[llvm-branch-commits] [cfe-branch] r113272 - /cfe/branches/Apple/williamson/lib/CodeGen/CGObjCMac.cpp

[Daniel Dunbar]

Author: ddunbar
Date: Tue Sep  7 15:35:20 2010
New Revision: 113272

URL: http://llvm.org/viewvc/llvm-project?rev=113272&view=rev
Log:
Merge r112914:
--
Author: Daniel Dunbar <daniel at zuster.org>
Date:   Thu Sep 2 23:53:31 2010 +0000

    IRgen/Obj-C: Rewrite Objective-C bit-field access to compute the access strategy
    using the same methods as used for normal structures.
     - This fixes problems with reading past the end of the structure and with
       handling straddled bit-field access.

Modified:
    cfe/branches/Apple/williamson/lib/CodeGen/CGObjCMac.cpp

Modified: cfe/branches/Apple/williamson/lib/CodeGen/CGObjCMac.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/branches/Apple/williamson/lib/CodeGen/CGObjCMac.cpp?rev=113272&r1=113271&r2=113272&view=diff
==============================================================================
--- cfe/branches/Apple/williamson/lib/CodeGen/CGObjCMac.cpp (original)
+++ cfe/branches/Apple/williamson/lib/CodeGen/CGObjCMac.cpp Tue Sep  7 15:35:20 2010
@@ -113,11 +113,27 @@
   if (!Ivar->isBitField())
     return LValue::MakeAddr(V, Quals);
 
-  // We need to compute the bit offset for the bit-field, the offset is to the
-  // byte. Note, there is a subtle invariant here: we can only call this routine
-  // on non-synthesized ivars but we may be called for synthesized ivars.
-  // However, a synthesized ivar can never be a bit-field, so this is safe.
-  uint64_t BitOffset = LookupFieldBitOffset(CGF.CGM, OID, 0, Ivar) % 8;
+  // We need to compute an access strategy for this bit-field. We are given the
+  // offset to the first byte in the bit-field, the sub-byte offset is taken
+  // from the original layout. We reuse the normal bit-field access strategy by
+  // treating this as an access to a struct where the bit-field is in byte 0,
+  // and adjust the containing type size as appropriate.
+  //
+  // FIXME: Note that currently we make a very conservative estimate of the
+  // alignment of the bit-field, because (a) it is not clear what guarantees the
+  // runtime makes us, and (b) we don't have a way to specify that the struct is
+  // at an alignment plus offset.
+  //
+  // Note, there is a subtle invariant here: we can only call this routine on
+  // non-synthesized ivars but we may be called for synthesized ivars.  However,
+  // a synthesized ivar can never be a bit-field, so this is safe.
+  const ASTRecordLayout &RL =
+    CGF.CGM.getContext().getASTObjCInterfaceLayout(OID);
+  uint64_t TypeSizeInBits = RL.getSize();
+  uint64_t FieldBitOffset = LookupFieldBitOffset(CGF.CGM, OID, 0, Ivar);
+  uint64_t BitOffset = FieldBitOffset % 8;
+  uint64_t ContainingTypeAlign = 8;
+  uint64_t ContainingTypeSize = TypeSizeInBits - (FieldBitOffset - BitOffset);
   uint64_t BitFieldSize =
     Ivar->getBitWidth()->EvaluateAsInt(CGF.getContext()).getZExtValue();
 
@@ -127,20 +143,9 @@
   // layout object. However, this is blocked on other cleanups to the
   // Objective-C code, so for now we just live with allocating a bunch of these
   // objects.
-
-  // We always construct a single, possibly unaligned, access for this case.
-  CGBitFieldInfo::AccessInfo AI;
-  AI.FieldIndex = 0;
-  AI.FieldByteOffset = 0;
-  AI.FieldBitStart = BitOffset;
-  AI.AccessWidth = CGF.CGM.getContext().getTypeSize(IvarTy);
-  AI.AccessAlignment = 0;
-  AI.TargetBitOffset = 0;
-  AI.TargetBitWidth = BitFieldSize;
-
-  CGBitFieldInfo *Info =
-    new (CGF.CGM.getContext()) CGBitFieldInfo(BitFieldSize, 1, &AI,
-                                              IvarTy->isSignedIntegerType());
+  CGBitFieldInfo *Info = new (CGF.CGM.getContext()) CGBitFieldInfo(
+    CGBitFieldInfo::MakeInfo(CGF.CGM.getTypes(), Ivar, BitOffset, BitFieldSize,
+                             ContainingTypeSize, ContainingTypeAlign));
 
   // FIXME: We need to set a very conservative alignment on this, or make sure
   // that the runtime is doing the right thing.