* stor-layout.c (update_alignment_for_field): Correct handling of

	unnamed bitfields on PCC_BITFIELD_TYPE_MATTERS machines.
	* doc/tm.texi (PCC_BITFIELD_TYPE_MATTERS): Note that an unnamed
	bitfield does not affect alignment.

	* testsuite/gcc.dg/i386-bitfield3.c: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@60439 138bc75d-0d04-0410-961f-82ee72b054a4

5 files changed, 62 insertions, 20 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index d066b2811db..607b179155e 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2002-12-23  Mark Mitchell  <mark@codesourcery.com>
+
+	* stor-layout.c (update_alignment_for_field): Correct handling of
+	unnamed bitfields on PCC_BITFIELD_TYPE_MATTERS machines.
+	* doc/tm.texi (PCC_BITFIELD_TYPE_MATTERS): Note that an unnamed
+	bitfield does not affect alignment.
+
 2002-12-23  David Edelsohn  <edelsohn@gnu.org>
 
 	* expr.c (expand_assignment): Apply special treatment to
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 496a4a298dd..8436e899666 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -1181,17 +1181,19 @@ go slower in that case, define this macro as 0.
 Define this if you wish to imitate the way many other C compilers handle
 alignment of bit-fields and the structures that contain them.
 
-The behavior is that the type written for a bit-field (@code{int},
-@code{short}, or other integer type) imposes an alignment for the
-entire structure, as if the structure really did contain an ordinary
-field of that type.  In addition, the bit-field is placed within the
-structure so that it would fit within such a field, not crossing a
-boundary for it.
-
-Thus, on most machines, a bit-field whose type is written as @code{int}
-would not cross a four-byte boundary, and would force four-byte
-alignment for the whole structure.  (The alignment used may not be four
-bytes; it is controlled by the other alignment parameters.)
+The behavior is that the type written for a named bit-field (@code{int},
+@code{short}, or other integer type) imposes an alignment for the entire
+structure, as if the structure really did contain an ordinary field of
+that type.  In addition, the bit-field is placed within the structure so
+that it would fit within such a field, not crossing a boundary for it.
+
+Thus, on most machines, a named bit-field whose type is written as
+@code{int} would not cross a four-byte boundary, and would force
+four-byte alignment for the whole structure.  (The alignment used may
+not be four bytes; it is controlled by the other alignment parameters.)
+
+An unnamed bit-field will not affect the alignment of the containing
+structure.
 
 If the macro is defined, its definition should be a C expression;
 a nonzero value for the expression enables this behavior.
diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
index c4fdaeeb91e..6c81924b69d 100644
--- a/gcc/stor-layout.c
+++ b/gcc/stor-layout.c
@@ -715,13 +715,9 @@ update_alignment_for_field (rli, field, known_align)
       && DECL_BIT_FIELD_TYPE (field)
       && ! integer_zerop (TYPE_SIZE (type)))
     {
-      /* For these machines, a zero-length field does not
-	 affect the alignment of the structure as a whole.
-	 It does, however, affect the alignment of the next field
-	 within the structure.  */
-      if (! integer_zerop (DECL_SIZE (field)))
-	rli->record_align = MAX (rli->record_align, desired_align);
-      else if (! DECL_PACKED (field))
+      /* A zero-length bit-field affects the alignment of the next
+	 field.  */
+      if (!DECL_PACKED (field) && integer_zerop (DECL_SIZE (field)))
 	{
 	  desired_align = TYPE_ALIGN (type);
 #ifdef ADJUST_FIELD_ALIGN
@@ -729,8 +725,8 @@ update_alignment_for_field (rli, field, known_align)
 #endif
 	}
 
-      /* A named bit field of declared type `int'
-	 forces the entire structure to have `int' alignment.  */
+      /* Named bit-fields cause the entire structure to have the
+	 alignment implied by their type.  */
       if (DECL_NAME (field) != 0)
 	{
 	  unsigned int type_align = TYPE_ALIGN (type);
@@ -745,7 +741,14 @@ update_alignment_for_field (rli, field, known_align)
 	  else if (DECL_PACKED (field))
 	    type_align = MIN (type_align, BITS_PER_UNIT);
 
+	  /* The alignment of the record is increased to the maximum
+	     of the current alignment, the alignment indicated on the
+	     field (i.e., the alignment specified by an __aligned__
+	     attribute), and the alignment indicated by the type of
+	     the field.  */
+	  rli->record_align = MAX (rli->record_align, desired_align);
 	  rli->record_align = MAX (rli->record_align, type_align);
+
 	  rli->unpadded_align = MAX (rli->unpadded_align, DECL_ALIGN (field));
 	  if (warn_packed)
 	    rli->unpacked_align = MAX (rli->unpacked_align, TYPE_ALIGN (type));
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index db2e5f57900..c4011100dac 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2002-12-23  Mark Mitchell  <mark@codesourcery.com>
+
+	* testsuite/gcc.dg/i386-bitfield3.c: New test.
+	
+	* testsuite/gcc.dg/i386-bitfield2.c: New test.
+	
 2002-12-22  Nathan Sidwell  <nathan@codesourcery.com>
 
 	* g++.dg/parse/conv_op1.C: New test.
diff --git a/gcc/testsuite/gcc.dg/i386-bitfield3.c b/gcc/testsuite/gcc.dg/i386-bitfield3.c
new file mode 100644
index 00000000000..781c2f7ba4e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/i386-bitfield3.c
@@ -0,0 +1,24 @@
+// Test for bitfield alignment in structs on IA-32
+// { dg-do run { target i?86-*-* } }
+// { dg-options "-O2" }
+// { dg-options "-mno-align-double -mno-ms-bitfields" { target *-*-interix* } }
+
+extern void abort (void);
+extern void exit (int);
+
+struct X {
+  int : 32;
+};
+
+struct Y {
+  int i : 32;
+};
+
+int main () {
+  if (__alignof__(struct X) != 1)
+    abort ();
+  if (__alignof__(struct Y) != 4)
+    abort ();
+  
+  exit (0);
+}