Workaround for bfloat16 parameter type demangling

LLVM releases before 20 don't recognise the Itanium mangling `DF16b` for `bfloat16`.
Replace it to the vendor-extended encoding `u6__bf16` before demangling, which all known demangler versions parse correctly as `NameType("__bf16")`.

AI-assisted: Claude Sonnet 4.6 (commercial SaaS)

Author: vmaksimo

lib/SPIRV/SPIRVUtil.cpp

@@ -696,7 +696,7 @@ static Type *parsePrimitiveType(LLVMContext &Ctx, StringRef Name) {
       .Cases("long", "unsigned long", Type::getInt64Ty(Ctx))
       .Cases("long long", "unsigned long long", Type::getInt64Ty(Ctx))
       .Case("half", Type::getHalfTy(Ctx))
-      .Case("std::bfloat16_t", Type::getBFloatTy(Ctx))
+      .Cases("std::bfloat16_t", "__bf16", Type::getBFloatTy(Ctx))
       .Case("float", Type::getFloatTy(Ctx))
       .Case("double", Type::getDoubleTy(Ctx))
       .Case("void", Type::getInt8Ty(Ctx))
@@ -877,7 +877,8 @@ parseNode(Module *M, const llvm::itanium_demangle::Node *ParamType,
     }
   } else if (auto *VendorTy = dyn_cast<VendorExtQualType>(ParamType)) {
     if (auto *NameTy = dyn_cast<NameType>(VendorTy->getTy())) {
-      if (NameTy->getName() == "std::bfloat16_t")
+      if (NameTy->getName() == "std::bfloat16_t" ||
+          NameTy->getName() == "__bf16")
         PointeeTy = llvm::Type::getBFloatTy(M->getContext());
     }
     // This is a block parameter. Decode the pointee type as if it were a
@@ -937,13 +938,32 @@ bool getParameterTypes(Function *F, SmallVectorImpl<Type *> &ArgTys,
   if (HasSret)
     ++ArgIter;
 
+  // "DF<N>b" mangling for bfloat<N> types (e.g. DF16b for bfloat16) is
+  // recognized by the demangler only starting from LLVM 20. Replace "DF16b"
+  // in the parameter section with the vendor-extended-type encoding "u6__bf16",
+  // which all known demangler versions parse correctly as NameType("__bf16").
+  std::string PatchedName;
+  StringRef MangledName(F->getName());
+  if (MangledName.contains("DF16b")) {
+    PatchedName = MangledName.str();
+    // Skip "_Z<N><name>" to search only in the parameter section.
+    size_t Start = PatchedName.find_first_not_of("0123456789", 2);
+    size_t Len = 0;
+    StringRef(PatchedName).substr(2, Start - 2).getAsInteger(10, Len);
+    size_t Pos = Start + Len;
+    while ((Pos = PatchedName.find("DF16b", Pos)) != std::string::npos) {
+      PatchedName.replace(Pos, 5, "u6__bf16");
+      Pos += 8;
+    }
+    MangledName = PatchedName;
+  }
+
   // Demangle the function arguments. If we get an input name of
   // "_Z12write_imagei20ocl_image1d_array_woDv2_iiDv4_i", then we expect
   // that Demangler.getFunctionParameters will return
   // "(ocl_image1d_array_wo, int __vector(2), int, int __vector(4))" (in other
   // words, the stuff between the parentheses if you ran C++ filt, including
   // the parentheses itself).
-  const StringRef MangledName(F->getName());
   ManglingParser<DefaultAllocator> Demangler(MangledName.begin(),
                                              MangledName.end());
   // We expect to see only function name encodings here. If it's not a function