Ignore pointers to incomplete types when diagnosing misaligned addresses

[rogfer01]

Summary

This is a fix for PR35509 in which we crash because we attempt to compute the alignment of an incomplete type.

[aaron.ballman]

LGTM, thank you!

lib/Sema/SemaChecking.cpp

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

test/SemaCXX/address-packed.cpp

void g1() {
   s1.get(); // expected-note {{in instantiation of member function 'S<int>::get'}}
 
   S<char> s2;
   s2.get();
 
   S<float> s3;
   s3.get(); // expected-note {{in instantiation of member function 'S<float>::get'}}
 }
+
+// PR35509
+typedef long L1;
+struct Incomplete;
+struct S2 {
+  L1 d;
+  Incomplete *e() const;
+} __attribute__((packed));
+Incomplete *S2::e() const { return (Incomplete *)&d; } // no-warning