1 files changed, 9 insertions, 2 deletions
diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index a10d8e791b0..06192bd2eea 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -377,6 +377,10 @@ CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
     }
     return;
   }
+
+  llvm::Type *WordType =
+      DataLayout.getLargestLegalIntType(Types.getLLVMContext());
+  uint64_t WordSize = WordType ? DataLayout.getTypeSizeInBits(WordType) : 0;
   for (;;) {
     // Check to see if we need to start a new run.
     if (Run == FieldEnd) {
@@ -392,9 +396,12 @@ CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
       ++Field;
       continue;
     }
-    // Add bitfields to the run as long as they qualify.
+    // Add bitfields to the run as long as they qualify. If we end up on a word
+    // boundary we insert a break since it's equivalent and very wide types are
+    // harder to optimize with.
     if (Field != FieldEnd && Field->getBitWidthValue(Context) != 0 &&
-        Tail == getFieldBitOffset(*Field)) {
+        Tail == getFieldBitOffset(*Field) &&
+        WordSize != Tail - StartBitOffset) {
       Tail += Field->getBitWidthValue(Context);
       ++Field;
       continue;