[clang][bytecode] Save a per-Block IsWeak bit (llvm#111248)

Checking the decl for every load is rather expensive.

Author: tbaederr

clang/lib/AST/ByteCode/InterpBlock.cpp

@@ -100,8 +100,8 @@ bool Block::hasPointer(const Pointer *P) const {
 #endif
 
 DeadBlock::DeadBlock(DeadBlock *&Root, Block *Blk)
-    : Root(Root),
-      B(~0u, Blk->Desc, Blk->IsStatic, Blk->IsExtern, /*isDead=*/true) {
+    : Root(Root), B(~0u, Blk->Desc, Blk->IsStatic, Blk->IsExtern, Blk->IsWeak,
+                    /*isDead=*/true) {
   // Add the block to the chain of dead blocks.
   if (Root)
     Root->Prev = this;

clang/lib/AST/ByteCode/InterpBlock.h

@@ -50,16 +50,17 @@ class Block final {
 public:
   /// Creates a new block.
   Block(unsigned EvalID, const std::optional<unsigned> &DeclID,
-        const Descriptor *Desc, bool IsStatic = false, bool IsExtern = false)
+        const Descriptor *Desc, bool IsStatic = false, bool IsExtern = false,
+        bool IsWeak = false)
       : EvalID(EvalID), DeclID(DeclID), IsStatic(IsStatic), IsExtern(IsExtern),
-        IsDynamic(false), Desc(Desc) {
+        IsDynamic(false), IsWeak(IsWeak), Desc(Desc) {
     assert(Desc);
   }
 
   Block(unsigned EvalID, const Descriptor *Desc, bool IsStatic = false,
-        bool IsExtern = false)
+        bool IsExtern = false, bool IsWeak = false)
       : EvalID(EvalID), DeclID((unsigned)-1), IsStatic(IsStatic),
-        IsExtern(IsExtern), IsDynamic(false), Desc(Desc) {
+        IsExtern(IsExtern), IsDynamic(false), IsWeak(IsWeak), Desc(Desc) {
     assert(Desc);
   }
 
@@ -73,6 +74,7 @@ class Block final {
   bool isStatic() const { return IsStatic; }
   /// Checks if the block is temporary.
   bool isTemporary() const { return Desc->IsTemporary; }
+  bool isWeak() const { return IsWeak; }
   bool isDynamic() const { return IsDynamic; }
   /// Returns the size of the block.
   unsigned getSize() const { return Desc->getAllocSize(); }
@@ -135,9 +137,9 @@ class Block final {
   friend class DynamicAllocator;
 
   Block(unsigned EvalID, const Descriptor *Desc, bool IsExtern, bool IsStatic,
-        bool IsDead)
+        bool IsWeak, bool IsDead)
       : EvalID(EvalID), IsStatic(IsStatic), IsExtern(IsExtern), IsDead(true),
-        IsDynamic(false), Desc(Desc) {
+        IsDynamic(false), IsWeak(IsWeak), Desc(Desc) {
     assert(Desc);
   }
 
@@ -170,6 +172,7 @@ class Block final {
   /// Flag indicating if this block has been allocated via dynamic
   /// memory allocation (e.g. malloc).
   bool IsDynamic = false;
+  bool IsWeak = false;
   /// Pointer to the stack slot descriptor.
   const Descriptor *Desc;
 };

clang/lib/AST/ByteCode/Pointer.h

@@ -524,9 +524,7 @@ class Pointer {
       return false;
 
     assert(isBlockPointer());
-    if (const ValueDecl *VD = getDeclDesc()->asValueDecl())
-      return VD->isWeak();
-    return false;
+    return asBlockPointer().Pointee->isWeak();
   }
   /// Checks if an object was initialized.
   bool isInitialized() const;

clang/lib/AST/ByteCode/Program.cpp

@@ -152,10 +152,12 @@ std::optional<unsigned> Program::getOrCreateDummy(const DeclTy &D) {
     return It->second;
 
   QualType QT;
+  bool IsWeak = false;
   if (const auto *E = D.dyn_cast<const Expr *>()) {
     QT = E->getType();
   } else {
     const ValueDecl *VD = cast<ValueDecl>(D.get<const Decl *>());
+    IsWeak = VD->isWeak();
     QT = VD->getType();
     if (const auto *RT = QT->getAs<ReferenceType>())
       QT = RT->getPointeeType();
@@ -182,7 +184,7 @@ std::optional<unsigned> Program::getOrCreateDummy(const DeclTy &D) {
 
   auto *G = new (Allocator, Desc->getAllocSize())
       Global(Ctx.getEvalID(), getCurrentDecl(), Desc, /*IsStatic=*/true,
-             /*IsExtern=*/false);
+             /*IsExtern=*/false, IsWeak);
   G->block()->invokeCtor();
 
   Globals.push_back(G);
@@ -193,6 +195,7 @@ std::optional<unsigned> Program::getOrCreateDummy(const DeclTy &D) {
 std::optional<unsigned> Program::createGlobal(const ValueDecl *VD,
                                               const Expr *Init) {
   bool IsStatic, IsExtern;
+  bool IsWeak = VD->isWeak();
   if (const auto *Var = dyn_cast<VarDecl>(VD)) {
     IsStatic = Context::shouldBeGloballyIndexed(VD);
     IsExtern = Var->hasExternalStorage();
@@ -207,7 +210,8 @@ 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, Init)) {
+  if (auto Idx =
+          createGlobal(VD, VD->getType(), IsStatic, IsExtern, IsWeak, Init)) {
     for (const Decl *P = VD; P; P = P->getPreviousDecl()) {
       if (P != VD) {
         unsigned PIdx = GlobalIndices[P];
@@ -225,7 +229,7 @@ std::optional<unsigned> Program::createGlobal(const Expr *E) {
   if (auto Idx = getGlobal(E))
     return Idx;
   if (auto Idx = createGlobal(E, E->getType(), /*isStatic=*/true,
-                              /*isExtern=*/false)) {
+                              /*isExtern=*/false, /*IsWeak=*/false)) {
     GlobalIndices[E] = *Idx;
     return *Idx;
   }
@@ -234,7 +238,7 @@ std::optional<unsigned> Program::createGlobal(const Expr *E) {
 
 std::optional<unsigned> Program::createGlobal(const DeclTy &D, QualType Ty,
                                               bool IsStatic, bool IsExtern,
-                                              const Expr *Init) {
+                                              bool IsWeak, const Expr *Init) {
   // Create a descriptor for the global.
   Descriptor *Desc;
   const bool IsConst = Ty.isConstQualified();
@@ -251,8 +255,8 @@ std::optional<unsigned> Program::createGlobal(const DeclTy &D, QualType Ty,
   // Allocate a block for storage.
   unsigned I = Globals.size();
 
-  auto *G = new (Allocator, Desc->getAllocSize())
-      Global(Ctx.getEvalID(), getCurrentDecl(), Desc, IsStatic, IsExtern);
+  auto *G = new (Allocator, Desc->getAllocSize()) Global(
+      Ctx.getEvalID(), getCurrentDecl(), Desc, IsStatic, IsExtern, IsWeak);
   G->block()->invokeCtor();
 
   // Initialize InlineDescriptor fields.

clang/lib/AST/ByteCode/Program.h

@@ -152,7 +152,7 @@ class Program final {
 
   std::optional<unsigned> createGlobal(const DeclTy &D, QualType Ty,
                                        bool IsStatic, bool IsExtern,
-                                       const Expr *Init = nullptr);
+                                       bool IsWeak, const Expr *Init = nullptr);
 
   /// Reference to the VM context.
   Context &Ctx;