Experimental bugfix for Itanium name mangling segfault

[jbcoe]

Summary

The attached patch contains a (preliminary) fix and reproduction for the bug reported here:

https://bugs.llvm.org/show_bug.cgi?id=34484

The Itanium name mangling logic does not seem to handle void(*f)(void*) function pointers as struct members when compiling C++ code. The same code works fine for C.

This patch is not fit to merge as-is but may be a useful starting point for fuller investigation

[jbcoe]

Is there anything I can do to make this patch more useful?

I could add a non-python reproduction of the issue maybe?

clang/lib/AST/ItaniumMangle.cpp

if (const NamespaceDecl *NS = dyn_cast<NamespaceDecl>(ND)) {
       if (NS->isAnonymousNamespace()) {
         // This is how gcc mangles these names.
         Out << "12_GLOBAL__N_1";
         break;
       }
     }
 
     if (const VarDecl *VD = dyn_cast<VarDecl>(ND)) {
+      const RecordType* RT = VD->getType()->getAs<RecordType>();
+      // FIXME:(jbcoe) find out why this check is needed. 
+      if (!RT)
+        break;
+
       // We must have an anonymous union or struct declaration.
-      const RecordDecl *RD =
-        cast<RecordDecl>(VD->getType()->getAs<RecordType>()->getDecl());
+      const RecordDecl *RD = cast<RecordDecl>(RT->getDecl());
 
       // Itanium C++ ABI 5.1.2:
       //
       //   For the purposes of mangling, the name of an anonymous union is
       //   considered to be the name of the first named data member found by a
       //   pre-order, depth-first, declaration-order walk of the data members of
       //   the anonymous union. If there is no such data member (i.e., if all of
       //   the data members in the union are unnamed), then there is no way for

mangled-names-crash.py

+from __future__ import print_function
+
+import clang.cindex
+
+
+def traverse(node):
+    print('L:', node.location.line, node.spelling, node.type.spelling, node.mangled_name)
+    for child in node.get_children():
+        traverse(child)
+
+with open('test.cpp', 'w') as o:
+    o.write('''struct S { 
+  void(*g)(void); 
+  void(*f)(void*); 
+};
+''')
+
+index = clang.cindex.Index.create()
+tu = index.parse('test.cpp', args=['-Werror'])
+traverse(tu.cursor)