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

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Merged
merged 2 commits into from
Dec 4, 2024
Merged

[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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@zmodem zmodem Nov 27, 2024

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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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@zmodem zmodem Nov 27, 2024

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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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@efriedma-quic efriedma-quic Nov 28, 2024

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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.

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@efriedma-quic efriedma-quic Dec 3, 2024

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(If we wanted to, we could maybe encode this as a kind of linkage in clang/include/clang/Basic/Linkage.h . It's sort of a variation of UniqueExternal: we have an entity with external linkage, but there are restrictions on which generated code can actually refer to it. And the restriction propagates exactly the same way.)

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@MaxEW707 MaxEW707 Dec 3, 2024

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(If we wanted to, we could maybe encode this as a kind of linkage in clang/include/clang/Basic/Linkage.h . It's sort of a variation of UniqueExternal: we have an entity with external linkage, but there are restrictions on which generated code can actually refer to it. And the restriction propagates exactly the same way.)

That is a neat idea from looking at Linkage.h and how it is used.
I am going to merge this PR for now if that is ok to fix the regression and then look at this alternative for a future PR. That area of the codebase is still new to me so I am going to take a bit of time to spelunk and better understand it.