[Sema] Fix false positive warnings for misaligned member access

clang/docs/ReleaseNotes.rst

@@ -166,6 +166,10 @@ Improvements to Clang's diagnostics
   "signedness of format specifier 'u' is incompatible with 'c' [-Wformat-signedness]"
   and the API-visible diagnostic id will be appropriate.
 
+- Fixed false positives in ``-Waddress-of-packed-member`` diagnostics when
+  potential misaligned members get processed before they can get discarded.
+  (#GH144729)
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Sema/Sema.h

@@ -2659,9 +2659,9 @@ class Sema final : public SemaBase {
   /// identifies the magic value.
   typedef std::pair<const IdentifierInfo *, uint64_t> TypeTagMagicValue;
 
-  /// Diagnoses the current set of gathered accesses. This typically
-  /// happens at full expression level. The set is cleared after emitting the
-  /// diagnostics.
+  /// Diagnoses the current set of gathered accesses. This happens at the end of
+  /// each expression evaluation context. Diagnostics are emitted only for
+  /// accesses gathered in the current evaluation context.
   void DiagnoseMisalignedMembers();
 
   /// This function checks if the expression is in the sef of potentially
@@ -3117,9 +3117,6 @@ class Sema final : public SemaBase {
 
     bool operator==(const MisalignedMember &m) { return this->E == m.E; }
   };
-  /// Small set of gathered accesses to potentially misaligned members
-  /// due to the packed attribute.
-  SmallVector<MisalignedMember, 4> MisalignedMembers;
 
   /// Adds an expression to the set of gathered misaligned members.
   void AddPotentialMisalignedMembers(Expr *E, RecordDecl *RD, ValueDecl *MD,
@@ -6765,6 +6762,10 @@ class Sema final : public SemaBase {
     /// InLifetimeExtendingContext is true.
     SmallVector<MaterializeTemporaryExpr *, 8> ForRangeLifetimeExtendTemps;
 
+    /// Small set of gathered accesses to potentially misaligned members
+    /// due to the packed attribute.
+    SmallVector<MisalignedMember, 4> MisalignedMembers;
+
     /// \brief Describes whether we are in an expression constext which we have
     /// to handle differently.
     enum ExpressionKind {

clang/lib/Sema/SemaChecking.cpp

@@ -14125,7 +14125,6 @@ void Sema::CheckCompletedExpr(Expr *E, SourceLocation CheckLoc,
     CheckUnsequencedOperations(E);
   if (!IsConstexpr && !E->isValueDependent())
     CheckForIntOverflow(E);
-  DiagnoseMisalignedMembers();
 }
 
 void Sema::CheckBitFieldInitialization(SourceLocation InitLoc,
@@ -15570,11 +15569,12 @@ void Sema::CheckArgumentWithTypeTag(const ArgumentWithTypeTagAttr *Attr,
 
 void Sema::AddPotentialMisalignedMembers(Expr *E, RecordDecl *RD, ValueDecl *MD,
                                          CharUnits Alignment) {
-  MisalignedMembers.emplace_back(E, RD, MD, Alignment);
+  currentEvaluationContext().MisalignedMembers.emplace_back(E, RD, MD,
+                                                            Alignment);
 }
 
 void Sema::DiagnoseMisalignedMembers() {
-  for (MisalignedMember &m : MisalignedMembers) {
+  for (MisalignedMember &m : currentEvaluationContext().MisalignedMembers) {
     const NamedDecl *ND = m.RD;
     if (ND->getName().empty()) {
       if (const TypedefNameDecl *TD = m.RD->getTypedefNameForAnonDecl())
@@ -15583,7 +15583,7 @@ void Sema::DiagnoseMisalignedMembers() {
     Diag(m.E->getBeginLoc(), diag::warn_taking_address_of_packed_member)
         << m.MD << ND << m.E->getSourceRange();
   }
-  MisalignedMembers.clear();
+  currentEvaluationContext().MisalignedMembers.clear();
 }
 
 void Sema::DiscardMisalignedMemberAddress(const Type *T, Expr *E) {
@@ -15594,13 +15594,15 @@ void Sema::DiscardMisalignedMemberAddress(const Type *T, Expr *E) {
       cast<UnaryOperator>(E)->getOpcode() == UO_AddrOf) {
     auto *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
     if (isa<MemberExpr>(Op)) {
-      auto *MA = llvm::find(MisalignedMembers, MisalignedMember(Op));
-      if (MA != MisalignedMembers.end() &&
+      auto &MisalignedMembersForExpr =
+          currentEvaluationContext().MisalignedMembers;
+      auto *MA = llvm::find(MisalignedMembersForExpr, MisalignedMember(Op));
+      if (MA != MisalignedMembersForExpr.end() &&
           (T->isDependentType() || T->isIntegerType() ||
            (T->isPointerType() && (T->getPointeeType()->isIncompleteType() ||
                                    Context.getTypeAlignInChars(
                                        T->getPointeeType()) <= MA->Alignment))))
-        MisalignedMembers.erase(MA);
+        MisalignedMembersForExpr.erase(MA);
     }
   }
 }

clang/lib/Sema/SemaExpr.cpp

@@ -18121,6 +18121,8 @@ void Sema::PopExpressionEvaluationContext() {
     MaybeODRUseExprs.insert_range(Rec.SavedMaybeODRUseExprs);
   }
 
+  DiagnoseMisalignedMembers();
+
   // Pop the current expression evaluation context off the stack.
   ExprEvalContexts.pop_back();
 }

clang/test/Sema/address-packed.c

@@ -338,3 +338,11 @@ struct Invalid0 {
 void *g14(struct Invalid0 *ivl) {
   return &(ivl->x);
 }
+
+void to_void_with_expr(void *ptr, int expr);
+
+void g15(void) {
+  struct Arguable arguable;
+  to_void_with_expr(&arguable.x, 3); // no-warning
+  to_void_with_expr(&arguable.x, ({3;})); // no-warning
+}