When diagnosing taking address of packed members skip __unaligned-qualified expressions

[rogfer01]

Summary

Given that we have already explicitly stated in the qualifier that the expression is __unaligned,
it makes little sense to diagnose that the address of the packed member may not be aligned.

[aaron.ballman]

LGTM!

[rogfer01]

Thanks for the review @aaron.ballman!

lib/Sema/SemaChecking.cpp

 void Sema::RefersToMemberWithReducedAlignment(
     Expr *E,
     llvm::function_ref<void(Expr *, RecordDecl *, FieldDecl *, CharUnits)>
         Action) {
   const auto *ME = dyn_cast<MemberExpr>(E);
   if (!ME)
     return;
 
+  // No need to check expressions with an __unaligned-qualified type.
+  if (E->getType().getQualifiers().hasUnaligned())
+    return;
+
   // For a chain of MemberExpr like "a.b.c.d" this list
   // will keep FieldDecl's like [d, c, b].
   SmallVector<FieldDecl *, 4> ReverseMemberChain;
   const MemberExpr *TopME = nullptr;
   bool AnyIsPacked = false;
   do {
     QualType BaseType = ME->getBase()->getType();
     if (ME->isArrow())

test/Sema/address-unaligned.c

+// RUN: %clang_cc1 -fsyntax-only -fms-extensions -verify %s
+// expected-no-diagnostics
+
+typedef
+struct __attribute__((packed)) S1 {
+  char c0;
+  int x;
+  char c1;
+} S1;
+
+void bar(__unaligned int *);
+
+void foo(__unaligned S1* s1)
+{
+    bar(&s1->x);
+}