[clang][bytecode] Move pointers from extern globals to new decls (#154273)

Author: tbaederr

clang/lib/AST/ByteCode/InterpBlock.h

@@ -149,6 +149,7 @@ class Block final {
   friend class DeadBlock;
   friend class InterpState;
   friend class DynamicAllocator;
+  friend class Program;
 
   Block(unsigned EvalID, const Descriptor *Desc, bool IsExtern, bool IsStatic,
         bool IsWeak, bool IsDummy, bool IsDead)

clang/lib/AST/ByteCode/Pointer.h

@@ -804,6 +804,7 @@ class Pointer {
   friend class InterpState;
   friend struct InitMap;
   friend class DynamicAllocator;
+  friend class Program;
 
   /// Returns the embedded descriptor preceding a field.
   InlineDescriptor *getInlineDesc() const {

clang/lib/AST/ByteCode/Program.cpp

@@ -213,19 +213,32 @@ std::optional<unsigned> Program::createGlobal(const ValueDecl *VD,
 
   // Register all previous declarations as well. For extern blocks, just replace
   // the index with the new variable.
-  if (auto Idx =
-          createGlobal(VD, VD->getType(), IsStatic, IsExtern, IsWeak, Init)) {
-    for (const Decl *P = VD; P; P = P->getPreviousDecl()) {
-      unsigned &PIdx = GlobalIndices[P];
-      if (P != VD) {
-        if (Globals[PIdx]->block()->isExtern())
-          Globals[PIdx] = Globals[*Idx];
+  std::optional<unsigned> Idx =
+      createGlobal(VD, VD->getType(), IsStatic, IsExtern, IsWeak, Init);
+  if (!Idx)
+    return std::nullopt;
+
+  Global *NewGlobal = Globals[*Idx];
+  for (const Decl *Redecl : VD->redecls()) {
+    unsigned &PIdx = GlobalIndices[Redecl];
+    if (Redecl != VD) {
+      if (Block *RedeclBlock = Globals[PIdx]->block();
+          RedeclBlock->isExtern()) {
+        Globals[PIdx] = NewGlobal;
+        // All pointers pointing to the previous extern decl now point to the
+        // new decl.
+        for (Pointer *Ptr = RedeclBlock->Pointers; Ptr;
+             Ptr = Ptr->PointeeStorage.BS.Next) {
+          RedeclBlock->removePointer(Ptr);
+          Ptr->PointeeStorage.BS.Pointee = NewGlobal->block();
+          NewGlobal->block()->addPointer(Ptr);
+        }
       }
-      PIdx = *Idx;
     }
-    return *Idx;
+    PIdx = *Idx;
   }
-  return std::nullopt;
+
+  return *Idx;
 }
 
 std::optional<unsigned> Program::createGlobal(const Expr *E) {
@@ -264,7 +277,7 @@ std::optional<unsigned> Program::createGlobal(const DeclTy &D, QualType Ty,
       Ctx.getEvalID(), getCurrentDecl(), Desc, IsStatic, IsExtern, IsWeak);
   G->block()->invokeCtor();
 
-  // Initialize InlineDescriptor fields.
+  // Initialize GlobalInlineDescriptor fields.
   auto *GD = new (G->block()->rawData()) GlobalInlineDescriptor();
   if (!Init)
     GD->InitState = GlobalInitState::NoInitializer;

clang/test/AST/ByteCode/literals.cpp

@@ -1428,3 +1428,10 @@ namespace OnePastEndCmp {
   constexpr const int *q = &s.a + 1;
   static_assert(p != q, "");
 }
+
+namespace ExternRedecl {
+  extern const int a;
+  constexpr const int *p = &a;
+  constexpr int a = 10;
+  static_assert(*p == 10, "");
+}