[Clang] Fix crash when checking misaligned member with dependent type

[junaire]

Summary

If the type is dependent, we should just discard it and not checking its
alignment as it doesn't exisit yet.
Fixes https://github.com/llvm/llvm-project/issues/58370

[aaron.ballman]

clang/lib/Sema/SemaChecking.cpp

17397

We don't typically use top-level const qualification.

17398–17399

Hmm, is this logic correct? Don't we want:

T->isDependentType() ||
  (T->isPointerType() &&
    (T->getPointeeType()->isIncompleteType() || Context.getTypeAlignInChars(T->getPointeeType()) <= MA->Alignment))

[junaire]

Address Aaron's comments, thanks!

[shafik]

clang/lib/Sema/SemaChecking.cpp

17398–17399

Why did you drop the T->isIntegerType()?

clang/test/SemaCXX/misaligned-member-with-depdent-type.cpp

5

I think since the bug report had malformed code, it would be worth it to include that case as well.

[aaron.ballman]

clang/lib/Sema/SemaChecking.cpp

17398–17399

Whoops! That's totally a typo on my part, I didn't intend to drop it.

[junaire]

Add the original mailformed test case, thanks Shafik!

[junaire]

clang/lib/Sema/SemaChecking.cpp

17398–17399

Why did you drop the T->isIntegerType()?

There may be some misunderstanding here. So previously I hoist the pointer-related checks and put T->isDependentType() into it. After Aaron's words, I realized it was wrong so I changed the whole check condition to is T an integer type? || is T a dependent type ?|| is T a pointer type and other constraints (put them on the same level)

That said you're looking at the old diff so there's nothing need to worried about :)

[aaron.ballman]

LGTM!

clang/lib/Sema/SemaChecking.cpp

 void Sema::DiscardMisalignedMemberAddress(const Type *T, Expr *E) {
   E = E->IgnoreParens();
   if (!T->isPointerType() && !T->isIntegerType())
     return;
   if (isa<UnaryOperator>(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));
+      auto *MA = llvm::find(MisalignedMembers, MisalignedMember(Op));
+      const bool IsDiscardMisalignedPointer =
+          T->isPointerType() &&
+          (T->getPointeeType()->isIncompleteType() || T->isDependentType() ||
+           Context.getTypeAlignInChars(T->getPointeeType()) <= MA->Alignment);
       if (MA != MisalignedMembers.end() &&
-          (T->isIntegerType() ||
-           (T->isPointerType() && (T->getPointeeType()->isIncompleteType() ||
-                                   Context.getTypeAlignInChars(
-                                       T->getPointeeType()) <= MA->Alignment))))
+          (T->isIntegerType() || IsDiscardMisalignedPointer))
         MisalignedMembers.erase(MA);
     }
   }
 }
 
 void Sema::RefersToMemberWithReducedAlignment(
     Expr *E,
     llvm::function_ref<void(Expr *, RecordDecl *, FieldDecl *, CharUnits)>

clang/test/SemaCXX/misaligned-member-with-depdent-type.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+struct __attribute__((packed)) {
+  unsigned options;
+  template <typename T>
+  void getOptions() {
+      (T *)&options;
+  }
+} s;