PR middle-end/17112

	* stor-layout.c (compute_record_mode): For records with a single
	field, only use the field's mode if its size matches what we'd
	have choosen for the record ourselves.  This forces the use of
	BLKmode for packed records that don't completely fill a mode.

	* gcc.dg/pr17112-1.c: New test case.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@88130 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 53 insertions, 5 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index af865b18477..75ba5a7163f 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,4 +1,13 @@
 2004-09-26  Roger Sayle  <roger@eyesopen.com>
+	    Giovanni Bajo  <giovannibajo@gcc.gnu.org>
+
+	PR middle-end/17112
+	* stor-layout.c (compute_record_mode): For records with a single
+	field, only use the field's mode if its size matches what we'd
+	have choosen for the record ourselves.  This forces the use of
+	BLKmode for packed records that don't completely fill a mode.
+
+2004-09-26  Roger Sayle  <roger@eyesopen.com>
 
 	PR middle-end/17151
 	* combine.c (force_to_mode): Remove dubious early return test that
diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
index ccbca424bbf..4ac93404a8e 100644
--- a/gcc/stor-layout.c
+++ b/gcc/stor-layout.c
@@ -1296,12 +1296,14 @@ compute_record_mode (tree type)
 #endif /* MEMBER_TYPE_FORCES_BLK  */
     }
 
-  /* If we only have one real field; use its mode.  This only applies to
-     RECORD_TYPE.  This does not apply to unions.  */
-  if (TREE_CODE (type) == RECORD_TYPE && mode != VOIDmode)
+  TYPE_MODE (type) = mode_for_size_tree (TYPE_SIZE (type), MODE_INT, 1);
+
+  /* If we only have one real field; use its mode if that mode's size
+     matches the type's size.  This only applies to RECORD_TYPE.  This
+     does not apply to unions.  */
+  if (TREE_CODE (type) == RECORD_TYPE && mode != VOIDmode
+      && GET_MODE_SIZE (mode) == GET_MODE_SIZE (TYPE_MODE (type)))
     TYPE_MODE (type) = mode;
-  else
-    TYPE_MODE (type) = mode_for_size_tree (TYPE_SIZE (type), MODE_INT, 1);
 
   /* If structure's known alignment is less than what the scalar
      mode would need, and it matters, then stick with BLKmode.  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 32c3d51a555..f6ac25c0f07 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2004-09-26  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/17112
+	* gcc.dg/pr17112-1.c: New test case.
+
 2004-09-26  Joseph S. Myers  <jsm@polyomino.org.uk>
 
 	PR c/11459
diff --git a/gcc/testsuite/gcc.dg/pr17112-1.c b/gcc/testsuite/gcc.dg/pr17112-1.c
new file mode 100644
index 00000000000..7c8b7aa0432
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr17112-1.c
@@ -0,0 +1,32 @@
+/* PR middle-end/17112 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+extern void abort(void);
+
+typedef struct {
+  int int24:24  __attribute__ ((packed));
+} myint24;
+
+myint24 x[3] = {
+  0x123456,
+  0x789abc,
+  0xdef012
+};
+
+myint24 y[3];  // starts out as zeros
+
+void foo()
+{
+  y[1] = x[1];
+}
+
+int main()
+{
+  foo();
+
+  if (y[0].int24 != 0 || y[2].int24 != 0)
+    abort();
+  return 0;
+}
+