PR18513: make gcc compatible layout for bit-fields with explicit aligned attribute, by Dmitry Polukhin

Fix binary compatibility issue with GCC.
Differential Revision: http://reviews.llvm.org/D14980

llvm-svn: 257462

1 files changed, 9 insertions, 1 deletions

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index bc3c2a831c4..bc5ae0ffc46 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1552,7 +1552,8 @@ void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
     FieldAlign = 1;
 
   // But, if there's an 'aligned' attribute on the field, honor that.
-  if (unsigned ExplicitFieldAlign = D->getMaxAlignment()) {
+  unsigned ExplicitFieldAlign = D->getMaxAlignment();
+  if (ExplicitFieldAlign) {
     FieldAlign = std::max(FieldAlign, ExplicitFieldAlign);
     UnpackedFieldAlign = std::max(UnpackedFieldAlign, ExplicitFieldAlign);
   }
@@ -1601,6 +1602,10 @@ void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
         (AllowPadding &&
          (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)) {
       FieldOffset = llvm::RoundUpToAlignment(FieldOffset, FieldAlign);
+    } else if (ExplicitFieldAlign) {
+      // TODO: figure it out what needs to be done on targets that don't honor
+      // bit-field type alignment like ARM APCS ABI.
+      FieldOffset = llvm::RoundUpToAlignment(FieldOffset, ExplicitFieldAlign);
     }
 
     // Repeat the computation for diagnostic purposes.
@@ -1609,6 +1614,9 @@ void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
          (UnpackedFieldOffset & (UnpackedFieldAlign-1)) + FieldSize > TypeSize))
       UnpackedFieldOffset = llvm::RoundUpToAlignment(UnpackedFieldOffset,
                                                      UnpackedFieldAlign);
+    else if (ExplicitFieldAlign)
+      UnpackedFieldOffset = llvm::RoundUpToAlignment(UnpackedFieldOffset,
+                                                     ExplicitFieldAlign);
   }
 
   // If we're using external layout, give the external layout a chance