[clang][bytecode] Optimize InitElem{,Pop} (#159084)

Try harder to avoid creating a new `Pointer` for the element.

Author: tbaederr

clang/lib/AST/ByteCode/Interp.h

@@ -2127,19 +2127,28 @@ bool InitElem(InterpState &S, CodePtr OpPC, uint32_t Idx) {
   if (Ptr.isUnknownSizeArray())
     return false;
 
+  const Descriptor *Desc = Ptr.getFieldDesc();
   // In the unlikely event that we're initializing the first item of
   // a non-array, skip the atIndex().
-  if (Idx == 0 && !Ptr.getFieldDesc()->isArray()) {
+  if (Idx == 0 && !Desc->isArray()) {
     Ptr.initialize();
     new (&Ptr.deref<T>()) T(Value);
     return true;
   }
 
-  const Pointer &ElemPtr = Ptr.atIndex(Idx);
-  if (!CheckInit(S, OpPC, ElemPtr))
+  if (!CheckLive(S, OpPC, Ptr, AK_Assign))
     return false;
-  ElemPtr.initialize();
-  new (&ElemPtr.deref<T>()) T(Value);
+  if (Idx >= Desc->getNumElems()) {
+    // CheckRange.
+    if (S.getLangOpts().CPlusPlus) {
+      const SourceInfo &Loc = S.Current->getSource(OpPC);
+      S.FFDiag(Loc, diag::note_constexpr_access_past_end)
+          << AK_Assign << S.Current->getRange(OpPC);
+    }
+    return false;
+  }
+  Ptr.initializeElement(Idx);
+  new (&Ptr.elem<T>(Idx)) T(Value);
   return true;
 }
 
@@ -2148,22 +2157,32 @@ template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool InitElemPop(InterpState &S, CodePtr OpPC, uint32_t Idx) {
   const T &Value = S.Stk.pop<T>();
   const Pointer &Ptr = S.Stk.pop<Pointer>();
+
   if (Ptr.isUnknownSizeArray())
     return false;
 
+  const Descriptor *Desc = Ptr.getFieldDesc();
   // In the unlikely event that we're initializing the first item of
   // a non-array, skip the atIndex().
-  if (Idx == 0 && !Ptr.getFieldDesc()->isArray()) {
+  if (Idx == 0 && !Desc->isArray()) {
     Ptr.initialize();
     new (&Ptr.deref<T>()) T(Value);
     return true;
   }
 
-  const Pointer &ElemPtr = Ptr.atIndex(Idx);
-  if (!CheckInit(S, OpPC, ElemPtr))
+  if (!CheckLive(S, OpPC, Ptr, AK_Assign))
     return false;
-  ElemPtr.initialize();
-  new (&ElemPtr.deref<T>()) T(Value);
+  if (Idx >= Desc->getNumElems()) {
+    // CheckRange.
+    if (S.getLangOpts().CPlusPlus) {
+      const SourceInfo &Loc = S.Current->getSource(OpPC);
+      S.FFDiag(Loc, diag::note_constexpr_access_past_end)
+          << AK_Assign << S.Current->getRange(OpPC);
+    }
+    return false;
+  }
+  Ptr.initializeElement(Idx);
+  new (&Ptr.elem<T>(Idx)) T(Value);
   return true;
 }
 

clang/lib/AST/ByteCode/Pointer.cpp

@@ -433,7 +433,8 @@ bool Pointer::isInitialized() const {
   if (!isBlockPointer())
     return true;
 
-  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor)) {
+  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor) &&
+      Offset == BS.Base) {
     const GlobalInlineDescriptor &GD =
         *reinterpret_cast<const GlobalInlineDescriptor *>(block()->rawData());
     return GD.InitState == GlobalInitState::Initialized;
@@ -461,7 +462,8 @@ bool Pointer::isElementInitialized(unsigned Index) const {
   if (isStatic() && BS.Base == 0)
     return true;
 
-  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor)) {
+  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor) &&
+      Offset == BS.Base) {
     const GlobalInlineDescriptor &GD =
         *reinterpret_cast<const GlobalInlineDescriptor *>(block()->rawData());
     return GD.InitState == GlobalInitState::Initialized;
@@ -486,7 +488,8 @@ void Pointer::initialize() const {
 
   assert(BS.Pointee && "Cannot initialize null pointer");
 
-  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor)) {
+  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor) &&
+      Offset == BS.Base) {
     GlobalInlineDescriptor &GD = *reinterpret_cast<GlobalInlineDescriptor *>(
         asBlockPointer().Pointee->rawData());
     GD.InitState = GlobalInitState::Initialized;
@@ -496,35 +499,39 @@ void Pointer::initialize() const {
   const Descriptor *Desc = getFieldDesc();
   assert(Desc);
   if (Desc->isPrimitiveArray()) {
-    // Primitive global arrays don't have an initmap.
-    if (isStatic() && BS.Base == 0)
-      return;
+    if (Desc->getNumElems() != 0)
+      initializeElement(getIndex());
+    return;
+  }
 
-    // Nothing to do for these.
-    if (Desc->getNumElems() == 0)
-      return;
+  // Field has its bit in an inline descriptor.
+  assert(BS.Base != 0 && "Only composite fields can be initialised");
+  getInlineDesc()->IsInitialized = true;
+}
 
-    InitMapPtr &IM = getInitMap();
-    if (!IM)
-      IM =
-          std::make_pair(false, std::make_shared<InitMap>(Desc->getNumElems()));
+void Pointer::initializeElement(unsigned Index) const {
+  // Primitive global arrays don't have an initmap.
+  if (isStatic() && BS.Base == 0)
+    return;
 
-    assert(IM);
+  assert(Index < getFieldDesc()->getNumElems());
 
-    // All initialized.
-    if (IM->first)
-      return;
+  InitMapPtr &IM = getInitMap();
+  if (!IM) {
+    const Descriptor *Desc = getFieldDesc();
+    IM = std::make_pair(false, std::make_shared<InitMap>(Desc->getNumElems()));
+  }
 
-    if (IM->second->initializeElement(getIndex())) {
-      IM->first = true;
-      IM->second.reset();
-    }
+  assert(IM);
+
+  // All initialized.
+  if (IM->first)
     return;
-  }
 
-  // Field has its bit in an inline descriptor.
-  assert(BS.Base != 0 && "Only composite fields can be initialised");
-  getInlineDesc()->IsInitialized = true;
+  if (IM->second->initializeElement(Index)) {
+    IM->first = true;
+    IM->second.reset();
+  }
 }
 
 void Pointer::initializeAllElements() const {
@@ -547,7 +554,8 @@ bool Pointer::allElementsInitialized() const {
   if (isStatic() && BS.Base == 0)
     return true;
 
-  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor)) {
+  if (isRoot() && BS.Base == sizeof(GlobalInlineDescriptor) &&
+      Offset == BS.Base) {
     const GlobalInlineDescriptor &GD =
         *reinterpret_cast<const GlobalInlineDescriptor *>(block()->rawData());
     return GD.InitState == GlobalInitState::Initialized;

clang/lib/AST/ByteCode/Pointer.h

@@ -702,6 +702,8 @@ class Pointer {
 
   /// Initializes a field.
   void initialize() const;
+  /// Initialized the given element of a primitive array.
+  void initializeElement(unsigned Index) const;
   /// Initialize all elements of a primitive array at once. This can be
   /// used in situations where we *know* we have initialized *all* elements
   /// of a primtive array.