[clang][ExprConst] Try to minimize emitting unneeded diagnostics

clang/include/clang/AST/Decl.h

@@ -61,6 +61,7 @@ class CompoundStmt;
 class DependentFunctionTemplateSpecializationInfo;
 class EnumDecl;
 class Expr;
+struct EvalStatus;
 class FunctionTemplateDecl;
 class FunctionTemplateSpecializationInfo;
 class FunctionTypeLoc;
@@ -1412,7 +1413,7 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
   APValue *evaluateValue() const;
 
 private:
-  APValue *evaluateValueImpl(SmallVectorImpl<PartialDiagnosticAt> &Notes,
+  APValue *evaluateValueImpl(EvalStatus &EStatus,
                              bool IsConstantInitialization) const;
 
 public:
@@ -1446,7 +1447,7 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
   /// constant initializer. Should only be called once, after completing the
   /// definition of the variable.
   bool checkForConstantInitialization(
-      SmallVectorImpl<PartialDiagnosticAt> &Notes) const;
+      SmallVectorImpl<PartialDiagnosticAt> *Notes) const;
 
   void setInitStyle(InitializationStyle Style) {
     VarDeclBits.InitStyle = Style;

clang/include/clang/AST/Expr.h

@@ -60,6 +60,47 @@ namespace clang {
   class ValueDecl;
   class WarnUnusedResultAttr;
 
+  /// EvalStatus is a struct with detailed info about an evaluation in progress.
+  struct EvalStatus {
+    /// Whether the evaluated expression has side effects.
+    /// For example, (f() && 0) can be folded, but it still has side effects.
+    bool HasSideEffects = false;
+
+    /// Whether the evaluation hit undefined behavior.
+    /// For example, 1.0 / 0.0 can be folded to Inf, but has undefined behavior.
+    /// Likewise, INT_MAX + 1 can be folded to INT_MIN, but has UB.
+    bool HasUndefinedBehavior = false;
+
+    bool HasFFDiagnostic = false;
+    bool HasCCEDiagnostic = false;
+
+    /// Diag - If this is non-null, it will be filled in with a stack of notes
+    /// indicating why evaluation failed (or why it failed to produce a constant
+    /// expression).
+    /// If the expression is unfoldable, the notes will indicate why it's not
+    /// foldable. If the expression is foldable, but not a constant expression,
+    /// the notes will describes why it isn't a constant expression. If the
+    /// expression *is* a constant expression, no notes will be produced.
+    ///
+    /// FIXME: this causes significant performance concerns and should be
+    /// refactored at some point. Not all evaluations of the constant
+    /// expression interpreter will display the given diagnostics, this means
+    /// those kinds of uses are paying the expense of generating a diagnostic
+    /// (which may include expensive operations like converting APValue objects
+    /// to a string representation).
+    SmallVectorImpl<PartialDiagnosticAt> *Diag = nullptr;
+
+    EvalStatus() = default;
+
+    /// Return true if the evaluated expression has
+    /// side effects.
+    bool hasSideEffects() const { return HasSideEffects; }
+
+    bool hasAnyDiagnostic() const {
+      return HasFFDiagnostic || HasCCEDiagnostic;
+    }
+  };
+
 /// A simple array of base specifiers.
 typedef SmallVector<CXXBaseSpecifier*, 4> CXXCastPath;
 
@@ -605,42 +646,6 @@ class Expr : public ValueStmt {
   /// expression is a member pointer constant.
   const ValueDecl *getAsBuiltinConstantDeclRef(const ASTContext &Context) const;
 
-  /// EvalStatus is a struct with detailed info about an evaluation in progress.
-  struct EvalStatus {
-    /// Whether the evaluated expression has side effects.
-    /// For example, (f() && 0) can be folded, but it still has side effects.
-    bool HasSideEffects = false;
-
-    /// Whether the evaluation hit undefined behavior.
-    /// For example, 1.0 / 0.0 can be folded to Inf, but has undefined behavior.
-    /// Likewise, INT_MAX + 1 can be folded to INT_MIN, but has UB.
-    bool HasUndefinedBehavior = false;
-
-    /// Diag - If this is non-null, it will be filled in with a stack of notes
-    /// indicating why evaluation failed (or why it failed to produce a constant
-    /// expression).
-    /// If the expression is unfoldable, the notes will indicate why it's not
-    /// foldable. If the expression is foldable, but not a constant expression,
-    /// the notes will describes why it isn't a constant expression. If the
-    /// expression *is* a constant expression, no notes will be produced.
-    ///
-    /// FIXME: this causes significant performance concerns and should be
-    /// refactored at some point. Not all evaluations of the constant
-    /// expression interpreter will display the given diagnostics, this means
-    /// those kinds of uses are paying the expense of generating a diagnostic
-    /// (which may include expensive operations like converting APValue objects
-    /// to a string representation).
-    SmallVectorImpl<PartialDiagnosticAt> *Diag = nullptr;
-
-    EvalStatus() = default;
-
-    /// Return true if the evaluated expression has
-    /// side effects.
-    bool hasSideEffects() const {
-      return HasSideEffects;
-    }
-  };
-
   /// EvalResult is a struct with detailed info about an evaluated expression.
   struct EvalResult : EvalStatus {
     /// Val - This is the value the expression can be folded to.
@@ -735,8 +740,7 @@ class Expr : public ValueStmt {
   /// can be folded to a constant, and produces any relevant notes. In C++11,
   /// notes will be produced if the expression is not a constant expression.
   bool EvaluateAsInitializer(APValue &Result, const ASTContext &Ctx,
-                             const VarDecl *VD,
-                             SmallVectorImpl<PartialDiagnosticAt> &Notes,
+                             const VarDecl *VD, EvalStatus &Status,
                              bool IsConstantInitializer) const;
 
   /// EvaluateWithSubstitution - Evaluate an expression as if from the context

clang/lib/AST/ByteCode/Compiler.cpp

@@ -6985,8 +6985,8 @@ bool Compiler<Emitter>::visitDeclRef(const ValueDecl *D, const Expr *E) {
       // here -- we will create a global variable in any case, and that
       // will have the state of initializer evaluation attached.
       APValue V;
-      SmallVector<PartialDiagnosticAt> Notes;
-      (void)Init->EvaluateAsInitializer(V, Ctx.getASTContext(), VD, Notes,
+      EvalStatus EStatus;
+      (void)Init->EvaluateAsInitializer(V, Ctx.getASTContext(), VD, EStatus,
                                         true);
       return this->visitDeclRef(D, E);
     }

clang/lib/AST/ByteCode/InterpState.h

@@ -64,9 +64,7 @@ class InterpState final : public State, public SourceMapper {
   const Frame *getBottomFrame() const override { return &BottomFrame; }
 
   // Access objects from the walker context.
-  Expr::EvalStatus &getEvalStatus() const override {
-    return Parent.getEvalStatus();
-  }
+  EvalStatus &getEvalStatus() const override { return Parent.getEvalStatus(); }
   ASTContext &getASTContext() const override { return Ctx.getASTContext(); }
   const LangOptions &getLangOpts() const {
     return Ctx.getASTContext().getLangOpts();

clang/lib/AST/ByteCode/State.cpp

@@ -84,7 +84,12 @@ PartialDiagnostic &State::addDiag(SourceLocation Loc, diag::kind DiagId) {
 
 OptionalDiagnostic State::diag(SourceLocation Loc, diag::kind DiagId,
                                unsigned ExtraNotes, bool IsCCEDiag) {
-  Expr::EvalStatus &EvalStatus = getEvalStatus();
+  EvalStatus &EvalStatus = getEvalStatus();
+  if (IsCCEDiag)
+    EvalStatus.HasCCEDiagnostic = true;
+  else
+    EvalStatus.HasFFDiagnostic = true;
+
   if (EvalStatus.Diag) {
     if (hasPriorDiagnostic()) {
       return OptionalDiagnostic();

clang/lib/AST/ByteCode/State.h

@@ -88,7 +88,7 @@ class State {
   virtual bool hasActiveDiagnostic() = 0;
   virtual void setActiveDiagnostic(bool Flag) = 0;
   virtual void setFoldFailureDiagnostic(bool Flag) = 0;
-  virtual Expr::EvalStatus &getEvalStatus() const = 0;
+  virtual EvalStatus &getEvalStatus() const = 0;
   virtual ASTContext &getASTContext() const = 0;
   virtual bool hasPriorDiagnostic() = 0;
   virtual unsigned getCallStackDepth() = 0;

clang/lib/AST/Decl.cpp

@@ -2573,11 +2573,11 @@ EvaluatedStmt *VarDecl::getEvaluatedStmt() const {
 }
 
 APValue *VarDecl::evaluateValue() const {
-  SmallVector<PartialDiagnosticAt, 8> Notes;
-  return evaluateValueImpl(Notes, hasConstantInitialization());
+  EvalStatus ES;
+  return evaluateValueImpl(ES, hasConstantInitialization());
 }
 
-APValue *VarDecl::evaluateValueImpl(SmallVectorImpl<PartialDiagnosticAt> &Notes,
+APValue *VarDecl::evaluateValueImpl(EvalStatus &EStatus,
                                     bool IsConstantInitialization) const {
   EvaluatedStmt *Eval = ensureEvaluatedStmt();
 
@@ -2598,7 +2598,7 @@ APValue *VarDecl::evaluateValueImpl(SmallVectorImpl<PartialDiagnosticAt> &Notes,
   Eval->IsEvaluating = true;
 
   ASTContext &Ctx = getASTContext();
-  bool Result = Init->EvaluateAsInitializer(Eval->Evaluated, Ctx, this, Notes,
+  bool Result = Init->EvaluateAsInitializer(Eval->Evaluated, Ctx, this, EStatus,
                                             IsConstantInitialization);
 
   // In C++, or in C23 if we're initialising a 'constexpr' variable, this isn't
@@ -2608,7 +2608,7 @@ APValue *VarDecl::evaluateValueImpl(SmallVectorImpl<PartialDiagnosticAt> &Notes,
   if (IsConstantInitialization &&
       (Ctx.getLangOpts().CPlusPlus ||
        (isConstexpr() && Ctx.getLangOpts().C23)) &&
-      !Notes.empty())
+      EStatus.hasAnyDiagnostic())
     Result = false;
 
   // Ensure the computed APValue is cleaned up later if evaluation succeeded,
@@ -2662,7 +2662,7 @@ bool VarDecl::hasConstantInitialization() const {
 }
 
 bool VarDecl::checkForConstantInitialization(
-    SmallVectorImpl<PartialDiagnosticAt> &Notes) const {
+    SmallVectorImpl<PartialDiagnosticAt> *Notes) const {
   EvaluatedStmt *Eval = ensureEvaluatedStmt();
   // If we ask for the value before we know whether we have a constant
   // initializer, we can compute the wrong value (for example, due to
@@ -2676,8 +2676,10 @@ bool VarDecl::checkForConstantInitialization(
   assert(!getInit()->isValueDependent());
 
   // Evaluate the initializer to check whether it's a constant expression.
+  EvalStatus EStatus;
+  EStatus.Diag = Notes;
   Eval->HasConstantInitialization =
-      evaluateValueImpl(Notes, true) && Notes.empty();
+      evaluateValueImpl(EStatus, true) && !EStatus.hasAnyDiagnostic();
 
   // If evaluation as a constant initializer failed, allow re-evaluation as a
   // non-constant initializer if we later find we want the value.