[clang][CodeGen] Switch declaration of vtable information to be [0 x ptr] (#65596)

nunoplopes · web-flow · commit 8a2d68f6be50 · 2023-09-09T07:50:35.000+01:00
Continuing the discussion in https://discourse.llvm.org/t/codegen-layout-of-si-class-type-info-doesnt-match-the-actual-size/73274 Before we had this code: @_ZTVN10__cxxabiv117__class_type_infoE = external global ptr now we'll produce: @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr] This is because we may not know the exact size of this data, and clang issues gep inbounds with idx=2. Before, that gep would always result in poison.
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -3669,9 +3669,10 @@ void ItaniumRTTIBuilder::BuildVTablePointer(const Type *Ty) {
   // Check if the alias exists. If it doesn't, then get or create the global.
   if (CGM.getItaniumVTableContext().isRelativeLayout())
     VTable = CGM.getModule().getNamedAlias(VTableName);
-  if (!VTable)
-    VTable =
-        CGM.getModule().getOrInsertGlobal(VTableName, CGM.GlobalsInt8PtrTy);
+  if (!VTable) {
+    llvm::Type *Ty = llvm::ArrayType::get(CGM.GlobalsInt8PtrTy, 0);
+    VTable = CGM.getModule().getOrInsertGlobal(VTableName, Ty);
+  }
 
   CGM.setDSOLocal(cast<llvm::GlobalValue>(VTable->stripPointerCasts()));
 
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/child-vtable-in-comdat.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/child-vtable-in-comdat.cpp
@@ -14,7 +14,7 @@
 // CHECK-DAG: @_ZTV1B.local = linkonce_odr hidden 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)] }, comdat($_ZTV1B), align 4
 
 // The RTTI objects aren’t that important, but it is good to know that they are emitted here since they are used in the vtable for B, and external references are used for RTTI stuff from A.
-// CHECK-DAG: @_ZTVN10__cxxabiv120__si_class_type_infoE = external global ptr
+// CHECK-DAG: @_ZTVN10__cxxabiv120__si_class_type_infoE = external global [0 x ptr]
 // CHECK-DAG: @_ZTS1B =
 // CHECK-DAG: @_ZTI1A =
 // CHECK-DAG: @_ZTI1B =
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/parent-vtable-in-comdat.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/parent-vtable-in-comdat.cpp
@@ -15,7 +15,7 @@
 
 // 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.
 // 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
-// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external global ptr
+// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr]
 // CHECK: @_ZTS1A = linkonce_odr constant [3 x i8] c"1A\00", comdat, align 1
 // CHECK: @_ZTI1A = linkonce_odr constant { ptr, ptr } { ptr getelementptr inbounds (i8, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i32 8), ptr @_ZTS1A }, comdat, align 8
 // CHECK: @_ZTI1A.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1A, comdat
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/simple-vtable-definition.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/simple-vtable-definition.cpp
@@ -9,7 +9,7 @@
 // The vtable definition itself is private so we can take relative references to
 // it. The vtable symbol will be exposed through a public alias.
 // CHECK: @_ZTV1A.local = private 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)] }, align 4
-// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external global ptr
+// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr]
 // CHECK: @_ZTS1A ={{.*}} constant [3 x i8] c"1A\00", align 1
 // CHECK: @_ZTI1A ={{.*}} constant { ptr, ptr } { ptr getelementptr inbounds (i8, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i32 8), ptr @_ZTS1A }, align 8
 
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/type-info.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/type-info.cpp
@@ -7,10 +7,10 @@
 // CHECK: $_ZTI1A.rtti_proxy = comdat any
 // CHECK: $_ZTI1B.rtti_proxy = comdat any
 
-// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external global ptr
+// CHECK: @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr]
 // CHECK: @_ZTS1A ={{.*}} constant [3 x i8] c"1A\00", align 1
 // CHECK: @_ZTI1A ={{.*}} constant { ptr, ptr } { ptr getelementptr inbounds (i8, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i32 8), ptr @_ZTS1A }, align 8
-// CHECK: @_ZTVN10__cxxabiv120__si_class_type_infoE = external global ptr
+// CHECK: @_ZTVN10__cxxabiv120__si_class_type_infoE = external global [0 x ptr]
 // CHECK: @_ZTS1B ={{.*}} constant [3 x i8] c"1B\00", align 1
 // CHECK: @_ZTI1B ={{.*}} constant { ptr, ptr, ptr } { ptr getelementptr inbounds (i8, ptr @_ZTVN10__cxxabiv120__si_class_type_infoE, i32 8), ptr @_ZTS1B, ptr @_ZTI1A }, align 8
 // CHECK: @_ZTI1A.rtti_proxy = hidden unnamed_addr constant ptr @_ZTI1A, comdat
diff --git a/clang/test/CodeGenCXX/typeinfo-with-address-space.cpp b/clang/test/CodeGenCXX/typeinfo-with-address-space.cpp
@@ -14,8 +14,8 @@ class B : A {
 // NO-AS: @_ZTISt9type_info = external constant ptr
 // AS: @_ZTIi = external addrspace(1) constant ptr addrspace(1)
 // NO-AS: @_ZTIi = external constant ptr
-// AS: @_ZTVN10__cxxabiv117__class_type_infoE = external addrspace(1) global ptr addrspace(1)
-// NO-AS: @_ZTVN10__cxxabiv117__class_type_infoE = external global ptr
+// AS: @_ZTVN10__cxxabiv117__class_type_infoE = external addrspace(1) global [0 x ptr addrspace(1)]
+// NO-AS: @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr]
 // AS: @_ZTS1A = linkonce_odr addrspace(1) constant [3 x i8] c"1A\00", comdat, align 1
 // NO-AS: @_ZTS1A = linkonce_odr constant [3 x i8] c"1A\00", comdat, align 1
 // AS: @_ZTI1A = linkonce_odr addrspace(1) constant { ptr addrspace(1), ptr addrspace(1) } { ptr addrspace(1) getelementptr inbounds (ptr addrspace(1), ptr addrspace(1) @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), ptr addrspace(1) @_ZTS1A }, comdat, align 8
