================
Comment at: lib/CodeGen/CGAtomic.cpp:77
@@ +76,3 @@
+ auto &OrigBFI = lvalue.getBitFieldInfo();
+ auto OffsetInChars = C.toCharUnitsFromBits(OrigBFI.Offset);
+ auto VoidPtrAddr = CGF.EmitCastToVoidPtr(lvalue.getBitFieldAddr());
----------------
Hmm. I feel like you should make sure that your rule uses an aligned atomic
access if it's possible to do so. That is, if the bitfield does fall within a
single aligned unit, you should definitely access it with an atomic of that
size. I think you need to consider the actual bitfield width for this, but
maybe I'm missing something and that's done implicitly elsewhere.
================
Comment at: lib/CodeGen/CGAtomic.cpp:86
@@ +85,3 @@
+ BFI.Offset %= C.getCharWidth();
+ BFI.StorageSize = AtomicSizeInBits;
+ LVal = LValue::MakeBitfield(Addr, BFI, lvalue.getType(),
----------------
This is dangerous; I think you can end up with an access that goes beyond the
end of the structure with this. Consider a 1-bit bitfield of type "unsigned"
that's at the end of the struct, e.g.
struct {
unsigned : 31
unsigned x : 1; // <- access is to this
};
You need to make sure this is only accessed with an 8-bit operation.
================
Comment at: lib/CodeGen/CGAtomic.cpp:88
@@ +87,3 @@
+ LVal = LValue::MakeBitfield(Addr, BFI, lvalue.getType(),
+ lvalue.getAlignment());
+ } else if (lvalue.isVectorElt()) {
----------------
This alignment needs to be adjusted.
http://reviews.llvm.org/D6431
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