Add TargetInfo::useBitfieldTypeAlignment().

 - Used to determine whether the alignment of the type in a bit-field is
   respected when laying out structures. The default is true, targets can
   override this as needed.

 - This is designed to correspond to the PCC_BITFIELD_TYPE_MATTERS macro in
   gcc. The AST/Sema implementation only affects one line, unless I have
   forgotten something. I'd appreciate further review.

 - IRgen still needs to be updated to fully support this (which is effectively
   PR5591).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@101356 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 6 insertions, 7 deletions

diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp
index bb73e7ea11..d312ee13fe 100644
--- a/lib/AST/RecordLayoutBuilder.cpp
+++ b/lib/AST/RecordLayoutBuilder.cpp
@@ -585,7 +585,7 @@ void ASTRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   uint64_t TypeSize = FieldInfo.first;
   unsigned FieldAlign = FieldInfo.second;
 
-  if (FieldPacked)
+  if (FieldPacked || !Ctx.Target.useBitfieldTypeAlignment())
     FieldAlign = 1;
   if (const AlignedAttr *AA = D->getAttr<AlignedAttr>())
     FieldAlign = std::max(FieldAlign, AA->getMaxAlignment());
@@ -594,12 +594,11 @@ void ASTRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   if (MaxFieldAlignment)
     FieldAlign = std::min(FieldAlign, MaxFieldAlignment);
 
-  // Check if we need to add padding to give the field the correct
-  // alignment.
+  // Check if we need to add padding to give the field the correct alignment.
   if (FieldSize == 0 || (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)
     FieldOffset = (FieldOffset + (FieldAlign-1)) & ~(FieldAlign-1);
 
-  // Padding members don't affect overall alignment
+  // Padding members don't affect overall alignment.
   if (!D->getIdentifier())
     FieldAlign = 1;
 
diff --git a/lib/Basic/TargetInfo.cpp b/lib/Basic/TargetInfo.cpp
index 136089fe90..8b4fdee47c 100644
--- a/lib/Basic/TargetInfo.cpp
+++ b/lib/Basic/TargetInfo.cpp
@@ -20,9 +20,8 @@ using namespace clang;
 
 // TargetInfo Constructor.
 TargetInfo::TargetInfo(const std::string &T) : Triple(T) {
-  // Set defaults.  Defaults are set for a 32-bit RISC platform,
-  // like PPC or SPARC.
-  // These should be overridden by concrete targets as needed.
+  // Set defaults.  Defaults are set for a 32-bit RISC platform, like PPC or
+  // SPARC.  These should be overridden by concrete targets as needed.
   TLSSupported = true;
   PointerWidth = PointerAlign = 32;
   IntWidth = IntAlign = 32;
@@ -45,6 +44,7 @@ TargetInfo::TargetInfo(const std::string &T) : Triple(T) {
   Char32Type = UnsignedInt;
   Int64Type = SignedLongLong;
   SigAtomicType = SignedInt;
+  UseBitfieldTypeAlignment = true;
   FloatFormat = &llvm::APFloat::IEEEsingle;
   DoubleFormat = &llvm::APFloat::IEEEdouble;
   LongDoubleFormat = &llvm::APFloat::IEEEdouble;