re PR target/52080 (Stores to bitfields introduce a store-data-race on adjacent data)

2012-03-14  Richard Guenther  <rguenther@suse.de>

	* tree.h (DECL_BIT_FIELD_REPRESENTATIVE): New define.
	* stor-layout.c (start_bitfield_representative): New function.
	(finish_bitfield_representative): Likewise.
	(finish_bitfield_layout): Likewise.
	(finish_record_layout): Call finish_bitfield_layout.
	* tree.c (free_lang_data_in_decl): Only free DECL_QUALIFIER
	for QUAL_UNION_TYPE fields.
	* tree-streamer-in.c (lto_input_ts_field_decl_tree_pointers):
	Stream DECL_BIT_FIELD_REPRESENTATIVE.
	* tree-streamer-out.c (write_ts_field_decl_tree_pointers): Likewise.

	PR middle-end/52080
	PR middle-end/52097
	PR middle-end/48124
	* expr.c (get_bit_range): Unconditionally extract bitrange
	from DECL_BIT_FIELD_REPRESENTATIVE.
	(expand_assignment): Adjust call to get_bit_range.

	* gcc.dg/torture/pr48124-1.c: New testcase.
	* gcc.dg/torture/pr48124-2.c: Likewise.
	* gcc.dg/torture/pr48124-3.c: Likewise.
	* gcc.dg/torture/pr48124-4.c: Likewise.

From-SVN: r185379

12 files changed, 370 insertions, 98 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4a3d0d1..04e1a00 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,25 @@
 2012-03-14  Richard Guenther  <rguenther@suse.de>
 
+	* tree.h (DECL_BIT_FIELD_REPRESENTATIVE): New define.
+	* stor-layout.c (start_bitfield_representative): New function.
+	(finish_bitfield_representative): Likewise.
+	(finish_bitfield_layout): Likewise.
+	(finish_record_layout): Call finish_bitfield_layout.
+	* tree.c (free_lang_data_in_decl): Only free DECL_QUALIFIER
+	for QUAL_UNION_TYPE fields.
+	* tree-streamer-in.c (lto_input_ts_field_decl_tree_pointers):
+	Stream DECL_BIT_FIELD_REPRESENTATIVE.
+	* tree-streamer-out.c (write_ts_field_decl_tree_pointers): Likewise.
+
+	PR middle-end/52080
+	PR middle-end/52097
+	PR middle-end/48124
+	* expr.c (get_bit_range): Unconditionally extract bitrange
+	from DECL_BIT_FIELD_REPRESENTATIVE.
+	(expand_assignment): Adjust call to get_bit_range.
+
+2012-03-14  Richard Guenther  <rguenther@suse.de>
+
 	PR middle-end/52578
 	* fold-const.c (fold_unary_loc): Fold (T1)(T2)x to (T1)x if
 	the outermost conversion is a sign-change only.
diff --git a/gcc/expr.c b/gcc/expr.c
index 59b76a4..e8dce74 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4439,113 +4439,43 @@ optimize_bitfield_assignment_op (unsigned HOST_WIDE_INT bitsize,
 /* In the C++ memory model, consecutive bit fields in a structure are
    considered one memory location.
 
-   Given a COMPONENT_REF, this function returns the bit range of
-   consecutive bits in which this COMPONENT_REF belongs in.  The
-   values are returned in *BITSTART and *BITEND.  If either the C++
-   memory model is not activated, or this memory access is not thread
-   visible, 0 is returned in *BITSTART and *BITEND.
-
-   EXP is the COMPONENT_REF.
-   INNERDECL is the actual object being referenced.
-   BITPOS is the position in bits where the bit starts within the structure.
-   BITSIZE is size in bits of the field being referenced in EXP.
-
-   For example, while storing into FOO.A here...
-
-      struct {
-        BIT 0:
-          unsigned int a : 4;
-	  unsigned int b : 1;
-	BIT 8:
-	  unsigned char c;
-	  unsigned int d : 6;
-      } foo;
-
-   ...we are not allowed to store past <b>, so for the layout above, a
-   range of 0..7 (because no one cares if we store into the
-   padding).  */
+   Given a COMPONENT_REF EXP at bit position BITPOS, this function
+   returns the bit range of consecutive bits in which this COMPONENT_REF
+   belongs in.  The values are returned in *BITSTART and *BITEND.
+   If the access does not need to be restricted 0 is returned in
+   *BITSTART and *BITEND.  */
 
 static void
 get_bit_range (unsigned HOST_WIDE_INT *bitstart,
 	       unsigned HOST_WIDE_INT *bitend,
-	       tree exp, tree innerdecl,
-	       HOST_WIDE_INT bitpos, HOST_WIDE_INT bitsize)
+	       tree exp,
+	       HOST_WIDE_INT bitpos)
 {
-  tree field, record_type, fld;
-  bool found_field = false;
-  bool prev_field_is_bitfield;
+  unsigned HOST_WIDE_INT bitoffset;
+  tree field, repr, offset;
 
   gcc_assert (TREE_CODE (exp) == COMPONENT_REF);
 
-  /* If other threads can't see this value, no need to restrict stores.  */
-  if (ALLOW_STORE_DATA_RACES
-      || ((TREE_CODE (innerdecl) == MEM_REF
-	   || TREE_CODE (innerdecl) == TARGET_MEM_REF)
-	  && !ptr_deref_may_alias_global_p (TREE_OPERAND (innerdecl, 0)))
-      || (DECL_P (innerdecl)
-	  && ((TREE_CODE (innerdecl) == VAR_DECL
-	       && DECL_THREAD_LOCAL_P (innerdecl))
-	      || !TREE_STATIC (innerdecl))))
+  field = TREE_OPERAND (exp, 1);
+  repr = DECL_BIT_FIELD_REPRESENTATIVE (field);
+  /* If we do not have a DECL_BIT_FIELD_REPRESENTATIVE there is no
+     need to limit the range we can access.  */
+  if (!repr)
     {
       *bitstart = *bitend = 0;
       return;
     }
 
-  /* Bit field we're storing into.  */
-  field = TREE_OPERAND (exp, 1);
-  record_type = DECL_FIELD_CONTEXT (field);
-
-  /* Count the contiguous bitfields for the memory location that
-     contains FIELD.  */
-  *bitstart = 0;
-  prev_field_is_bitfield = true;
-  for (fld = TYPE_FIELDS (record_type); fld; fld = DECL_CHAIN (fld))
-    {
-      tree t, offset;
-      enum machine_mode mode;
-      int unsignedp, volatilep;
-
-      if (TREE_CODE (fld) != FIELD_DECL)
-	continue;
-
-      t = build3 (COMPONENT_REF, TREE_TYPE (exp),
-		  unshare_expr (TREE_OPERAND (exp, 0)),
-		  fld, NULL_TREE);
-      get_inner_reference (t, &bitsize, &bitpos, &offset,
-			   &mode, &unsignedp, &volatilep, true);
-
-      if (field == fld)
-	found_field = true;
-
-      if (DECL_BIT_FIELD_TYPE (fld) && bitsize > 0)
-	{
-	  if (prev_field_is_bitfield == false)
-	    {
-	      *bitstart = bitpos;
-	      prev_field_is_bitfield = true;
-	    }
-	}
-      else
-	{
-	  prev_field_is_bitfield = false;
-	  if (found_field)
-	    break;
-	}
-    }
-  gcc_assert (found_field);
+  /* Compute the adjustment to bitpos from the offset of the field
+     relative to the representative.  */
+  offset = size_diffop (DECL_FIELD_OFFSET (field),
+			DECL_FIELD_OFFSET (repr));
+  bitoffset = (tree_low_cst (offset, 1) * BITS_PER_UNIT
+	       + tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1)
+	       - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
 
-  if (fld)
-    {
-      /* We found the end of the bit field sequence.  Include the
-	 padding up to the next field and be done.  */
-      *bitend = bitpos - 1;
-    }
-  else
-    {
-      /* If this is the last element in the structure, include the padding
-	 at the end of structure.  */
-      *bitend = TREE_INT_CST_LOW (TYPE_SIZE (record_type)) - 1;
-    }
+  *bitstart = bitpos - bitoffset;
+  *bitend = *bitstart + tree_low_cst (DECL_SIZE (repr), 1) - 1;
 }
 
 /* Returns true if the MEM_REF REF refers to an object that does not
@@ -4682,8 +4612,7 @@ expand_assignment (tree to, tree from, bool nontemporal)
 
       if (TREE_CODE (to) == COMPONENT_REF
 	  && DECL_BIT_FIELD_TYPE (TREE_OPERAND (to, 1)))
-	get_bit_range (&bitregion_start, &bitregion_end,
-		       to, tem, bitpos, bitsize);
+	get_bit_range (&bitregion_start, &bitregion_end, to, bitpos);
 
       /* If we are going to use store_bit_field and extract_bit_field,
 	 make sure to_rtx will be safe for multiple use.  */
diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
index a1ac000..7c7fabc 100644
--- a/gcc/stor-layout.c
+++ b/gcc/stor-layout.c
@@ -1722,6 +1722,190 @@ finalize_type_size (tree type)
     }
 }
 
+/* Return a new underlying object for a bitfield started with FIELD.  */
+
+static tree
+start_bitfield_representative (tree field)
+{
+  tree repr = make_node (FIELD_DECL);
+  DECL_FIELD_OFFSET (repr) = DECL_FIELD_OFFSET (field);
+  /* Force the representative to begin at a BITS_PER_UNIT aligned
+     boundary - C++ may use tail-padding of a base object to
+     continue packing bits so the bitfield region does not start
+     at bit zero (see g++.dg/abi/bitfield5.C for example).
+     Unallocated bits may happen for other reasons as well,
+     for example Ada which allows explicit bit-granular structure layout.  */
+  DECL_FIELD_BIT_OFFSET (repr)
+    = size_binop (BIT_AND_EXPR,
+		  DECL_FIELD_BIT_OFFSET (field),
+		  bitsize_int (~(BITS_PER_UNIT - 1)));
+  SET_DECL_OFFSET_ALIGN (repr, DECL_OFFSET_ALIGN (field));
+  DECL_SIZE (repr) = DECL_SIZE (field);
+  DECL_SIZE_UNIT (repr) = DECL_SIZE_UNIT (field);
+  DECL_PACKED (repr) = DECL_PACKED (field);
+  DECL_CONTEXT (repr) = DECL_CONTEXT (field);
+  return repr;
+}
+
+/* Finish up a bitfield group that was started by creating the underlying
+   object REPR with the last field in the bitfield group FIELD.  */
+
+static void
+finish_bitfield_representative (tree repr, tree field)
+{
+  unsigned HOST_WIDE_INT bitsize, maxbitsize;
+  enum machine_mode mode;
+  tree nextf, size;
+
+  size = size_diffop (DECL_FIELD_OFFSET (field),
+		      DECL_FIELD_OFFSET (repr));
+  gcc_assert (host_integerp (size, 1));
+  bitsize = (tree_low_cst (size, 1) * BITS_PER_UNIT
+	     + tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1)
+	     - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1)
+	     + tree_low_cst (DECL_SIZE (field), 1));
+
+  /* Now nothing tells us how to pad out bitsize ...  */
+  nextf = DECL_CHAIN (field);
+  while (nextf && TREE_CODE (nextf) != FIELD_DECL)
+    nextf = DECL_CHAIN (nextf);
+  if (nextf)
+    {
+      tree maxsize;
+      /* If there was an error, the field may be not layed out
+         correctly.  Don't bother to do anything.  */
+      if (TREE_TYPE (nextf) == error_mark_node)
+	return;
+      maxsize = size_diffop (DECL_FIELD_OFFSET (nextf),
+			     DECL_FIELD_OFFSET (repr));
+      gcc_assert (host_integerp (maxsize, 1));
+      maxbitsize = (tree_low_cst (maxsize, 1) * BITS_PER_UNIT
+		    + tree_low_cst (DECL_FIELD_BIT_OFFSET (nextf), 1)
+		    - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
+    }
+  else
+    {
+      /* ???  If you consider that tail-padding of this struct might be
+         re-used when deriving from it we cannot really do the following
+	 and thus need to set maxsize to bitsize?  */
+      tree maxsize = size_diffop (TYPE_SIZE_UNIT (DECL_CONTEXT (field)),
+				  DECL_FIELD_OFFSET (repr));
+      gcc_assert (host_integerp (maxsize, 1));
+      maxbitsize = (tree_low_cst (maxsize, 1) * BITS_PER_UNIT
+		    - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
+    }
+
+  /* Only if we don't artificially break up the representative in
+     the middle of a large bitfield with different possibly
+     overlapping representatives.  And all representatives start
+     at byte offset.  */
+  gcc_assert (maxbitsize % BITS_PER_UNIT == 0);
+
+  /* Round up bitsize to multiples of BITS_PER_UNIT.  */
+  bitsize = (bitsize + BITS_PER_UNIT - 1) & ~(BITS_PER_UNIT - 1);
+
+  /* Find the smallest nice mode to use.  */
+  for (mode = GET_CLASS_NARROWEST_MODE (MODE_INT); mode != VOIDmode;
+       mode = GET_MODE_WIDER_MODE (mode))
+    if (GET_MODE_BITSIZE (mode) >= bitsize)
+      break;
+  if (mode != VOIDmode
+      && (GET_MODE_BITSIZE (mode) > maxbitsize
+	  || GET_MODE_BITSIZE (mode) > MAX_FIXED_MODE_SIZE))
+    mode = VOIDmode;
+
+  if (mode == VOIDmode)
+    {
+      /* We really want a BLKmode representative only as a last resort,
+         considering the member b in
+	   struct { int a : 7; int b : 17; int c; } __attribute__((packed));
+	 Otherwise we simply want to split the representative up
+	 allowing for overlaps within the bitfield region as required for
+	   struct { int a : 7; int b : 7;
+		    int c : 10; int d; } __attribute__((packed));
+	 [0, 15] HImode for a and b, [8, 23] HImode for c.  */
+      DECL_SIZE (repr) = bitsize_int (bitsize);
+      DECL_SIZE_UNIT (repr) = size_int (bitsize / BITS_PER_UNIT);
+      DECL_MODE (repr) = BLKmode;
+      TREE_TYPE (repr) = build_array_type_nelts (unsigned_char_type_node,
+						 bitsize / BITS_PER_UNIT);
+    }
+  else
+    {
+      unsigned HOST_WIDE_INT modesize = GET_MODE_BITSIZE (mode);
+      DECL_SIZE (repr) = bitsize_int (modesize);
+      DECL_SIZE_UNIT (repr) = size_int (modesize / BITS_PER_UNIT);
+      DECL_MODE (repr) = mode;
+      TREE_TYPE (repr) = lang_hooks.types.type_for_mode (mode, 1);
+    }
+
+  /* Remember whether the bitfield group is at the end of the
+     structure or not.  */
+  DECL_CHAIN (repr) = nextf;
+}
+
+/* Compute and set FIELD_DECLs for the underlying objects we should
+   use for bitfield access for the structure layed out with RLI.  */
+
+static void
+finish_bitfield_layout (record_layout_info rli)
+{
+  tree field, prev;
+  tree repr = NULL_TREE;
+
+  /* Unions would be special, for the ease of type-punning optimizations
+     we could use the underlying type as hint for the representative
+     if the bitfield would fit and the representative would not exceed
+     the union in size.  */
+  if (TREE_CODE (rli->t) != RECORD_TYPE)
+    return;
+
+  for (prev = NULL_TREE, field = TYPE_FIELDS (rli->t);
+       field; field = DECL_CHAIN (field))
+    {
+      if (TREE_CODE (field) != FIELD_DECL)
+	continue;
+
+      /* In the C++ memory model, consecutive bit fields in a structure are
+	 considered one memory location and updating a memory location
+	 may not store into adjacent memory locations.  */
+      if (!repr
+	  && DECL_BIT_FIELD_TYPE (field))
+	{
+	  /* Start new representative.  */
+	  repr = start_bitfield_representative (field);
+	}
+      else if (repr
+	       && ! DECL_BIT_FIELD_TYPE (field))
+	{
+	  /* Finish off new representative.  */
+	  finish_bitfield_representative (repr, prev);
+	  repr = NULL_TREE;
+	}
+      else if (DECL_BIT_FIELD_TYPE (field))
+	{
+	  /* Zero-size bitfields finish off a representative and
+	     do not have a representative themselves.  This is
+	     required by the C++ memory model.  */
+	  if (integer_zerop (DECL_SIZE (field)))
+	    {
+	      finish_bitfield_representative (repr, prev);
+	      repr = NULL_TREE;
+	    }
+	}
+      else
+	continue;
+
+      if (repr)
+	DECL_BIT_FIELD_REPRESENTATIVE (field) = repr;
+
+      prev = field;
+    }
+
+  if (repr)
+    finish_bitfield_representative (repr, prev);
+}
+
 /* Do all of the work required to layout the type indicated by RLI,
    once the fields have been laid out.  This function will call `free'
    for RLI, unless FREE_P is false.  Passing a value other than false
@@ -1742,6 +1926,9 @@ finish_record_layout (record_layout_info rli, int free_p)
   /* Perform any last tweaks to the TYPE_SIZE, etc.  */
   finalize_type_size (rli->t);
 
+  /* Compute bitfield representatives.  */
+  finish_bitfield_layout (rli);
+
   /* Propagate TYPE_PACKED to variants.  With C++ templates,
      handle_packed_attribute is too early to do this.  */
   for (variant = TYPE_NEXT_VARIANT (rli->t); variant;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index b4626f3..406f095 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,15 @@
 2012-03-14  Richard Guenther  <rguenther@suse.de>
 
+	PR middle-end/52080
+	PR middle-end/52097
+	PR middle-end/48124
+	* gcc.dg/torture/pr48124-1.c: New testcase.
+	* gcc.dg/torture/pr48124-2.c: Likewise.
+	* gcc.dg/torture/pr48124-3.c: Likewise.
+	* gcc.dg/torture/pr48124-4.c: Likewise.
+
+2012-03-14  Richard Guenther  <rguenther@suse.de>
+
 	PR middle-end/52578
 	* gcc.dg/pr52578.c: New testcase.
 
diff --git a/gcc/testsuite/gcc.dg/torture/pr48124-1.c b/gcc/testsuite/gcc.dg/torture/pr48124-1.c
new file mode 100644
index 0000000..ed76181
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr48124-1.c
@@ -0,0 +1,33 @@
+/* { dg-do run } */
+/* { dg-options "-fno-toplevel-reorder" } */
+
+extern void abort (void);
+
+struct S
+{
+  signed a : 26;
+  signed b : 16;
+  signed c : 10;
+  volatile signed d : 14;
+};
+
+static struct S e = { 0, 0, 0, 1 };
+static int f = 1;
+
+void __attribute__((noinline))
+foo (void)
+{
+  e.d = 0;
+  f = 2;
+}
+
+int
+main ()
+{
+  if (e.a || e.b || e.c || e.d != 1 || f != 1)
+    abort ();
+  foo ();
+  if (e.a || e.b || e.c || e.d || f != 2)
+    abort ();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr48124-2.c b/gcc/testsuite/gcc.dg/torture/pr48124-2.c
new file mode 100644
index 0000000..485d8d4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr48124-2.c
@@ -0,0 +1,27 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+static volatile struct S0 {
+    short f3[9];
+    unsigned f8 : 15;
+} s = {1};
+static unsigned short sh = 0x1234;
+
+struct S0 a, b;
+int vi = 0;
+
+void func_4()
+{
+  s.f8 |= 1;
+  sh = 15;
+  if (vi) a = b;
+}
+
+int main()
+{
+  func_4();
+  if (sh != 15)
+    abort ();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr48124-3.c b/gcc/testsuite/gcc.dg/torture/pr48124-3.c
new file mode 100644
index 0000000..386d88b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr48124-3.c
@@ -0,0 +1,32 @@
+/* { dg-do run } */
+
+extern void abort (void);
+struct S1
+{
+  int f0;
+  int:1;
+  int f3;
+  int:1;
+  int:0;
+  int f6:1;
+};
+int g_13 = 1;
+volatile struct S1 g_118 = {
+    1
+};
+
+void __attribute__((noinline))
+func_46 ()
+{
+  for (g_13 = 0; g_13 >= 0; g_13 -= 1)
+    g_118.f6 = 0;
+}
+
+int
+main ()
+{
+  func_46 ();
+  if (g_13 != -1)
+    abort ();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr48124-4.c b/gcc/testsuite/gcc.dg/torture/pr48124-4.c
new file mode 100644
index 0000000..9ccd763
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr48124-4.c
@@ -0,0 +1,28 @@
+/* { dg-do run } */
+
+extern void abort (void);
+struct S1 {
+    unsigned f0, f1;
+    unsigned short f2, f3;
+    unsigned f4 : 16;
+    unsigned f5, f6;
+    volatile unsigned f7 : 28;
+};
+static struct S1 g_76;
+static struct S1 g_245 = {0,0,0,0,0,0,0,1};
+static signed char g_323 = 0x80;
+static void func_1(void)
+{
+  g_245.f7 &= 1;
+  for (g_323 = 0; g_323 <= -1; g_323 -= 2) {
+      g_76 = g_76;
+      g_76.f4 ^= 11;
+  }
+}
+int main()
+{
+  func_1();
+  if (g_323 != 0 || g_245.f7 != 1)
+    abort ();
+  return 0;
+}
diff --git a/gcc/tree-streamer-in.c b/gcc/tree-streamer-in.c
index cc6fae7..cb940aa 100644
--- a/gcc/tree-streamer-in.c
+++ b/gcc/tree-streamer-in.c
@@ -640,7 +640,7 @@ lto_input_ts_field_decl_tree_pointers (struct lto_input_block *ib,
 {
   DECL_FIELD_OFFSET (expr) = stream_read_tree (ib, data_in);
   DECL_BIT_FIELD_TYPE (expr) = stream_read_tree (ib, data_in);
-  /* Do not stream DECL_QUALIFIER, it is useless after gimplification.  */
+  DECL_BIT_FIELD_REPRESENTATIVE (expr) = stream_read_tree (ib, data_in);
   DECL_FIELD_BIT_OFFSET (expr) = stream_read_tree (ib, data_in);
   DECL_FCONTEXT (expr) = stream_read_tree (ib, data_in);
 }
diff --git a/gcc/tree-streamer-out.c b/gcc/tree-streamer-out.c
index 21689df..c792fc2 100644
--- a/gcc/tree-streamer-out.c
+++ b/gcc/tree-streamer-out.c
@@ -552,7 +552,7 @@ write_ts_field_decl_tree_pointers (struct output_block *ob, tree expr,
 {
   stream_write_tree (ob, DECL_FIELD_OFFSET (expr), ref_p);
   stream_write_tree (ob, DECL_BIT_FIELD_TYPE (expr), ref_p);
-  /* Do not stream DECL_QUALIFIER, it is useless after gimplification.  */
+  stream_write_tree (ob, DECL_BIT_FIELD_REPRESENTATIVE (expr), ref_p);
   stream_write_tree (ob, DECL_FIELD_BIT_OFFSET (expr), ref_p);
   stream_write_tree (ob, DECL_FCONTEXT (expr), ref_p);
 }
diff --git a/gcc/tree.c b/gcc/tree.c
index 3989a9b..c90331c 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -4633,7 +4633,8 @@ free_lang_data_in_decl (tree decl)
   if (TREE_CODE (decl) == FIELD_DECL)
     {
       free_lang_data_in_one_sizepos (&DECL_FIELD_OFFSET (decl));
-      DECL_QUALIFIER (decl) = NULL_TREE;
+      if (TREE_CODE (DECL_CONTEXT (decl)) == QUAL_UNION_TYPE)
+	DECL_QUALIFIER (decl) = NULL_TREE;
     }
 
  if (TREE_CODE (decl) == FUNCTION_DECL)
diff --git a/gcc/tree.h b/gcc/tree.h
index 0a2d619..d9e826b 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -3024,6 +3024,11 @@ struct GTY(()) tree_decl_with_rtl {
 #define DECL_BIT_FIELD_TYPE(NODE) \
   (FIELD_DECL_CHECK (NODE)->field_decl.bit_field_type)
 
+/* In a FIELD_DECL of a RECORD_TYPE, this is a pointer to the storage
+   representative FIELD_DECL.  */
+#define DECL_BIT_FIELD_REPRESENTATIVE(NODE) \
+  (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
+
 /* For a FIELD_DECL in a QUAL_UNION_TYPE, records the expression, which
    if nonzero, indicates that the field occupies the type.  */
 #define DECL_QUALIFIER(NODE) (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)