1 files changed, 12 insertions, 2 deletions
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index bd9e882dac4..08c86176abc 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -45,6 +45,7 @@ class ItaniumCXXABI : public CodeGen::CGCXXABI {
 protected:
   bool UseARMMethodPtrABI;
   bool UseARMGuardVarABI;
+  bool Use32BitVTableOffsetABI;
 
   ItaniumMangleContext &getMangleContext() {
     return cast<ItaniumMangleContext>(CodeGen::CGCXXABI::getMangleContext());
@@ -55,7 +56,8 @@ public:
                 bool UseARMMethodPtrABI = false,
                 bool UseARMGuardVarABI = false) :
     CGCXXABI(CGM), UseARMMethodPtrABI(UseARMMethodPtrABI),
-    UseARMGuardVarABI(UseARMGuardVarABI) { }
+    UseARMGuardVarABI(UseARMGuardVarABI),
+    Use32BitVTableOffsetABI(false) { }
 
   bool classifyReturnType(CGFunctionInfo &FI) const override;
 
@@ -425,7 +427,9 @@ public:
 
 class iOS64CXXABI : public ARMCXXABI {
 public:
-  iOS64CXXABI(CodeGen::CodeGenModule &CGM) : ARMCXXABI(CGM) {}
+  iOS64CXXABI(CodeGen::CodeGenModule &CGM) : ARMCXXABI(CGM) {
+    Use32BitVTableOffsetABI = true;
+  }
 
   // ARM64 libraries are prepared for non-unique RTTI.
   bool shouldRTTIBeUnique() const override { return false; }
@@ -579,9 +583,15 @@ llvm::Value *ItaniumCXXABI::EmitLoadOfMemberFunctionPointer(
     CGF.GetVTablePtr(Address(This, VTablePtrAlign), VTableTy, RD);
 
   // Apply the offset.
+  // On ARM64, to reserve extra space in virtual member function pointers,
+  // we only pay attention to the low 32 bits of the offset.
   llvm::Value *VTableOffset = FnAsInt;
   if (!UseARMMethodPtrABI)
     VTableOffset = Builder.CreateSub(VTableOffset, ptrdiff_1);
+  if (Use32BitVTableOffsetABI) {
+    VTableOffset = Builder.CreateTrunc(VTableOffset, CGF.Int32Ty);
+    VTableOffset = Builder.CreateZExt(VTableOffset, CGM.PtrDiffTy);
+  }
   VTable = Builder.CreateGEP(VTable, VTableOffset);
 
   // Load the virtual function to call.