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

[Sander de Smalen via cfe-commits]

================
@@ -3536,35 +3536,64 @@ void CXXNameMangler::mangleExtFunctionInfo(const FunctionType *T) {
   // FIXME: noreturn
 }
 
-bool hasSharedState(unsigned SMEAttrs) {
+unsigned getZAState(unsigned SMEAttrs) {
   switch (SMEAttrs) {
   case FunctionType::ARM_In:
+    return 1;
   case FunctionType::ARM_Out:
+    return 2;
   case FunctionType::ARM_InOut:
+    return 3;
   case FunctionType::ARM_Preserves:
-    return true;
+    return 4;
   default:
-    return false;
+    return 0;
   }
 }
 
+// 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 bits of sme_state are defined as follows:
+//    0:  Streaming Mode
+//    1:  Streaming Compatible
+//    2:  ZA Agnostic
+//  3-5:  ZA State
+//  6-8:  ZT0 State
+//  9-63: 0, reserved for future type attributes.
+//
+// For example:
+//  void f(svint8_t (*fn)() __arm_streaming_compatible __arm_inout("za")) { fn(); }
+//
+// The function fn is described as '__SME_ATTRS<Fu10__SVInt8_tvE, 26u>' and mangled as:
+//
+//  "11__SME_ATTRSI" + function type mangling + "Lj" + bitmask + "EE"
+//
+//  i.e. "11__SME_ATTRSIFu10__SVInt8_tvELj26EE"
+//
 void CXXNameMangler::mangleSMEAttrs(unsigned SMEAttrs) {
   if (!SMEAttrs)
     return;
 
   // Streaming Mode
+  unsigned Bitmask = 0;
   if (SMEAttrs & FunctionType::SME_PStateSMEnabledMask)
-    Out << "Lj1E";
+    Bitmask |= 1;
----------------
sdesmalen-arm wrote:

Could you create an enum for these mask/shift values? That would also remove the need for the lengthy comment above (because the code would now represent it), and you can then link to the AAPCS for the documentation of those bits.

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