[CodeGen] Fix an assertion failure in CGRecordLowering.

This patch fixes a bug in CGRecordLowering::accumulateBitFields where it
unconditionally starts a new run and emits a storage field when it sees
a zero-sized bitfield, which causes an assertion in insertPadding to
fail when -fno-bitfield-type-align is used.

It shouldn't emit new storage if UseZeroLengthBitfieldAlignment and
UseBitFieldTypeAlignment are both false.

rdar://problem/36762205

llvm-svn: 323943

1 files changed, 6 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 1644ab4c072..d794b12b3d3 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -443,14 +443,18 @@ CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field,
 
     // If the start field of a new run is better as a single run, or
     // if current field is better as a single run, or
-    // if current field has zero width bitfield, or
+    // if current field has zero width bitfield and either
+    // UseZeroLengthBitfieldAlignment or UseBitFieldTypeAlignment is set to
+    // true, or
     // if the offset of current field is inconsistent with the offset of
     // previous field plus its offset,
     // skip the block below and go ahead to emit the storage.
     // Otherwise, try to add bitfields to the run.
     if (!StartFieldAsSingleRun && Field != FieldEnd &&
         !IsBetterAsSingleFieldRun(Field) &&
-        Field->getBitWidthValue(Context) != 0 &&
+        (Field->getBitWidthValue(Context) != 0 ||
+         (!Context.getTargetInfo().useZeroLengthBitfieldAlignment() &&
+          !Context.getTargetInfo().useBitFieldTypeAlignment())) &&
         Tail == getFieldBitOffset(*Field)) {
       Tail += Field->getBitWidthValue(Context);
       ++Field;