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[Clang][AST] Fix MS Mangle concept uneval context template instantiation crash #117845

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[Clang][AST] Fix MS Mangle concept uneval context template instantiation crash #117845

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58a2620
Fix MS Mangle concept uneval context template instantiation crash
MaxEW707 Nov 27, 2024
daf0610
Move to CodeGenCXX
MaxEW707 Nov 28, 2024
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10 changes: 9 additions & 1 deletion clang/lib/AST/MicrosoftMangle.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3374,7 +3374,15 @@ void MicrosoftCXXNameMangler::mangleType(const MemberPointerType *T,

void MicrosoftCXXNameMangler::mangleType(const TemplateTypeParmType *T,
Qualifiers, SourceRange Range) {
Error(Range.getBegin(), "template type parameter type") << Range;
Out << '?';

llvm::SmallString<64> Name;
Name += "<TTPT_";
Name += llvm::utostr(T->getDepth());
Name += "_";
Name += llvm::utostr(T->getIndex());
Name += ">";
mangleSourceName(Name);
}

void MicrosoftCXXNameMangler::mangleType(const SubstTemplateTypeParmPackType *T,
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25 changes: 25 additions & 0 deletions clang/test/AST/ms-uneval-context-crash.cpp
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@@ -0,0 +1,25 @@
// RUN: %clang_cc1 -std=c++20 -fms-compatibility -fms-compatibility-version=19.33 -emit-llvm %s -o - -triple=x86_64-windows-msvc | FileCheck %s
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I think doing codegen (-emit-llvm) in clang/test/AST/ is unusual, those tests normally just look at the AST (though there are exceptions). Maybe there is a better place for this?


template <typename T>
concept C = requires
{
{ T::test([](){}) };
};

template<typename T>
struct Widget {};

template <C T>
struct Widget<T> {};

struct Baz
{
template<typename F>
static constexpr decltype(auto) test(F&&) {}
};

void test()
{
Widget<Baz> w;
}
// CHECK: @"?test@@YAXXZ"
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I suppose the mangling you're adding doesn't actually show up anywhere since it's only used for a concept? But then why do we need to mangle it in the first place?

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Once we get to CodeGen, the method looks like a regular method, except for the fact that one of the template arguments is a class defined inside a concept instantiation. And CodeGen doesn't have any way to check for "is a template argument a class defined inside a concept". So, like all other methods, we stick it into DeferredDecls. And the key for the DeferredDecls map is the mangled name.

We end up trying to mangle a TemplateTypeParmType because we stick the instantiated class into the scope of an uninstantiated class template.

So no, we don't actually need to mangle it, but there's currently no way for CodeGen to check for this situation.