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Erich Keane
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[GH54588]Fix ItaniumMangler for NTTP unnamed unions w/ unnamed structs
As reported in #54588 and discussed in itanium-cxx-abi/cxx-abi#139 We are supposed to do a DFS, pre-order, decl-order search for a name for the union in this case. Prevoiusly we crashed because the IdentiferInfo pointer was nullptr, so this makes sure we have a name in the cases described by the ABI. I added an llvm-unreachable to cover an unexpected case at the end of the new function with information/reference to the ABI in case we come up with some way to get back to here. Differential Revision: https://reviews.llvm.org/D122820
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‎clang/lib/AST/ItaniumMangle.cpp

Lines changed: 45 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -5545,6 +5545,47 @@ static QualType getLValueType(ASTContext &Ctx, const APValue &LV) {
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return T;
55465546
}
55475547

5548+
static IdentifierInfo *getUnionInitName(SourceLocation UnionLoc,
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DiagnosticsEngine &Diags,
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const FieldDecl *FD) {
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// According to:
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// http://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangling.anonymous
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// For the purposes of mangling, the name of an anonymous union is considered
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// to be the name of the first named data member found by a pre-order,
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// depth-first, declaration-order walk of the data members of the anonymous
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// union.
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if (FD->getIdentifier())
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return FD->getIdentifier();
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// The only cases where the identifer of a FieldDecl would be blank is if the
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// field represents an anonymous record type or if it is an unnamed bitfield.
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// There is no type to descend into in the case of a bitfield, so we can just
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// return nullptr in that case.
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if (FD->isBitField())
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return nullptr;
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const CXXRecordDecl *RD = FD->getType()->getAsCXXRecordDecl();
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// Consider only the fields in declaration order, searched depth-first. We
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// don't care about the active member of the union, as all we are doing is
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// looking for a valid name. We also don't check bases, due to guidance from
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// the Itanium ABI folks.
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for (const FieldDecl *RDField : RD->fields()) {
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if (IdentifierInfo *II = getUnionInitName(UnionLoc, Diags, RDField))
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return II;
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}
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// According to the Itanium ABI: If there is no such data member (i.e., if all
5579+
// of the data members in the union are unnamed), then there is no way for a
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// program to refer to the anonymous union, and there is therefore no need to
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// mangle its name. However, we should diagnose this anyway.
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unsigned DiagID = Diags.getCustomDiagID(
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DiagnosticsEngine::Error, "cannot mangle this unnamed union NTTP yet");
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Diags.Report(UnionLoc, DiagID);
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return nullptr;
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}
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void CXXNameMangler::mangleValueInTemplateArg(QualType T, const APValue &V,
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bool TopLevel,
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bool NeedExactType) {
@@ -5628,7 +5669,10 @@ void CXXNameMangler::mangleValueInTemplateArg(QualType T, const APValue &V,
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mangleType(T);
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if (!isZeroInitialized(T, V)) {
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Out << "di";
5631-
mangleSourceName(FD->getIdentifier());
5672+
IdentifierInfo *II = (getUnionInitName(
5673+
T->getAsCXXRecordDecl()->getLocation(), Context.getDiags(), FD));
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if (II)
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mangleSourceName(II);
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mangleValueInTemplateArg(FD->getType(), V.getUnionValue(), false);
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}
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Out << 'E';

‎clang/test/CodeGenCXX/mangle-nttp-anon-union.cpp

Lines changed: 113 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,113 @@
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// RUN: %clang_cc1 -std=c++20 -emit-llvm %s -o - -triple=x86_64-linux-gnu | FileCheck %s
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// RUN: %clang_cc1 -std=c++20 -emit-llvm %s -o - -triple=x86_64-linux-gnu | llvm-cxxfilt | FileCheck %s --check-prefix DEMANGLED
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template<typename T>
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struct wrapper1 {
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union {
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struct {
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T RightName;
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};
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};
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};
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template<typename T>
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struct wrapper2 {
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union {
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struct {
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T RightName;
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};
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T WrongName;
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};
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};
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struct Base {
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int WrongName;
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};
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template <typename T>
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struct wrapper3 {
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union {
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struct : Base {
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T RightName; };
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T WrongName;
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};
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};
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template <typename T>
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struct wrapper4 {
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union {
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int RightName;
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struct {
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T WrongName;
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};
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T AlsoWrongName;
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};
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};
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template <typename T>
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struct wrapper5 {
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union {
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struct {
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struct {
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T RightName;
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};
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T WrongName;
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};
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};
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};
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template<typename T>
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struct wrapper6 {
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union {
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union{
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int : 5;
64+
T RightName;
65+
};
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};
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};
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template<auto tparam> void dummy(){}
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void uses() {
75+
// Zero init'ed cases.
76+
dummy<wrapper1<int>{}>();
77+
// CHECK: call void @_Z5dummyIXtl8wrapper1IiEEEEvv
78+
// DEMANGLED: call void @void dummy<wrapper1<int>{}>()()
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dummy<wrapper2<float>{}>();
80+
// CHECK: call void @_Z5dummyIXtl8wrapper2IfEEEEvv
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// DEMANGLED: call void @void dummy<wrapper2<float>{}>()()
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dummy<wrapper3<short>{}>();
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// CHECK: call void @_Z5dummyIXtl8wrapper3IsEEEEvv
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// DEMANGLED: call void @void dummy<wrapper3<short>{}>()()
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dummy<wrapper4<double>{}>();
86+
// CHECK: call void @_Z5dummyIXtl8wrapper4IdEEEEvv
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// DEMANGLED: call void @void dummy<wrapper4<double>{}>()()
88+
dummy<wrapper5<long long>{}>();
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// CHECK: call void @_Z5dummyIXtl8wrapper5IxEEEEvv
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// DEMANGLED: call void @void dummy<wrapper5<long long>{}>()()
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dummy<wrapper6<int>{}>();
92+
// CHECK: call void @_Z5dummyIXtl8wrapper6IiEEEEvv
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// DEMANGLED: call void @void dummy<wrapper6<int>{}>()()
94+
95+
dummy<wrapper1<double>{123.0}>();
96+
// CHECK: call void @_Z5dummyIXtl8wrapper1IdEtlNS1_Ut_Edi9RightNametlNS2_Ut_ELd405ec00000000000EEEEEEvv
97+
// DEMANGLED: call void @void dummy<wrapper1<double>{wrapper1<double>::'unnamed'{.RightName = wrapper1<double>::'unnamed'::'unnamed'{0x1.ecp+6}}}>()()
98+
dummy<wrapper2<double>{123.0}>();
99+
// CHECK: call void @_Z5dummyIXtl8wrapper2IdEtlNS1_Ut_Edi9RightNametlNS2_Ut_ELd405ec00000000000EEEEEEvv
100+
// DEMANGLED: call void @void dummy<wrapper2<double>{wrapper2<double>::'unnamed'{.RightName = wrapper2<double>::'unnamed'::'unnamed'{0x1.ecp+6}}}>()()
101+
dummy<wrapper3<double>{123, 456}>();
102+
// CHECK: call void @_Z5dummyIXtl8wrapper3IdEtlNS1_Ut_Edi9RightNametlNS2_Ut_Etl4BaseLi123EELd407c800000000000EEEEEEvv
103+
// DEMANGLED: call void @void dummy<wrapper3<double>{wrapper3<double>::'unnamed'{.RightName = wrapper3<double>::'unnamed'::'unnamed'{Base{123}, 0x1.c8p+8}}}>()()
104+
dummy<wrapper4<double>{123}>();
105+
// CHECK: call void @_Z5dummyIXtl8wrapper4IdEtlNS1_Ut_Edi9RightNameLi123EEEEEvv
106+
// DEMANGLED: call void @void dummy<wrapper4<double>{wrapper4<double>::'unnamed'{.RightName = 123}}>()()
107+
dummy<wrapper5<double>{123.0, 456.0}>();
108+
// CHECK: call void @_Z5dummyIXtl8wrapper5IdEtlNS1_Ut_Edi9RightNametlNS2_Ut_EtlNS3_Ut_ELd405ec00000000000EELd407c800000000000EEEEEEvv
109+
// DEMANGLED: call void @void dummy<wrapper5<double>{wrapper5<double>::'unnamed'{.RightName = wrapper5<double>::'unnamed'::'unnamed'{wrapper5<double>::'unnamed'::'unnamed'::'unnamed'{0x1.ecp+6}, 0x1.c8p+8}}}>()()
110+
dummy<wrapper6<double>{1}>();
111+
// CHECK: call void @_Z5dummyIXtl8wrapper6IdEtlNS1_Ut_Edi9RightNametlNS2_Ut_Edi9RightNameLd3ff0000000000000EEEEEEvv
112+
// DEMANGELD: call void @void dummy<wrapper6<double>{wrapper6<double>::'unnamed'{.RightName = wrapper6<double>::'unnamed'::'unnamed'{.RightName = 0x1p+0}}}>()()
113+
}

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