

================
@@ -3532,6 +3533,72 @@ void CXXNameMangler::mangleExtFunctionInfo(const FunctionType *T) {
   // FIXME: noreturn
 }
 
+enum class AAPCSBitmaskSME : unsigned {
+  ArmStreamingBit = 1 << 0,
+  ArmStreamingCompatibleBit = 1 << 1,
+  ArmAgnosticSMEZAStateBit = 1 << 2,
+  ZA_Shift = 3,
+  ZT0_Shift = 6,
+  NoState = 0b000,
+  ArmIn = 0b001,
+  ArmOut = 0b010,
+  ArmInOut = 0b011,
+  ArmPreserves = 0b100,
+  LLVM_MARK_AS_BITMASK_ENUM(/*LargestValue=*/ArmPreserves)
+};
+
+static AAPCSBitmaskSME encodeAAPCSZAState(unsigned SMEAttrs) {
+  switch (SMEAttrs) {
+  case FunctionType::ARM_None:
+    return AAPCSBitmaskSME::NoState;
+  case FunctionType::ARM_In:
+    return AAPCSBitmaskSME::ArmIn;
+  case FunctionType::ARM_Out:
+    return AAPCSBitmaskSME::ArmOut;
+  case FunctionType::ARM_InOut:
+    return AAPCSBitmaskSME::ArmInOut;
+  case FunctionType::ARM_Preserves:
+    return AAPCSBitmaskSME::ArmPreserves;
+  default:
+    llvm_unreachable("Unrecognised SME attribute");
+  }
+}
+
+// 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.
+//
+// Mangling of SME keywords is described in more detail in the AArch64 ACLE:
+// https://github.com/ARM-software/acle/blob/main/main/acle.md#c-mangling-of-sme-keywords
+//
+void CXXNameMangler::mangleSMEAttrs(unsigned SMEAttrs) {
+  if (!SMEAttrs)
+    return;
+
+  unsigned Bitmask = 0;
+  if (SMEAttrs & FunctionType::SME_PStateSMEnabledMask)
+    Bitmask |= static_cast<unsigned>(AAPCSBitmaskSME::ArmStreamingBit);
----------------
sdesmalen-arm wrote:

You can remove the `static_cast` if you change `Bitmask` to `AAPCSBitmaskSME`. Then the only place that still requires a bitcast is where you print `Bitmask` to `Out`.

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