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[msabi] Mangle a template argument referring to array-to-pointer decay 

applied to an array the same as the array itself.

This follows MS ABI, and corrects a regression from the implementation
of generalized non-type template parameters, where we "forgot" how to
mangle this case.
This commit is contained in:
Richard Smith 2021-01-19 14:37:10 -08:00
parent e75a4b6ea9
commit 18e093faf7
2 changed files with 37 additions and 0 deletions
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23
clang/lib/AST/MicrosoftMangle.cpp
View File

@ -1466,6 +1466,21 @@ void MicrosoftCXXNameMangler::mangleTemplateArgs(
}
}
/// If value V (with type T) represents a decayed pointer to the first element
/// of an array, return that array.
static ValueDecl *getAsArrayToPointerDecayedDecl(QualType T, const APValue &V) {
// Must be a pointer...
if (!T->isPointerType() || !V.isLValue() || !V.hasLValuePath() ||
!V.getLValueBase())
return nullptr;
// ... to element 0 of an array.
QualType BaseT = V.getLValueBase().getType();
if (!BaseT->isArrayType() || V.getLValuePath().size() != 1 ||
V.getLValuePath()[0].getAsArrayIndex() != 0)
return nullptr;
return const_cast<ValueDecl*>(V.getLValueBase().dyn_cast<const ValueDecl*>());
}
void MicrosoftCXXNameMangler::mangleTemplateArg(const TemplateDecl *TD,
const TemplateArgument &TA,
const NamedDecl *Parm) {
@ -1576,6 +1591,14 @@ void MicrosoftCXXNameMangler::mangleTemplateArg(const TemplateDecl *TD,
break;
}
case TemplateArgument::UncommonValue:
if (ValueDecl *D = getAsArrayToPointerDecayedDecl(
TA.getUncommonValueType(), TA.getAsUncommonValue())) {
// Mangle the result of array-to-pointer decay as if it were a reference
// to the original declaration, to match MSVC's behavior. This can result
// in mangling collisions in some cases!
return mangleTemplateArg(
TD, TemplateArgument(D, TA.getUncommonValueType()), Parm);
}
Out << "$";
if (cast<NonTypeTemplateParmDecl>(Parm)
->getType()

14
clang/test/CodeGenCXX/mangle-ms-templates.cpp
View File

@ -4,6 +4,20 @@
// RUN: %clang_cc1 -std=c++17 -fms-compatibility-version=19 -emit-llvm %s -o - -fms-extensions -fdelayed-template-parsing -triple=x86_64-pc-win32 | FileCheck -check-prefix X64 %s
// RUN: %clang_cc1 -std=c++20 -fms-compatibility-version=19 -emit-llvm %s -o - -fms-extensions -fdelayed-template-parsing -triple=x86_64-pc-win32 | FileCheck -check-prefix CXX20-X64 %s
// Check that array-to-pointer decay is mangled as the underlying declaration.
extern const char arr[4] = "foo";
template<const char*> struct Decay1 {};
// CHECK: "?decay1@@3U?$Decay1@$1?arr@@3QBDB@@A"
Decay1<arr> decay1;
#if __cplusplus >= 201702L
// Note that this mangling approach can lead to collisions.
template<const void*> struct Decay2 {};
// CXX20-X64: "?decay2a@@3U?$Decay2@$1?arr@@3QBDB@@A"
Decay2<(const void*)arr> decay2a;
// CXX20-X64: "?decay2b@@3U?$Decay2@$1?arr@@3QBDB@@A"
Decay2<(const void*)&arr> decay2b;
#endif
template<typename T>
class Class {
public: