[PR32482] Fix bitfield layout for -mms-bitfield and pragma pack

The patch ensures that a new storage unit is created when the new bitfield's
size is wider than the available bits.

rdar://36343145

Differential Revision: https://reviews.llvm.org/D42660

llvm-svn: 323921

1 files changed, 4 insertions, 3 deletions

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index a9d43dfa80c..dddacf2a5fe 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1504,9 +1504,10 @@ void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
     FieldAlign = TypeSize;
 
     // If the previous field was not a bitfield, or was a bitfield
-    // with a different storage unit size, we're done with that
-    // storage unit.
-    if (LastBitfieldTypeSize != TypeSize) {
+    // with a different storage unit size, or if this field doesn't fit into
+    // the current storage unit, we're done with that storage unit.
+    if (LastBitfieldTypeSize != TypeSize ||
+        UnfilledBitsInLastUnit < FieldSize) {
       // Also, ignore zero-length bitfields after non-bitfields.
       if (!LastBitfieldTypeSize && !FieldSize)
         FieldAlign = 1;