[CodeGen] Make non-COMDAT relative vtable internal instead of private

clang/lib/CodeGen/CGVTables.cpp

@@ -1013,7 +1013,7 @@ void CodeGenVTables::RemoveHwasanMetadata(llvm::GlobalValue *GV) const {
 // the VTable does not need a relocation and move into rodata. A frequent
 // time this can occur is for classes that should be made public from a DSO
 // (like in libc++). For cases like these, we can make the vtable hidden or
-// private and create a public alias with the same visibility and linkage as
+// internal and create a public alias with the same visibility and linkage as
 // the original vtable type.
 void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
                                                  llvm::StringRef AliasNameRef) {
@@ -1050,15 +1050,18 @@ void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
   VTableAlias->setVisibility(VTable->getVisibility());
   VTableAlias->setUnnamedAddr(VTable->getUnnamedAddr());
 
-  // Both of these imply dso_local for the vtable.
+  // Both of these will now imply dso_local for the vtable.
   if (!VTable->hasComdat()) {
-    // If this is in a comdat, then we shouldn't make the linkage private due to
-    // an issue in lld where private symbols can be used as the key symbol when
-    // choosing the prevelant group. This leads to "relocation refers to a
-    // symbol in a discarded section".
-    VTable->setLinkage(llvm::GlobalValue::PrivateLinkage);
+    VTable->setLinkage(llvm::GlobalValue::InternalLinkage);
   } else {
-    // We should at least make this hidden since we don't want to expose it.
+    // If a relocation targets an internal linkage symbol, MC will generate the
+    // relocation against the symbol's section instead of the symbol itself
+    // (see ELFObjectWriter::shouldRelocateWithSymbol). If an internal symbol is
+    // in a COMDAT section group, that section might be discarded, and then the
+    // relocation to that section will generate a linker error. We therefore
+    // make COMDAT vtables hidden instead of internal: they'll still not be
+    // public, but relocations will reference the symbol instead of the section
+    // and COMDAT deduplication will thus work as expected.
     VTable->setVisibility(llvm::GlobalValue::HiddenVisibility);
   }
 

clang/test/CodeGenCXX/OmitRTTIComponentABI/simple-vtable-definition.cpp

@@ -11,7 +11,7 @@
 ///
 /// Now vtables should have just two components.
 // POINTER: @_ZTV1A = unnamed_addr constant { [2 x ptr] } { [2 x ptr] [ptr null, ptr @_ZN1A3fooEv] }, align 8
-// RELATIVE: @_ZTV1A.local = private unnamed_addr constant { [2 x i32] } { [2 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [2 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 1) to i64)) to i32)] }, align 4
+// RELATIVE: @_ZTV1A.local = internal unnamed_addr constant { [2 x i32] } { [2 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [2 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 1) to i64)) to i32)] }, align 4
 // RELATIVE: @_ZTV1A = unnamed_addr alias { [2 x i32] }, ptr @_ZTV1A.local
 
 /// None of these supplementary symbols should be emitted with -fno-rtti, but

clang/test/CodeGenCXX/RelativeVTablesABI/child-inheritted-from-parent-in-comdat.cpp

@@ -13,7 +13,7 @@
 // CHECK: $_ZTI1A.rtti_proxy = comdat any
 
 // The VTable for B is emitted here since it has a key function which is defined in this module
-// CHECK: @_ZTV1B.local = private unnamed_addr constant { [3 x i32] } { [3 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
+// CHECK: @_ZTV1B.local = internal unnamed_addr constant { [3 x i32] } { [3 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
 
 // The VTable for A is emitted here and in a comdat section since it has no key function, and is used in this module when creating an instance of A (in func()).
 // CHECK: @_ZTV1A.local = linkonce_odr hidden unnamed_addr constant { [3 x i32] } { [3 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1A.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [3 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, comdat($_ZTV1A), align 4

clang/test/CodeGenCXX/RelativeVTablesABI/cross-translation-unit-1.cpp

@@ -7,7 +7,7 @@
 
 // CHECK: $_ZTI1A.rtti_proxy = comdat any
 
-// CHECK: @_ZTV1A.local = private unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1A.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3barEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
+// CHECK: @_ZTV1A.local = internal unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1A.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3barEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1A.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
 // @_ZTV1A ={{.*}} unnamed_addr alias { [4 x i32] }, ptr @_ZTV1A.local
 
 void A::foo() {}

clang/test/CodeGenCXX/RelativeVTablesABI/cross-translation-unit-2.cpp

@@ -7,7 +7,7 @@
 
 // CHECK: $_ZTI1B.rtti_proxy = comdat any
 
-// CHECK: @_ZTV1B.local = private unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3barEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
+// CHECK: @_ZTV1B.local = internal unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3barEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
 // CHECK: @_ZTV1B ={{.*}} unnamed_addr alias { [4 x i32] }, ptr @_ZTV1B.local
 
 // A::bar() is defined outside of the module that defines the vtable for A

clang/test/CodeGenCXX/RelativeVTablesABI/diamond-inheritance.cpp

@@ -4,16 +4,16 @@
 // RUN: %clang_cc1 %s -triple=aarch64-unknown-fuchsia -O1 -o - -emit-llvm -fhalf-no-semantic-interposition | FileCheck %s
 
 // VTable for B should contain offset to top (0), RTTI pointer, A::foo(), and B::barB().
-// CHECK: @_ZTV1B.local = private unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B4barBEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
+// CHECK: @_ZTV1B.local = internal unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1B.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B4barBEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1B.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
 
 // VTable for C should contain offset to top (0), RTTI pointer, A::foo(), and C::barC().
-// CHECK: @_ZTV1C.local = private unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1C.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1C.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1C.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1C4barCEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1C.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
+// CHECK: @_ZTV1C.local = internal unnamed_addr constant { [4 x i32] } { [4 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1C.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1C.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1A3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1C.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1C4barCEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [4 x i32] }, ptr @_ZTV1C.local, i32 0, i32 0, i32 2) to i64)) to i32)] }, align 4
 
 // VTable for D should be similar to the mutiple inheritance example where this
 // vtable contains 2 inner vtables:
 // - 1st table containing D::foo(), B::barB(), and D::baz().
 // - 2nd table containing a thunk to D::foo() and C::barC().
-// CHECK: @_ZTV1D.local = private unnamed_addr constant { [5 x i32], [4 x i32] } { [5 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1D.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1D3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B4barBEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1D3bazEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32)], [4 x i32] [i32 -8, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1D.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 1, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZThn8_N1D3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 1, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1C4barCEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 1, i32 2) to i64)) to i32)] }, align 4
+// CHECK: @_ZTV1D.local = internal unnamed_addr constant { [5 x i32], [4 x i32] } { [5 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1D.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1D3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1B4barBEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1D3bazEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 0, i32 2) to i64)) to i32)], [4 x i32] [i32 -8, i32 trunc (i64 sub (i64 ptrtoint (ptr @_ZTI1D.rtti_proxy to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 1, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZThn8_N1D3fooEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 1, i32 2) to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint (ptr dso_local_equivalent @_ZN1C4barCEv to i64), i64 ptrtoint (ptr getelementptr inbounds ({ [5 x i32], [4 x i32] }, ptr @_ZTV1D.local, i32 0, i32 1, i32 2) to i64)) to i32)] }, align 4
 
 // @_ZTV1B ={{.*}} unnamed_addr alias { [4 x i32] }, ptr @_ZTV1B.local
 // @_ZTV1C ={{.*}} unnamed_addr alias { [4 x i32] }, ptr @_ZTV1C.local