CodeGen: FieldMemcpyizer didn't handle copies starting inside bitfields
It's possible to construct cases where the first field we are trying to
copy is in the middle of an IR field. In some complicated cases, we
would fail to use an appropriate offset inside the object. Earlier
builds of clang seemed to miscompile the code by copying an insufficient
number of bytes. Up until now, we would assert: the copying offset was
insufficiently aligned.
This fixes PR21232.
llvm-svn: 219524
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 941e998..4976085 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -796,13 +796,13 @@
addNextField(F);
}
- CharUnits getMemcpySize() const {
+ CharUnits getMemcpySize(uint64_t FirstByteOffset) const {
unsigned LastFieldSize =
LastField->isBitField() ?
LastField->getBitWidthValue(CGF.getContext()) :
CGF.getContext().getTypeSize(LastField->getType());
uint64_t MemcpySizeBits =
- LastFieldOffset + LastFieldSize - FirstFieldOffset +
+ LastFieldOffset + LastFieldSize - FirstByteOffset +
CGF.getContext().getCharWidth() - 1;
CharUnits MemcpySize =
CGF.getContext().toCharUnitsFromBits(MemcpySizeBits);
@@ -818,19 +818,31 @@
CharUnits Alignment;
+ uint64_t FirstByteOffset;
if (FirstField->isBitField()) {
const CGRecordLayout &RL =
CGF.getTypes().getCGRecordLayout(FirstField->getParent());
const CGBitFieldInfo &BFInfo = RL.getBitFieldInfo(FirstField);
Alignment = CharUnits::fromQuantity(BFInfo.StorageAlignment);
+ // FirstFieldOffset is not appropriate for bitfields,
+ // it won't tell us what the storage offset should be and thus might not
+ // be properly aligned.
+ //
+ // Instead calculate the storage offset using the offset of the field in
+ // the struct type.
+ const llvm::DataLayout &DL = CGF.CGM.getDataLayout();
+ FirstByteOffset =
+ DL.getStructLayout(RL.getLLVMType())
+ ->getElementOffsetInBits(RL.getLLVMFieldNo(FirstField));
} else {
Alignment = CGF.getContext().getDeclAlign(FirstField);
+ FirstByteOffset = FirstFieldOffset;
}
- assert((CGF.getContext().toCharUnitsFromBits(FirstFieldOffset) %
+ assert((CGF.getContext().toCharUnitsFromBits(FirstByteOffset) %
Alignment) == 0 && "Bad field alignment.");
- CharUnits MemcpySize = getMemcpySize();
+ CharUnits MemcpySize = getMemcpySize(FirstByteOffset);
QualType RecordTy = CGF.getContext().getTypeDeclType(ClassDecl);
llvm::Value *ThisPtr = CGF.LoadCXXThis();
LValue DestLV = CGF.MakeNaturalAlignAddrLValue(ThisPtr, RecordTy);