https://github.com/dtcxzyw updated 
https://github.com/llvm/llvm-project/pull/135649

>From 43c487cd6206a215542a7711b1e2b5c48e4d4ecb Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2...@gmail.com>
Date: Wed, 16 Apr 2025 00:13:34 +0800
Subject: [PATCH] [Clang] Add support for GCC bound member functions extension

---
 clang/docs/ReleaseNotes.rst                   |   5 +
 clang/include/clang/AST/OperationKinds.def    |   4 +
 clang/include/clang/Basic/DiagnosticGroups.td |  32 +++---
 .../clang/Basic/DiagnosticSemaKinds.td        |   4 +
 clang/include/clang/CIR/Dialect/IR/CIROps.td  |   1 +
 clang/lib/AST/Expr.cpp                        |   7 ++
 clang/lib/AST/ExprConstant.cpp                |   2 +
 clang/lib/CIR/CodeGen/CIRGenExpr.cpp          |   1 +
 clang/lib/CodeGen/CGExpr.cpp                  |   1 +
 clang/lib/CodeGen/CGExprAgg.cpp               |   2 +
 clang/lib/CodeGen/CGExprComplex.cpp           |   1 +
 clang/lib/CodeGen/CGExprConstant.cpp          |   1 +
 clang/lib/CodeGen/CGExprScalar.cpp            |  32 ++++++
 clang/lib/CodeGen/ItaniumCXXABI.cpp           |  22 +++-
 clang/lib/Edit/RewriteObjCFoundationAPI.cpp   |   1 +
 clang/lib/Sema/SemaCast.cpp                   |  60 ++++++----
 clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp |   3 +-
 clang/test/CodeGenCXX/pmf-conversions.cpp     | 105 ++++++++++++++++++
 clang/test/SemaCXX/pmf-conversions.cpp        |  54 +++++++++
 19 files changed, 299 insertions(+), 39 deletions(-)
 create mode 100644 clang/test/CodeGenCXX/pmf-conversions.cpp
 create mode 100644 clang/test/SemaCXX/pmf-conversions.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 304d9ac3d8ab5..b3408d263335e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -93,6 +93,11 @@ C++ Language Changes
       asm((std::string_view("nop")) ::: (std::string_view("memory")));
     }
 
+- Implemented `GCC bound member functions extension 
<https://gcc.gnu.org/onlinedocs/gcc/Bound-member-functions.html>`_.
+  This extension allows extracting the function pointer from a bound pointer 
to member function.
+  It is useful to save vtable lookups when the same member function is 
executed multiple times inside a loop.
+  When using this extension, a warning is emitted unless 
``-Wno-pmf-conversions`` is passed.
+
 C++2c Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/include/clang/AST/OperationKinds.def 
b/clang/include/clang/AST/OperationKinds.def
index 790dd572a7c99..489d89a697dc3 100644
--- a/clang/include/clang/AST/OperationKinds.def
+++ b/clang/include/clang/AST/OperationKinds.def
@@ -152,6 +152,10 @@ CAST_OPERATION(MemberPointerToBoolean)
 /// many ABIs do not guarantee this on all possible intermediate types).
 CAST_OPERATION(ReinterpretMemberPointer)
 
+/// CK_BoundPointerToMemberFunctionToFunctionPointer - Convert a bound
+/// member function pointer to a function pointer.  This is a GNU extension.
+CAST_OPERATION(BoundMemberFunctionToFunctionPointer)
+
 /// CK_UserDefinedConversion - Conversion using a user defined type
 /// conversion function.
 ///    struct A { operator int(); }; int i = int(A());
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td 
b/clang/include/clang/Basic/DiagnosticGroups.td
index d97bbfee2e4d5..8e5a4cba87c95 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -795,6 +795,7 @@ def DuplicateDeclSpecifier : 
DiagGroup<"duplicate-decl-specifier">;
 def CompareDistinctPointerType : DiagGroup<"compare-distinct-pointer-types">;
 def GNUUnionCast : DiagGroup<"gnu-union-cast">;
 def GNUVariableSizedTypeNotAtEnd : 
DiagGroup<"gnu-variable-sized-type-not-at-end">;
+def GNUPMFCast : DiagGroup<"pmf-conversions">;
 def Varargs : DiagGroup<"varargs">;
 def XorUsedAsPow : DiagGroup<"xor-used-as-pow">;
 
@@ -1294,22 +1295,21 @@ def C2y : DiagGroup<"c2y-extensions">;
 def GNUBinaryLiteral : DiagGroup<"gnu-binary-literal">;
 
 // A warning group for warnings about GCC extensions.
-def GNU : DiagGroup<"gnu", [GNUAlignofExpression, GNUAnonymousStruct,
-                            GNUAutoType, GNUBinaryLiteral, GNUCaseRange,
-                            GNUComplexInteger, GNUCompoundLiteralInitializer,
-                            GNUConditionalOmittedOperand, GNUDesignator,
-                            GNUEmptyStruct,
-                            VLAExtension, GNUFlexibleArrayInitializer,
-                            GNUFlexibleArrayUnionMember, GNUFoldingConstant,
-                            GNUImaginaryConstant, GNUIncludeNext,
-                            GNULabelsAsValue, GNULineMarker, 
GNUNullPointerArithmetic,
-                            GNUOffsetofExtensions, GNUPointerArith,
-                            RedeclaredClassMember, GNURedeclaredEnum,
-                            GNUStatementExpression, GNUStaticFloatInit,
-                            GNUStringLiteralOperatorTemplate, GNUUnionCast,
-                            GNUVariableSizedTypeNotAtEnd, ZeroLengthArray,
-                            GNUZeroLineDirective,
-                            GNUZeroVariadicMacroArguments]>;
+def GNU
+    : DiagGroup<
+          "gnu", [GNUAlignofExpression, GNUAnonymousStruct, GNUAutoType,
+                  GNUBinaryLiteral, GNUCaseRange, GNUComplexInteger,
+                  GNUCompoundLiteralInitializer, GNUConditionalOmittedOperand,
+                  GNUDesignator, GNUEmptyStruct, VLAExtension,
+                  GNUFlexibleArrayInitializer, GNUFlexibleArrayUnionMember,
+                  GNUFoldingConstant, GNUImaginaryConstant, GNUIncludeNext,
+                  GNULabelsAsValue, GNULineMarker, GNUNullPointerArithmetic,
+                  GNUOffsetofExtensions, GNUPointerArith, 
RedeclaredClassMember,
+                  GNURedeclaredEnum, GNUStatementExpression, 
GNUStaticFloatInit,
+                  GNUStringLiteralOperatorTemplate, GNUUnionCast,
+                  GNUVariableSizedTypeNotAtEnd, ZeroLengthArray,
+                  GNUZeroLineDirective, GNUZeroVariadicMacroArguments,
+                  GNUPMFCast]>;
 // A warning group for warnings about code that clang accepts but gcc doesn't.
 def GccCompat : DiagGroup<"gcc-compat">;
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td 
b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 180ca39bc07e9..57ff6435daee8 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5120,6 +5120,10 @@ def err_ovl_unresolvable : Error<
 def err_bound_member_function : Error<
   "reference to non-static member function must be called"
   "%select{|; did you mean to call it with no arguments?}0">;
+def ext_bound_member_function_conversion
+    : ExtWarn<"converting the bound member function %1 to a function pointer "
+              "%2 is a GNU extension">,
+      InGroup<GNUPMFCast>;
 def note_possible_target_of_call : Note<"possible target for call">;
 def err_no_viable_destructor : Error<
   "no viable destructor found for class %0">;
diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td 
b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index 0d3c2065cd58c..7dc299827916b 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -109,6 +109,7 @@ def CK_ArrayToPointerDecay : 
I32EnumAttrCase<"array_to_ptrdecay", 11>;
 // CK_DerivedToBaseMemberPointer
 def CK_MemberPointerToBoolean : I32EnumAttrCase<"member_ptr_to_bool", 17>;
 // CK_ReinterpretMemberPointer
+// CK_BoundMemberFunctionToFunctionPointer
 // CK_UserDefinedConversion
 // CK_ConstructorConversion
 def CK_IntegralToPointer : I32EnumAttrCase<"int_to_ptr", 21>;
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 4deed08d693ac..967fb42668902 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1864,6 +1864,13 @@ bool CastExpr::CastConsistency() const {
     assert(getSubExpr()->getType()->isMemberPointerType());
     goto CheckNoBasePath;
 
+  case CK_BoundMemberFunctionToFunctionPointer:
+    assert(getType()->isFunctionPointerType());
+    assert(getSubExpr()->getType()->isMemberPointerType() ||
+           getSubExpr()->getType()->isSpecificPlaceholderType(
+               BuiltinType::BoundMember));
+    goto CheckNoBasePath;
+
   case CK_BitCast:
     // Arbitrary casts to C pointer types count as bitcasts.
     // Otherwise, we should only have block and ObjC pointer casts
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index d1cc722fb7945..b104a4e9416c0 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -15103,6 +15103,7 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) 
{
   case CK_BaseToDerivedMemberPointer:
   case CK_DerivedToBaseMemberPointer:
   case CK_ReinterpretMemberPointer:
+  case CK_BoundMemberFunctionToFunctionPointer:
   case CK_ConstructorConversion:
   case CK_IntegralToPointer:
   case CK_ToVoid:
@@ -15960,6 +15961,7 @@ bool ComplexExprEvaluator::VisitCastExpr(const CastExpr 
*E) {
   case CK_DerivedToBaseMemberPointer:
   case CK_MemberPointerToBoolean:
   case CK_ReinterpretMemberPointer:
+  case CK_BoundMemberFunctionToFunctionPointer:
   case CK_ConstructorConversion:
   case CK_IntegralToPointer:
   case CK_PointerToIntegral:
diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp 
b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
index f0732a8ea60af..a6f4541cc7e80 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -83,6 +83,7 @@ Address CIRGenFunction::emitPointerWithAlignment(const Expr 
*expr,
     case CK_NullToMemberPointer:
     case CK_NullToPointer:
     case CK_ReinterpretMemberPointer:
+    case CK_BoundMemberFunctionToFunctionPointer:
       // Common pointer conversions, nothing to do here.
       // TODO: Is there any reason to treat base-to-derived conversions
       // specially?
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 5f028f6d8c6ac..eeeb5c8f7a21f 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -5387,6 +5387,7 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) 
{
   case CK_BaseToDerivedMemberPointer:
   case CK_MemberPointerToBoolean:
   case CK_ReinterpretMemberPointer:
+  case CK_BoundMemberFunctionToFunctionPointer:
   case CK_AnyPointerToBlockPointerCast:
   case CK_ARCProduceObject:
   case CK_ARCConsumeObject:
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 87b2a73fb0c03..91fdf8a072111 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1043,6 +1043,7 @@ void AggExprEmitter::VisitCastExpr(CastExpr *E) {
   case CK_DerivedToBaseMemberPointer:
   case CK_MemberPointerToBoolean:
   case CK_ReinterpretMemberPointer:
+  case CK_BoundMemberFunctionToFunctionPointer:
   case CK_IntegralToPointer:
   case CK_PointerToIntegral:
   case CK_PointerToBoolean:
@@ -1600,6 +1601,7 @@ static bool castPreservesZero(const CastExpr *CE) {
   case CK_MemberPointerToBoolean:
   case CK_NullToMemberPointer:
   case CK_ReinterpretMemberPointer:
+  case CK_BoundMemberFunctionToFunctionPointer:
     // FIXME: ABI-dependent.
     return false;
 
diff --git a/clang/lib/CodeGen/CGExprComplex.cpp 
b/clang/lib/CodeGen/CGExprComplex.cpp
index f556594f4a9ec..008082a493a2a 100644
--- a/clang/lib/CodeGen/CGExprComplex.cpp
+++ b/clang/lib/CodeGen/CGExprComplex.cpp
@@ -575,6 +575,7 @@ ComplexPairTy ComplexExprEmitter::EmitCast(CastKind CK, 
Expr *Op,
   case CK_DerivedToBaseMemberPointer:
   case CK_MemberPointerToBoolean:
   case CK_ReinterpretMemberPointer:
+  case CK_BoundMemberFunctionToFunctionPointer:
   case CK_ConstructorConversion:
   case CK_IntegralToPointer:
   case CK_PointerToIntegral:
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp 
b/clang/lib/CodeGen/CGExprConstant.cpp
index b016c6e36d1a8..bb665e6634e5a 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -1272,6 +1272,7 @@ class ConstExprEmitter
       llvm_unreachable("builtin functions are handled elsewhere");
 
     case CK_ReinterpretMemberPointer:
+    case CK_BoundMemberFunctionToFunctionPointer:
     case CK_DerivedToBaseMemberPointer:
     case CK_BaseToDerivedMemberPointer: {
       auto C = Emitter.tryEmitPrivate(subExpr, subExpr->getType());
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp 
b/clang/lib/CodeGen/CGExprScalar.cpp
index e9a7ba509350c..b2cca91f1b733 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2581,6 +2581,38 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     return CGF.CGM.getCXXABI().EmitNullMemberPointer(MPT);
   }
 
+  case CK_BoundMemberFunctionToFunctionPointer: {
+    // Special handling bound member functions
+    if (E->isBoundMemberFunction(CGF.getContext())) {
+      auto *BO = cast<BinaryOperator>(E->IgnoreParens());
+      const Expr *BaseExpr = BO->getLHS();
+      const Expr *MemFnExpr = BO->getRHS();
+
+      const auto *MPT = MemFnExpr->getType()->castAs<MemberPointerType>();
+      const auto *FPT = MPT->getPointeeType()->castAs<FunctionProtoType>();
+      const auto *RD = MPT->getMostRecentCXXRecordDecl();
+
+      // Emit the 'this' pointer.
+      Address This = Address::invalid();
+      if (BO->getOpcode() == BO_PtrMemI)
+        This = CGF.EmitPointerWithAlignment(BaseExpr, nullptr, nullptr,
+                                            KnownNonNull);
+      else
+        This = CGF.EmitLValue(BaseExpr, KnownNonNull).getAddress();
+
+      // Get the member function pointer.
+      llvm::Value *MemFnPtr = CGF.EmitScalarExpr(MemFnExpr);
+
+      // Ask the ABI to load the callee.  Note that This is modified.
+      llvm::Value *ThisPtrForCall = nullptr;
+      CGCallee Callee = CGF.CGM.getCXXABI().EmitLoadOfMemberFunctionPointer(
+          CGF, BO, This, ThisPtrForCall, MemFnPtr, MPT);
+      return Callee.getFunctionPointer();
+    }
+
+    // fallback to the case without the base object address
+  }
+    [[fallthrough]];
   case CK_ReinterpretMemberPointer:
   case CK_BaseToDerivedMemberPointer:
   case CK_DerivedToBaseMemberPointer: {
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp 
b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 35485dc6d867f..e846ed52f8d90 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -930,7 +930,8 @@ ItaniumCXXABI::EmitMemberPointerConversion(CodeGenFunction 
&CGF,
 
   assert(E->getCastKind() == CK_DerivedToBaseMemberPointer ||
          E->getCastKind() == CK_BaseToDerivedMemberPointer ||
-         E->getCastKind() == CK_ReinterpretMemberPointer);
+         E->getCastKind() == CK_ReinterpretMemberPointer ||
+         E->getCastKind() == CK_BoundMemberFunctionToFunctionPointer);
 
   CGBuilderTy &Builder = CGF.Builder;
   QualType DstType = E->getType();
@@ -977,6 +978,8 @@ ItaniumCXXABI::EmitMemberPointerConversion(CodeGenFunction 
&CGF,
 
   // Under Itanium, reinterprets don't require any additional processing.
   if (E->getCastKind() == CK_ReinterpretMemberPointer) return src;
+  if (E->getCastKind() == CK_BoundMemberFunctionToFunctionPointer)
+    return Builder.CreateExtractValue(src, 0, "src.ptr");
 
   llvm::Constant *adj = getMemberPointerAdjustment(E);
   if (!adj) return src;
@@ -1051,7 +1054,8 @@ ItaniumCXXABI::EmitMemberPointerConversion(const CastExpr 
*E,
                                            llvm::Constant *src) {
   assert(E->getCastKind() == CK_DerivedToBaseMemberPointer ||
          E->getCastKind() == CK_BaseToDerivedMemberPointer ||
-         E->getCastKind() == CK_ReinterpretMemberPointer);
+         E->getCastKind() == CK_ReinterpretMemberPointer ||
+         E->getCastKind() == CK_BoundMemberFunctionToFunctionPointer);
 
   QualType DstType = E->getType();
 
@@ -1061,6 +1065,20 @@ ItaniumCXXABI::EmitMemberPointerConversion(const 
CastExpr *E,
 
   // Under Itanium, reinterprets don't require any additional processing.
   if (E->getCastKind() == CK_ReinterpretMemberPointer) return src;
+  if (E->getCastKind() == CK_BoundMemberFunctionToFunctionPointer) {
+    llvm::Type *PtrTy = llvm::PointerType::getUnqual(CGM.getLLVMContext());
+    llvm::Constant *FuncPtr = llvm::ConstantExpr::getIntToPtr(
+        ConstantFoldExtractValueInstruction(src, 0), PtrTy);
+
+    const auto &NewAuthInfo = CGM.getFunctionPointerAuthInfo(DstType);
+    const auto &CurAuthInfo =
+        CGM.getMemberFunctionPointerAuthInfo(E->getSubExpr()->getType());
+
+    if (!NewAuthInfo && !CurAuthInfo)
+      return FuncPtr;
+
+    return pointerAuthResignConstant(FuncPtr, CurAuthInfo, NewAuthInfo, CGM);
+  }
 
   // If the adjustment is trivial, we don't need to do anything.
   llvm::Constant *adj = getMemberPointerAdjustment(E);
diff --git a/clang/lib/Edit/RewriteObjCFoundationAPI.cpp 
b/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
index 627a1d6fb3dd5..51f1de0edae4b 100644
--- a/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
+++ b/clang/lib/Edit/RewriteObjCFoundationAPI.cpp
@@ -1054,6 +1054,7 @@ static bool rewriteToNumericBoxedExpression(const 
ObjCMessageExpr *Msg,
     case CK_DerivedToBaseMemberPointer:
     case CK_MemberPointerToBoolean:
     case CK_ReinterpretMemberPointer:
+    case CK_BoundMemberFunctionToFunctionPointer:
     case CK_ConstructorConversion:
     case CK_IntegralToPointer:
     case CK_PointerToIntegral:
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 2824dfce1572c..e6fe007b5aff2 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -150,6 +150,11 @@ namespace {
     bool isPlaceholder(BuiltinType::Kind K) const {
       return PlaceholderKind == K;
     }
+    bool isBoundPMFConversion() const {
+      return isPlaceholder(BuiltinType::BoundMember) &&
+             DestType->isFunctionPointerType() &&
+             SrcExpr.get()->isBoundMemberFunction(Self.Context);
+    }
 
     // Language specific cast restrictions for address spaces.
     void checkAddressSpaceCast(QualType SrcType, QualType DestType);
@@ -243,13 +248,11 @@ static TryCastResult TryStaticDowncast(Sema &Self, 
CanQualType SrcType,
                                        QualType OrigDestType, unsigned &msg,
                                        CastKind &Kind,
                                        CXXCastPath &BasePath);
-static TryCastResult TryStaticMemberPointerUpcast(Sema &Self, ExprResult 
&SrcExpr,
-                                               QualType SrcType,
-                                               QualType DestType,bool CStyle,
-                                               SourceRange OpRange,
-                                               unsigned &msg,
-                                               CastKind &Kind,
-                                               CXXCastPath &BasePath);
+static TryCastResult
+TryStaticMemberPointerUpcast(Sema &Self, ExprResult &SrcExpr, QualType SrcType,
+                             QualType DestType, bool CStyle,
+                             SourceRange OpRange, unsigned &msg, CastKind 
&Kind,
+                             CXXCastPath &BasePath);
 
 static TryCastResult
 TryStaticImplicitCast(Sema &Self, ExprResult &SrcExpr, QualType DestType,
@@ -1198,9 +1201,10 @@ static unsigned int checkCastFunctionType(Sema &Self, 
const ExprResult &SrcExpr,
 /// like this:
 /// char *bytes = reinterpret_cast\<char*\>(int_ptr);
 void CastOperation::CheckReinterpretCast() {
-  if (ValueKind == VK_PRValue && !isPlaceholder(BuiltinType::Overload))
-    SrcExpr = Self.DefaultFunctionArrayLvalueConversion(SrcExpr.get());
-  else
+  if (ValueKind == VK_PRValue) {
+    if (!isPlaceholder(BuiltinType::Overload) && !isBoundPMFConversion())
+      SrcExpr = Self.DefaultFunctionArrayLvalueConversion(SrcExpr.get());
+  } else
     checkNonOverloadPlaceholders();
   if (SrcExpr.isInvalid()) // if conversion failed, don't report another error
     return;
@@ -2327,6 +2331,16 @@ static TryCastResult TryReinterpretCast(Sema &Self, 
ExprResult &SrcExpr,
     return TC_Success;
   }
 
+  // GNU extension: check if we can convert a pmf to a function pointer
+  if (DestType->isFunctionPointerType() &&
+      (SrcType->isMemberFunctionPointerType() ||
+       SrcExpr.get()->isBoundMemberFunction(Self.Context)) &&
+      Self.Context.getTargetInfo().getCXXABI().isItaniumFamily()) {
+    Kind = CK_BoundMemberFunctionToFunctionPointer;
+    msg = diag::ext_bound_member_function_conversion;
+    return TC_Extension;
+  }
+
   // See below for the enumeral issue.
   if (SrcType->isNullPtrType() && DestType->isIntegralType(Self.Context)) {
     // C++0x 5.2.10p4: A pointer can be explicitly converted to any integral
@@ -2693,9 +2707,11 @@ void CastOperation::CheckCXXCStyleCast(bool 
FunctionalStyle,
       return;
     }
 
-    checkNonOverloadPlaceholders();
-    if (SrcExpr.isInvalid())
-      return;
+    if (!isBoundPMFConversion()) {
+      checkNonOverloadPlaceholders();
+      if (SrcExpr.isInvalid())
+        return;
+    }
   }
 
   // C++ 5.2.9p4: Any expression can be explicitly converted to type "cv void".
@@ -2733,7 +2749,7 @@ void CastOperation::CheckCXXCStyleCast(bool 
FunctionalStyle,
   }
 
   if (ValueKind == VK_PRValue && !DestType->isRecordType() &&
-      !isPlaceholder(BuiltinType::Overload)) {
+      !isPlaceholder(BuiltinType::Overload) && !isBoundPMFConversion()) {
     SrcExpr = Self.DefaultFunctionArrayLvalueConversion(SrcExpr.get());
     if (SrcExpr.isInvalid())
       return;
@@ -2791,12 +2807,16 @@ void CastOperation::CheckCXXCStyleCast(bool 
FunctionalStyle,
       return;
 
     if (tcr == TC_NotApplicable) {
-      // ... or if that is not possible, a static_cast, ignoring const and
-      // addr space, ...
-      tcr = TryStaticCast(Self, SrcExpr, DestType, CCK, OpRange, msg, Kind,
-                          BasePath, ListInitialization);
-      if (SrcExpr.isInvalid())
-        return;
+      // FIXME: Bound member function to function pointer conversion is blocked
+      // by an immediate error inside ``Sema::CheckPlaceholderExpr``.
+      if (!isBoundPMFConversion()) {
+        // ... or if that is not possible, a static_cast, ignoring const and
+        // addr space, ...
+        tcr = TryStaticCast(Self, SrcExpr, DestType, CCK, OpRange, msg, Kind,
+                            BasePath, ListInitialization);
+        if (SrcExpr.isInvalid())
+          return;
+      }
 
       if (tcr == TC_NotApplicable) {
         // ... and finally a reinterpret_cast, ignoring const and addr space.
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp 
b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
index 3d0a69a515ab8..d28752febce43 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
@@ -524,7 +524,8 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const 
Expr *Ex,
       case CK_VectorSplat:
       case CK_HLSLElementwiseCast:
       case CK_HLSLAggregateSplatCast:
-      case CK_HLSLVectorTruncation: {
+      case CK_HLSLVectorTruncation:
+      case CK_BoundMemberFunctionToFunctionPointer: {
         QualType resultType = CastE->getType();
         if (CastE->isGLValue())
           resultType = getContext().getPointerType(resultType);
diff --git a/clang/test/CodeGenCXX/pmf-conversions.cpp 
b/clang/test/CodeGenCXX/pmf-conversions.cpp
new file mode 100644
index 0000000000000..c224870b19ff9
--- /dev/null
+++ b/clang/test/CodeGenCXX/pmf-conversions.cpp
@@ -0,0 +1,105 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py 
UTC_ARGS: --check-globals all --version 5
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -Wno-pmf-conversions %s -O3 
-emit-llvm -o - | FileCheck %s
+
+struct A {
+  int data;
+//.
+// CHECK: @method = local_unnamed_addr global ptr @_ZN1A6methodEv, align 8
+//.
+// CHECK-LABEL: define linkonce_odr noundef i32 @_ZN1A6methodEv(
+// CHECK-SAME: ptr noundef nonnull align 8 dereferenceable(12) [[THIS:%.*]]) 
#[[ATTR0:[0-9]+]] comdat align 2 {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret i32 0
+//
+  int method() { return 0; }
+  virtual int virtual_method() { return 1; }
+  virtual ~A() = default;
+};
+
+struct C {
+  int data;
+};
+
+struct B : C, A {
+  virtual int virtual_method() override { return 2; }
+};
+
+using pmf_type = int (A::*)();
+using pf_type = int (*)(A*);
+
+pf_type method = reinterpret_cast<pf_type>(&A::method);
+
+// CHECK-LABEL: define dso_local noundef ptr @_Z11convert_pmfP1AMS_FivE(
+// CHECK-SAME: ptr noundef readonly captures(none) [[P:%.*]], i64 
[[METHOD_COERCE0:%.*]], i64 [[METHOD_COERCE1:%.*]]) local_unnamed_addr 
#[[ATTR1:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[TMP0:%.*]] = and i64 [[METHOD_COERCE0]], 1
+// CHECK-NEXT:    [[MEMPTR_ISVIRTUAL_NOT:%.*]] = icmp eq i64 [[TMP0]], 0
+// CHECK-NEXT:    br i1 [[MEMPTR_ISVIRTUAL_NOT]], label 
%[[MEMPTR_NONVIRTUAL:.*]], label %[[MEMPTR_VIRTUAL:.*]]
+// CHECK:       [[MEMPTR_VIRTUAL]]:
+// CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[P]], i64 
[[METHOD_COERCE1]]
+// CHECK-NEXT:    [[VTABLE:%.*]] = load ptr, ptr [[TMP1]], align 8, !tbaa 
[[TBAA2:![0-9]+]]
+// CHECK-NEXT:    [[TMP2:%.*]] = getelementptr i8, ptr [[VTABLE]], i64 
[[METHOD_COERCE0]]
+// CHECK-NEXT:    [[TMP3:%.*]] = getelementptr i8, ptr [[TMP2]], i64 -1
+// CHECK-NEXT:    [[MEMPTR_VIRTUALFN:%.*]] = load ptr, ptr [[TMP3]], align 8, 
!nosanitize [[META5:![0-9]+]]
+// CHECK-NEXT:    br label %[[MEMPTR_END:.*]]
+// CHECK:       [[MEMPTR_NONVIRTUAL]]:
+// CHECK-NEXT:    [[MEMPTR_NONVIRTUALFN:%.*]] = inttoptr i64 
[[METHOD_COERCE0]] to ptr
+// CHECK-NEXT:    br label %[[MEMPTR_END]]
+// CHECK:       [[MEMPTR_END]]:
+// CHECK-NEXT:    [[TMP4:%.*]] = phi ptr [ [[MEMPTR_VIRTUALFN]], 
%[[MEMPTR_VIRTUAL]] ], [ [[MEMPTR_NONVIRTUALFN]], %[[MEMPTR_NONVIRTUAL]] ]
+// CHECK-NEXT:    ret ptr [[TMP4]]
+//
+pf_type convert_pmf(A* p, pmf_type method) {
+  return reinterpret_cast<pf_type>(p->*method);
+}
+
+// CHECK-LABEL: define dso_local noundef nonnull ptr @_Z17convert_pmf_constP1A(
+// CHECK-SAME: ptr noundef readnone captures(none) [[P:%.*]]) 
local_unnamed_addr #[[ATTR2:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    ret ptr @_ZN1A6methodEv
+//
+pf_type convert_pmf_const(A* p) {
+  return reinterpret_cast<pf_type>(p->*(&A::method));
+}
+
+// CHECK-LABEL: define dso_local noundef ptr @_Z18convert_vpmf_constP1A(
+// CHECK-SAME: ptr noundef readonly captures(none) [[P:%.*]]) 
local_unnamed_addr #[[ATTR1]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[VTABLE:%.*]] = load ptr, ptr [[P]], align 8, !tbaa 
[[TBAA2]]
+// CHECK-NEXT:    [[MEMPTR_VIRTUALFN:%.*]] = load ptr, ptr [[VTABLE]], align 
8, !nosanitize [[META5]]
+// CHECK-NEXT:    ret ptr [[MEMPTR_VIRTUALFN]]
+//
+pf_type convert_vpmf_const(A* p) {
+  return reinterpret_cast<pf_type>(p->*(&A::virtual_method));
+}
+
+// CHECK-LABEL: define dso_local noundef range(i32 0, 2) i32 
@_Z21call_b_virtual_methodP1B(
+// CHECK-SAME: ptr noundef [[P:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[VTABLE_I:%.*]] = load ptr, ptr [[P]], align 8, !tbaa 
[[TBAA2]]
+// CHECK-NEXT:    [[MEMPTR_VIRTUALFN_I:%.*]] = load ptr, ptr [[VTABLE_I]], 
align 8, !nosanitize [[META5]]
+// CHECK-NEXT:    [[CALL1:%.*]] = tail call noundef i32 
[[MEMPTR_VIRTUALFN_I]](ptr noundef nonnull [[P]]) #[[ATTR3:[0-9]+]]
+// CHECK-NEXT:    [[VTABLE:%.*]] = load ptr, ptr [[P]], align 8, !tbaa 
[[TBAA2]]
+// CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[VTABLE]], align 8
+// CHECK-NEXT:    [[CALL2:%.*]] = tail call noundef i32 [[TMP0]](ptr noundef 
nonnull align 8 dereferenceable(16) [[P]]) #[[ATTR3]]
+// CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[CALL1]], [[CALL2]]
+// CHECK-NEXT:    [[CONV:%.*]] = zext i1 [[CMP]] to i32
+// CHECK-NEXT:    ret i32 [[CONV]]
+//
+int call_b_virtual_method(B* p) {
+  return convert_pmf(p, &A::virtual_method)(p) == p->virtual_method();
+}
+
+//.
+// CHECK: attributes #[[ATTR0]] = { mustprogress nounwind 
"min-legal-vector-width"="0" "no-trapping-math"="true" 
"stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" 
}
+// CHECK: attributes #[[ATTR1]] = { mustprogress nofree norecurse nosync 
nounwind willreturn memory(read, inaccessiblemem: none) 
"min-legal-vector-width"="0" "no-trapping-math"="true" 
"stack-protector-buffer-size"="8" "target-features"="+cx8,+mmx,+sse,+sse2,+x87" 
}
+// CHECK: attributes #[[ATTR2]] = { mustprogress nofree norecurse nosync 
nounwind willreturn memory(none) "min-legal-vector-width"="0" 
"no-trapping-math"="true" "stack-protector-buffer-size"="8" 
"target-features"="+cx8,+mmx,+sse,+sse2,+x87" }
+// CHECK: attributes #[[ATTR3]] = { nounwind }
+//.
+// CHECK: [[META0:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
+// CHECK: [[META1:![0-9]+]] = !{!"{{.*}}clang version {{.*}}"}
+// CHECK: [[TBAA2]] = !{[[META3:![0-9]+]], [[META3]], i64 0}
+// CHECK: [[META3]] = !{!"vtable pointer", [[META4:![0-9]+]], i64 0}
+// CHECK: [[META4]] = !{!"Simple C++ TBAA"}
+// CHECK: [[META5]] = !{}
+//.
diff --git a/clang/test/SemaCXX/pmf-conversions.cpp 
b/clang/test/SemaCXX/pmf-conversions.cpp
new file mode 100644
index 0000000000000..bee54327e36b2
--- /dev/null
+++ b/clang/test/SemaCXX/pmf-conversions.cpp
@@ -0,0 +1,54 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -fsyntax-only %s -verify
+
+struct S {
+  int a;
+  void method();
+  void method_overload();
+  void method_overload(int);
+};
+
+using pmf_type = void (S::*)();
+using pm_type = int S::*;
+using pf_type = void (*)(S*);
+using pf_type_mismatched = void (*)(S*, int);
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wpmf-conversions"
+
+// constexpr pmf conversions are not supported yet.
+constexpr pf_type method_constexpr = reinterpret_cast<pf_type>(&S::method); // 
expected-error {{constexpr variable 'method_constexpr' must be initialized by a 
constant expression}} expected-note {{reinterpret_cast is not allowed in a 
constant expression}}
+pf_type method = reinterpret_cast<pf_type>(&S::method);
+
+void pmf_convert_no_object(pmf_type method, pm_type field) {
+  (void)reinterpret_cast<pf_type>(&S::method);
+  (void)reinterpret_cast<pf_type>(method);
+  (void)reinterpret_cast<pf_type>(((method)));
+  (void)(pf_type)(&S::method);
+  (void)(pf_type)(method);
+  (void)reinterpret_cast<pf_type_mismatched>(&S::method);
+  (void)reinterpret_cast<pf_type_mismatched>(method);
+  (void)reinterpret_cast<pf_type>(&S::a); // expected-error {{reinterpret_cast 
from 'int S::*' to 'pf_type' (aka 'void (*)(S *)') is not allowed}}
+  (void)reinterpret_cast<pf_type>(field); // expected-error {{reinterpret_cast 
from 'pm_type' (aka 'int S::*') to 'pf_type' (aka 'void (*)(S *)') is not 
allowed}}
+}
+
+void pmf_convert_with_base(S* p, S& r, pmf_type method, pm_type field) {
+  (void)reinterpret_cast<pf_type>(p->*(&S::method));
+  (void)reinterpret_cast<pf_type>(((p)->*((&S::method))));
+  (void)reinterpret_cast<pf_type>(p->*method);
+  (void)reinterpret_cast<pf_type>(((p)->*(method)));
+  
(void)reinterpret_cast<pf_type>(p->*(static_cast<pmf_type>(&S::method_overload)));
+  (void)(pf_type)(p->*(&S::method));
+  (void)(pf_type)(p->*method);
+  (void)reinterpret_cast<pf_type_mismatched>(p->*method);
+  (void)reinterpret_cast<pf_type>(r.*method);
+  (void)reinterpret_cast<pf_type_mismatched>(r.*method);
+  (void)reinterpret_cast<pf_type>(p->*(&S::a));
+  (void)reinterpret_cast<pf_type>(p->*field);
+}
+
+#pragma clang diagnostic pop
+
+void pmf_convert_warning(S *p, pmf_type method) {
+  (void)reinterpret_cast<pf_type>(method); // expected-warning {{converting 
the bound member function 'pmf_type' (aka 'void (S::*)()') to a function 
pointer 'pf_type' (aka 'void (*)(S *)') is a GNU extension}}
+  (void)reinterpret_cast<pf_type>(p->*method); // expected-warning 
{{converting the bound member function '<bound member function type>' to a 
function pointer 'pf_type' (aka 'void (*)(S *)') is a GNU extension}}
+}

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