From: Mark Mitchell <mark@codesourcery.com>
Date: Sun, 23 Apr 2006 18:04:33 +0000 (+0000)
Subject: re PR c++/26534 ([4.1] bitfield wrong optimize)
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=38a4afeecdf392267ff73a27a69f458b5d8b424c;p=gcc.git

re PR c++/26534 ([4.1] bitfield wrong optimize)

2006-04-23  Mark Mitchell  <mark@codesourcery.com>

	PR c++/26534
	* c-common.h (c_build_bitfield_integer_type): Declare.
	* c-decl.c (c_build_bitfield_integer_type): Move to ...
	* c-common.c (c_build_bitfield_integer_type): ... here.

2006-04-23  Mark Mitchell  <mark@codesourcery.com>

	PR c++/26534
	* cp-tree.h (is_bitfield_expr_with_lowered_type): New function.
	* typeck.c (is_bitfield_expr_with_lowered_type): New function.
	(decay_conversion): Convert bitfield expressions to the correct
	type.
	(build_modify_expr): Remove spurious conversions.
	* class.c (layout_class_type): Modify the type of bitfields to
	indicate a limited range.
	* call.c (standard_conversion): Adjust the type of bitfield
	expressions used in an rvalue context.
	(build_conditional_expr): Likewise.

2006-04-23  Mark Mitchell  <mark@codesourcery.com>

	PR c++/26534
	* g++.dg/opt/bitfield1.C: New test.
	* g++.dg/compat/abi/bitfield1_main.C: Add -w.
	* g++.dg/compat/abi/bitfield1_x.C: Likewise.
	* g++.dg/compat/abi/bitfield1_y.C: Likewise.
	* g++.dg/compat/abi/bitfield2_main.C: Likewise.
	* g++.dg/compat/abi/bitfield2_x.C: Likewise.
	* g++.dg/compat/abi/bitfield2_y.C: Likewise.
	* g++.dg/abi/bitfield1.C: Add dg-warning markers.
	* g++.dg/abi/bitfield2.C: Likewise.
	* g++.dg/init/bitfield1.C: Likewise.

From-SVN: r113199
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ea6d17b2b23..08fc7c0197e 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2006-04-23  Mark Mitchell  <mark@codesourcery.com>
+
+	PR c++/26534
+	* c-common.h (c_build_bitfield_integer_type): Declare.
+	* c-decl.c (c_build_bitfield_integer_type): Move to ...
+	* c-common.c (c_build_bitfield_integer_type): ... here.
+
 2006-04-23  Roger Sayle  <roger@eyesopen.com>
 
 	PR target/21283
diff --git a/gcc/c-common.c b/gcc/c-common.c
index 1a11c3b189a..35982e58c1e 100644
--- a/gcc/c-common.c
+++ b/gcc/c-common.c
@@ -1871,6 +1871,31 @@ c_common_signed_or_unsigned_type (int unsignedp, tree type)
     return build_nonstandard_integer_type (TYPE_PRECISION (type), unsignedp);
 }
 
+/* Build a bit-field integer type for the given WIDTH and UNSIGNEDP.  */
+
+tree
+c_build_bitfield_integer_type (unsigned HOST_WIDE_INT width, int unsignedp)
+{
+  /* Extended integer types of the same width as a standard type have
+     lesser rank, so those of the same width as int promote to int or
+     unsigned int and are valid for printf formats expecting int or
+     unsigned int.  To avoid such special cases, avoid creating
+     extended integer types for bit-fields if a standard integer type
+     is available.  */
+  if (width == TYPE_PRECISION (integer_type_node))
+    return unsignedp ? unsigned_type_node : integer_type_node;
+  if (width == TYPE_PRECISION (signed_char_type_node))
+    return unsignedp ? unsigned_char_type_node : signed_char_type_node;
+  if (width == TYPE_PRECISION (short_integer_type_node))
+    return unsignedp ? short_unsigned_type_node : short_integer_type_node;
+  if (width == TYPE_PRECISION (long_integer_type_node))
+    return unsignedp ? long_unsigned_type_node : long_integer_type_node;
+  if (width == TYPE_PRECISION (long_long_integer_type_node))
+    return (unsignedp ? long_long_unsigned_type_node
+	    : long_long_integer_type_node);
+  return build_nonstandard_integer_type (width, unsignedp);
+}
+
 /* The C version of the register_builtin_type langhook.  */
 
 void
diff --git a/gcc/c-common.h b/gcc/c-common.h
index ed93f97b3e9..5636685efed 100644
--- a/gcc/c-common.h
+++ b/gcc/c-common.h
@@ -644,6 +644,7 @@ extern tree c_common_type_for_size (unsigned int, int);
 extern tree c_common_unsigned_type (tree);
 extern tree c_common_signed_type (tree);
 extern tree c_common_signed_or_unsigned_type (int, tree);
+extern tree c_build_bitfield_integer_type (unsigned HOST_WIDE_INT, int);
 extern tree c_common_truthvalue_conversion (tree);
 extern void c_apply_type_quals_to_decl (int, tree);
 extern tree c_sizeof_or_alignof_type (tree, bool, int);
diff --git a/gcc/c-decl.c b/gcc/c-decl.c
index db906b4456b..f4d33307bf2 100644
--- a/gcc/c-decl.c
+++ b/gcc/c-decl.c
@@ -3814,29 +3814,6 @@ check_bitfield_type_and_width (tree *type, tree *width, const char *orig_name)
     }
 }
 
-/* Build a bit-field integer type for the given WIDTH and UNSIGNEDP.  */
-static tree
-c_build_bitfield_integer_type (unsigned HOST_WIDE_INT width, int unsignedp)
-{
-  /* Extended integer types of the same width as a standard type have
-     lesser rank, so those of the same width as int promote to int or
-     unsigned int and are valid for printf formats expecting int or
-     unsigned int.  To avoid such special cases, avoid creating
-     extended integer types for bit-fields if a standard integer type
-     is available.  */
-  if (width == TYPE_PRECISION (integer_type_node))
-    return unsignedp ? unsigned_type_node : integer_type_node;
-  if (width == TYPE_PRECISION (signed_char_type_node))
-    return unsignedp ? unsigned_char_type_node : signed_char_type_node;
-  if (width == TYPE_PRECISION (short_integer_type_node))
-    return unsignedp ? short_unsigned_type_node : short_integer_type_node;
-  if (width == TYPE_PRECISION (long_integer_type_node))
-    return unsignedp ? long_unsigned_type_node : long_integer_type_node;
-  if (width == TYPE_PRECISION (long_long_integer_type_node))
-    return (unsignedp ? long_long_unsigned_type_node
-	    : long_long_integer_type_node);
-  return build_nonstandard_integer_type (width, unsignedp);
-}
 
 /* Given declspecs and a declarator,
    determine the name and type of the object declared
diff --git a/gcc/configure b/gcc/configure
index fe6f1bd3b4d..9137c4423e8 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -15843,6 +15843,10 @@ do
 	        lang_specs_files="$lang_specs_files $srcdir/$subdir/lang-specs.h"
 	    fi
 	    ;;
+        *)
+	    # This language is not enabled; skip it.
+	    continue
+	    ;;
         esac
 
 	if test -f $srcdir/$subdir/lang.opt; then
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 447f8270fb6..2fa8d99feb9 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -3325,6 +3325,10 @@ changequote(,)dnl
 	        lang_specs_files="$lang_specs_files $srcdir/$subdir/lang-specs.h"
 	    fi
 	    ;;
+        *)
+	    # This language is not enabled; skip it.
+	    continue
+	    ;;	
         esac
 changequote([,])dnl
 
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 711fb7c4072..a0a44a54075 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,17 @@
+2006-04-23  Mark Mitchell  <mark@codesourcery.com>
+
+	PR c++/26534
+	* cp-tree.h (is_bitfield_expr_with_lowered_type): New function.
+	* typeck.c (is_bitfield_expr_with_lowered_type): New function.
+	(decay_conversion): Convert bitfield expressions to the correct
+	type.
+	(build_modify_expr): Remove spurious conversions.
+	* class.c (layout_class_type): Modify the type of bitfields to
+	indicate a limited range. 
+	* call.c (standard_conversion): Adjust the type of bitfield
+	expressions used in an rvalue context.
+	(build_conditional_expr): Likewise.
+	
 2006-04-22  Kazu Hirata  <kazu@codesourcery.com>
 
 	* decl.c: Fix comment typos.
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index c9826451899..6743f924c2d 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -623,7 +623,16 @@ standard_conversion (tree to, tree from, tree expr, bool c_cast_p,
       conv = build_conv (ck_lvalue, from, conv);
     }
   else if (fromref || (expr && lvalue_p (expr)))
-    conv = build_conv (ck_rvalue, from, conv);
+    {
+      if (expr)
+	{
+	  tree bitfield_type;
+	  bitfield_type = is_bitfield_expr_with_lowered_type (expr);
+	  if (bitfield_type)
+	    from = bitfield_type;
+	}
+      conv = build_conv (ck_rvalue, from, conv);
+    }
 
    /* Allow conversion between `__complex__' data types.  */
   if (tcode == COMPLEX_TYPE && fcode == COMPLEX_TYPE)
@@ -3196,8 +3205,12 @@ build_conditional_expr (tree arg1, tree arg2, tree arg3)
      array-to-pointer (_conv.array_), and function-to-pointer
      (_conv.func_) standard conversions are performed on the second
      and third operands.  */
-  arg2_type = TREE_TYPE (arg2);
-  arg3_type = TREE_TYPE (arg3);
+  arg2_type = is_bitfield_expr_with_lowered_type (arg2);
+  if (!arg2_type)
+    arg2_type = TREE_TYPE (arg2);
+  arg3_type = is_bitfield_expr_with_lowered_type (arg3);
+  if (!arg3_type)
+    arg3_type = TREE_TYPE (arg3);
   if (VOID_TYPE_P (arg2_type) || VOID_TYPE_P (arg3_type))
     {
       /* Do the conversions.  We don't these for `void' type arguments
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index cc26cb8f56c..1cf87dc18a3 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -4727,6 +4727,29 @@ layout_class_type (tree t, tree *virtuals_p)
 		 "classes to be placed at different locations in a "
 		 "future version of GCC", field);
 
+      /* The middle end uses the type of expressions to determine the
+	 possible range of expression values.  In order to optimize
+	 "x.i > 7" to "false" for a 2-bit bitfield "i", the middle end
+	 must be made aware of the width of "i", via its type.  
+
+         Because C++ does not have integer types of arbitrary width,
+	 we must (for the purposes of the front end) convert from the
+	 type assigned here to the declared type of the bitfield
+	 whenever a bitfield expression is used as an rvalue.
+	 Similarly, when assigning a value to a bitfield, the value
+	 must be converted to the type given the bitfield here.  */
+      if (DECL_C_BIT_FIELD (field))
+	{
+	  tree ftype;
+	  unsigned HOST_WIDE_INT width;
+	  ftype = TREE_TYPE (field);
+	  width = tree_low_cst (DECL_SIZE (field), /*unsignedp=*/1);
+	  if (width != TYPE_PRECISION (ftype))
+	    TREE_TYPE (field) 
+	      = c_build_bitfield_integer_type (width, 
+					       TYPE_UNSIGNED (ftype));
+	}
+
       /* If we needed additional padding after this field, add it
 	 now.  */
       if (padding)
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 0848747687f..34cccc0a911 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -4351,6 +4351,7 @@ extern tree cxx_sizeof_or_alignof_expr		(tree, enum tree_code);
 extern tree cxx_sizeof_or_alignof_type		(tree, enum tree_code, bool);
 #define cxx_sizeof_nowarn(T) cxx_sizeof_or_alignof_type (T, SIZEOF_EXPR, false)
 extern tree inline_conversion			(tree);
+extern tree is_bitfield_expr_with_lowered_type  (tree); 
 extern tree decay_conversion			(tree);
 extern tree default_conversion			(tree);
 extern tree build_class_member_access_expr      (tree, tree, tree, bool);
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index a7bdd55dcc7..7fc6cab7aea 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -1398,21 +1398,47 @@ invalid_nonstatic_memfn_p (tree expr)
   return false;
 }
 
+/* If EXP is a reference to a bitfield, and the type of EXP does not
+   match the declared type of the bitfield, return the declared type
+   of the bitfield.  Otherwise, return NULL_TREE.  */
+
+tree
+is_bitfield_expr_with_lowered_type (tree exp)
+{
+  tree field;
+
+  if (TREE_CODE (exp) == COND_EXPR)
+    {
+      if (!is_bitfield_expr_with_lowered_type (TREE_OPERAND (exp, 1)))
+	return NULL_TREE;
+      return is_bitfield_expr_with_lowered_type (TREE_OPERAND (exp, 2));
+    }
+  if (TREE_CODE (exp) != COMPONENT_REF)
+    return NULL_TREE;
+  field = TREE_OPERAND (exp, 1);
+  if (TREE_CODE (field) != FIELD_DECL || !DECL_C_BIT_FIELD (field))
+    return NULL_TREE;
+  if (same_type_ignoring_top_level_qualifiers_p
+      (TREE_TYPE (exp), DECL_BIT_FIELD_TYPE (field)))
+    return NULL_TREE;
+  return DECL_BIT_FIELD_TYPE (field);
+}
+
 /* Perform the conversions in [expr] that apply when an lvalue appears
    in an rvalue context: the lvalue-to-rvalue, array-to-pointer, and
    function-to-pointer conversions.
 
-   In addition manifest constants are replaced by their values.  */
+   In addition, manifest constants are replaced by their values, and
+   bitfield references are converted to their declared types.  */
 
 tree
 decay_conversion (tree exp)
 {
   tree type;
+  tree bitfield_type;
   enum tree_code code;
 
   type = TREE_TYPE (exp);
-  code = TREE_CODE (type);
-
   if (type == error_mark_node)
     return error_mark_node;
 
@@ -1422,11 +1448,15 @@ decay_conversion (tree exp)
       return error_mark_node;
     }
 
+  bitfield_type = is_bitfield_expr_with_lowered_type (exp);
+  if (bitfield_type) 
+    exp = build_nop (bitfield_type, exp);
+
   exp = decl_constant_value (exp);
 
   /* build_c_cast puts on a NOP_EXPR to make the result not an lvalue.
      Leave such NOP_EXPRs, since RHS is being used in non-lvalue context.  */
-
+  code = TREE_CODE (type);
   if (code == VOID_TYPE)
     {
       error ("void value not ignored as it ought to be");
@@ -5500,11 +5530,9 @@ build_modify_expr (tree lhs, enum tree_code modifycode, tree rhs)
 
 	cond = build_conditional_expr
 	  (TREE_OPERAND (lhs, 0),
-	   build_modify_expr (cp_convert (TREE_TYPE (lhs),
-					  TREE_OPERAND (lhs, 1)),
+	   build_modify_expr (TREE_OPERAND (lhs, 1),
 			      modifycode, rhs),
-	   build_modify_expr (cp_convert (TREE_TYPE (lhs),
-					  TREE_OPERAND (lhs, 2)),
+	   build_modify_expr (TREE_OPERAND (lhs, 2),
 			      modifycode, rhs));
 
 	if (cond == error_mark_node)
diff --git a/gcc/print-tree.c b/gcc/print-tree.c
index 02e5c7b9c61..eed02f235f6 100644
--- a/gcc/print-tree.c
+++ b/gcc/print-tree.c
@@ -458,6 +458,9 @@ print_node (FILE *file, const char *prefix, tree node, int indent)
 	  print_node (file, "offset", DECL_FIELD_OFFSET (node), indent + 4);
 	  print_node (file, "bit offset", DECL_FIELD_BIT_OFFSET (node),
 		      indent + 4);
+	  if (DECL_BIT_FIELD_TYPE (node))
+	    print_node (file, "bit_field_type", DECL_BIT_FIELD_TYPE (node),
+			indent + 4);
 	}
 
       print_node_brief (file, "context", DECL_CONTEXT (node), indent + 4);
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 7a3fb0077a0..f0c3a5d5e0a 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,17 @@
+2006-04-23  Mark Mitchell  <mark@codesourcery.com>
+
+	PR c++/26534
+	* g++.dg/opt/bitfield1.C: New test.
+	* g++.dg/compat/abi/bitfield1_main.C: Add -w.
+	* g++.dg/compat/abi/bitfield1_x.C: Likewise.
+	* g++.dg/compat/abi/bitfield1_y.C: Likewise.
+	* g++.dg/compat/abi/bitfield2_main.C: Likewise.
+	* g++.dg/compat/abi/bitfield2_x.C: Likewise.
+	* g++.dg/compat/abi/bitfield2_y.C: Likewise.
+	* g++.dg/abi/bitfield1.C: Add dg-warning markers.
+	* g++.dg/abi/bitfield2.C: Likewise.
+	* g++.dg/init/bitfield1.C: Likewise.
+
 2006-04-23  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/25099
diff --git a/gcc/testsuite/g++.dg/abi/bitfield1.C b/gcc/testsuite/g++.dg/abi/bitfield1.C
index c707c85d82b..d5d04bcd73a 100644
--- a/gcc/testsuite/g++.dg/abi/bitfield1.C
+++ b/gcc/testsuite/g++.dg/abi/bitfield1.C
@@ -19,7 +19,7 @@ int main ()
 {
   A a;
 
-  a.bitS = 1;
+  a.bitS = 1; // { dg-warning "overflow" }
   a.bitU = 1;
   a.bit = 1;
 
diff --git a/gcc/testsuite/g++.dg/abi/bitfield2.C b/gcc/testsuite/g++.dg/abi/bitfield2.C
index d4d1d582649..452861ec29a 100644
--- a/gcc/testsuite/g++.dg/abi/bitfield2.C
+++ b/gcc/testsuite/g++.dg/abi/bitfield2.C
@@ -19,9 +19,9 @@ int main ()
 {
   A a;
 
-  a.bitS = 1;
+  a.bitS = 1; // { dg-warning "overflow" }
   a.bitU = 1;
-  a.bit = 1;
+  a.bit = 1;  // { dg-warning "overflow" }
 
   if (a.bitS != -1)
     return 1;
diff --git a/gcc/testsuite/g++.dg/compat/abi/bitfield1_main.C b/gcc/testsuite/g++.dg/compat/abi/bitfield1_main.C
index cdb7a45a744..ce9aa1f09ad 100644
--- a/gcc/testsuite/g++.dg/compat/abi/bitfield1_main.C
+++ b/gcc/testsuite/g++.dg/compat/abi/bitfield1_main.C
@@ -1,4 +1,4 @@
-// { dg-options "-ansi -pedantic-errors -funsigned-bitfields" }
+// { dg-options "-w -ansi -pedantic-errors -funsigned-bitfields" }
 
 // Copyright (C) 2001 Free Software Foundation, Inc.
 // Contributed by Nathan Sidwell 15 Dec 2001 <nathan@codesourcery.com>
diff --git a/gcc/testsuite/g++.dg/compat/abi/bitfield1_x.C b/gcc/testsuite/g++.dg/compat/abi/bitfield1_x.C
index e081c4bc943..727632af89d 100644
--- a/gcc/testsuite/g++.dg/compat/abi/bitfield1_x.C
+++ b/gcc/testsuite/g++.dg/compat/abi/bitfield1_x.C
@@ -1,4 +1,4 @@
-// { dg-options "-ansi -pedantic-errors -funsigned-bitfields" }
+// { dg-options "-w -ansi -pedantic-errors -funsigned-bitfields" }
 
 #include "bitfield1.h"
 
diff --git a/gcc/testsuite/g++.dg/compat/abi/bitfield1_y.C b/gcc/testsuite/g++.dg/compat/abi/bitfield1_y.C
index 10581dab0a4..28277671825 100644
--- a/gcc/testsuite/g++.dg/compat/abi/bitfield1_y.C
+++ b/gcc/testsuite/g++.dg/compat/abi/bitfield1_y.C
@@ -1,4 +1,4 @@
-// { dg-options "-ansi -pedantic-errors -funsigned-bitfields" }
+// { dg-options "-w -ansi -pedantic-errors -funsigned-bitfields" }
 
 extern "C" void abort (void);
 
diff --git a/gcc/testsuite/g++.dg/compat/abi/bitfield2_main.C b/gcc/testsuite/g++.dg/compat/abi/bitfield2_main.C
index df74037b66b..4169843f93e 100644
--- a/gcc/testsuite/g++.dg/compat/abi/bitfield2_main.C
+++ b/gcc/testsuite/g++.dg/compat/abi/bitfield2_main.C
@@ -1,4 +1,4 @@
-// { dg-options "-ansi -pedantic-errors -fsigned-bitfields" }
+// { dg-options "-w -ansi -pedantic-errors -fsigned-bitfields" }
 
 // Copyright (C) 2001 Free Software Foundation, Inc.
 // Contributed by Nathan Sidwell 15 Dec 2001 <nathan@codesourcery.com>
diff --git a/gcc/testsuite/g++.dg/compat/abi/bitfield2_x.C b/gcc/testsuite/g++.dg/compat/abi/bitfield2_x.C
index 47b448dda26..080d21b41ea 100644
--- a/gcc/testsuite/g++.dg/compat/abi/bitfield2_x.C
+++ b/gcc/testsuite/g++.dg/compat/abi/bitfield2_x.C
@@ -1,4 +1,4 @@
-// { dg-options "-ansi -pedantic-errors -fsigned-bitfields" }
+// { dg-options "-w -ansi -pedantic-errors -fsigned-bitfields" }
 
 #include "bitfield1.h"
 
diff --git a/gcc/testsuite/g++.dg/compat/abi/bitfield2_y.C b/gcc/testsuite/g++.dg/compat/abi/bitfield2_y.C
index 55edab5cbfe..d2757832861 100644
--- a/gcc/testsuite/g++.dg/compat/abi/bitfield2_y.C
+++ b/gcc/testsuite/g++.dg/compat/abi/bitfield2_y.C
@@ -1,4 +1,4 @@
-// { dg-options "-ansi -pedantic-errors -fsigned-bitfields" }
+// { dg-options "-w -ansi -pedantic-errors -fsigned-bitfields" }
 
 extern "C" void abort (void);
 
diff --git a/gcc/testsuite/g++.dg/init/bitfield1.C b/gcc/testsuite/g++.dg/init/bitfield1.C
index 786a116a562..70a06d0e144 100644
--- a/gcc/testsuite/g++.dg/init/bitfield1.C
+++ b/gcc/testsuite/g++.dg/init/bitfield1.C
@@ -14,11 +14,11 @@ void f ();
 int main ()
 {
   (f(), a.j) = 1;
-  (f(), a).j = 2;
-  (b ? a.j : a2.k) = 3;
+  (f(), a).j = 2; // { dg-warning "overflow" } 
+  (b ? a.j : a2.k) = 3; // { dg-warning "overflow" } 
   (b ? a : a2).j = 0;
   ++(a.j) = 1;
-  (a.j = 2) = 3;
+  (a.j = 2) = 3; // { dg-warning "overflow" } 
 }
 
     
diff --git a/gcc/testsuite/g++.dg/opt/bitfield1.C b/gcc/testsuite/g++.dg/opt/bitfield1.C
new file mode 100644
index 00000000000..49699961313
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/bitfield1.C
@@ -0,0 +1,18 @@
+// PR c++/26534
+// { dg-do run } 
+// { dg-options "-w -O2" }
+ 
+struct X
+{
+  unsigned a:4;
+};
+
+unsigned i;
+
+int main()
+{
+  struct X x = { 63u };
+  i = x.a;
+  if (i != 15)
+    return 1;
+}