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
diff --git a/include/clang/Basic/TargetInfo.h b/include/clang/Basic/TargetInfo.h
index bc2cf19..55669fa 100644
--- a/include/clang/Basic/TargetInfo.h
+++ b/include/clang/Basic/TargetInfo.h
@@ -85,6 +85,14 @@
protected:
IntType SizeType, IntMaxType, UIntMaxType, PtrDiffType, IntPtrType, WCharType,
WIntType, Char16Type, Char32Type, Int64Type, SigAtomicType;
+
+ /// Control whether the alignment of bit-field types is respected when laying
+ /// out structures. If true, then the alignment of the bit-field type will be
+ /// used to (a) impact the alignment of the containing structure, and (b)
+ /// ensure that the individual bit-field will not straddle an alignment
+ /// boundary.
+ unsigned UseBitfieldTypeAlignment : 1;
+
public:
IntType getSizeType() const { return SizeType; }
IntType getIntMaxType() const { return IntMaxType; }
@@ -197,6 +205,10 @@
return UserLabelPrefix;
}
+ bool useBitfieldTypeAlignment() const {
+ return UseBitfieldTypeAlignment;
+ }
+
/// getTypeName - Return the user string for the specified integer type enum.
/// For example, SignedShort -> "short".
static const char *getTypeName(IntType T);
diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp
index bb73e7e..d312ee1 100644
--- a/lib/AST/RecordLayoutBuilder.cpp
+++ b/lib/AST/RecordLayoutBuilder.cpp
@@ -585,7 +585,7 @@
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 @@
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 136089f..8b4fdee 100644
--- a/lib/Basic/TargetInfo.cpp
+++ b/lib/Basic/TargetInfo.cpp
@@ -20,9 +20,8 @@
// 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 @@
Char32Type = UnsignedInt;
Int64Type = SignedLongLong;
SigAtomicType = SignedInt;
+ UseBitfieldTypeAlignment = true;
FloatFormat = &llvm::APFloat::IEEEsingle;
DoubleFormat = &llvm::APFloat::IEEEdouble;
LongDoubleFormat = &llvm::APFloat::IEEEdouble;