[PATCH] D124010: [llvm-cxxfilt] Unable to demangle a template argument which happens to be a null pointer

[Owen Reynolds via Phabricator via llvm-commits]

gbreynoo added a comment.

Apologies for the delay in response and thank you for your input @dblaikie and @urnathan.

In D124010#3459710 <https://reviews.llvm.org/D124010#3459710>, @dblaikie wrote:

> Should Clang be changing to not use this mangling, so it uses a mangling that matches GCC?
>
> And the demangle AST you're creating here is for an enum, and a cast from 0 to nullptr - but I'm not sure that's portable (even if it is inconsistent between producers) - nullptr_t isn't necessarily an enum, and I don't think C++ requires that you can cast 0 to nullptr_t?

I'm not sure what you mean regarding clang's use of this mangling. From my understanding this is legal in the specification and so should be handled appropriately as input?



================
Comment at: llvm/include/llvm/Demangle/ItaniumDemangle.h:4357-4360
+    // A template argument which happens to be a null pointer is mangled as if
+    // it were a literal 0 of the appropriate pointer type.
+    if (consumeIf("Dn0E"))
+      return make<EnumLiteral>(make<NameType>("std::nullptr_t"), "0");
----------------
urnathan wrote:
> Why demangle this differently to just 'nullptr'?  I notice GNU's demangler does that:
> ```
> zathras:11>c++filt _Z1fIDnLDn0EEvv
> void f<decltype(nullptr), (decltype(nullptr))0>()
> ```
> It would seem 
> ```
> if (consumeIf("Dn") && (consumeIf ('0'), consumeIf ('E'))
>   return make<NameType>("nullptr");
> return nullptr;
> ```
> would suffice?
This would output nullptr rather than decltype(nullptr) or nullptr_t. Looking at the spec "a template argument which happens to be a null pointer should mangled as if it were a literal 0 of the appropriate pointer type" which in the case of LDn0E is nullptr_t.


================
Comment at: llvm/test/tools/llvm-cxxfilt/null-pointer-template-arg.test:1-12
+# As stated in the Itanium C++ ABI mangling section:A template argument
+# which happens to be a null pointer is mangled as if it were a literal
+# 0 of the appropriate pointer type; for example, "LPi0E" or "LDn0E".
+
+# RUN: llvm-cxxfilt _Z1fIDnLDnEEvv | FileCheck %s --check-prefix=NULLPTR
+# NULLPTR: void f<std::nullptr_t, nullptr>()
+
----------------
urnathan wrote:
> demangler tests are in libcxxabi/test/test_demangle.pass.cpp you'll see there's a massive array of tuples.
> 
Thanks @urnathan the LPi0E and LDnE cases were already present so I have added the LDn0E case.


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https://reviews.llvm.org/D124010