[CodeGen] Fix Bug 47499: __unaligned extension inconsistent behaviour with C and C++

For the language C++ the keyword __unaligned (a Microsoft extension) had no effect on pointers.

The reason, why there was a difference between C and C++ for the keyword __unaligned:
For C, the Method getAsCXXREcordDecl() returns nullptr. That guarantees that hasUnaligned() is called.
If the language is C++, it is not guaranteed, that hasUnaligend() is called and evaluated.

Here are some links:

The Bug: https://bugs.llvm.org/show_bug.cgi?id=47499
Thread on the cfe-dev mailing list: http://lists.llvm.org/pipermail/cfe-dev/2020-September/066783.html
Diff, that introduced the check hasUnaligned() in getNaturalTypeAlignment(): https://reviews.llvm.org/D30166

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D90630

1 files changed, 7 insertions, 6 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 24c0675..ccf5d24 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -6197,16 +6197,17 @@ CharUnits CodeGenModule::getNaturalTypeAlignment(QualType T,
     *BaseInfo = LValueBaseInfo(AlignmentSource::Type);
 
   CharUnits Alignment;
-  // For C++ class pointees, we don't know whether we're pointing at a
-  // base or a complete object, so we generally need to use the
-  // non-virtual alignment.
   const CXXRecordDecl *RD;
-  if (forPointeeType && !AlignForArray && (RD = T->getAsCXXRecordDecl())) {
+  if (T.getQualifiers().hasUnaligned()) {
+    Alignment = CharUnits::One();
+  } else if (forPointeeType && !AlignForArray &&
+             (RD = T->getAsCXXRecordDecl())) {
+    // For C++ class pointees, we don't know whether we're pointing at a
+    // base or a complete object, so we generally need to use the
+    // non-virtual alignment.
     Alignment = getClassPointerAlignment(RD);
   } else {
     Alignment = getContext().getTypeAlignInChars(T);
-    if (T.getQualifiers().hasUnaligned())
-      Alignment = CharUnits::One();
   }
 
   // Cap to the global maximum type alignment unless the alignment