[PATCH] fix arm neon ICE by widening tree_type's precision field

[Nathan Froyd <froydnj@codesourcery.com>]

ARM's NEON support in GCC includes some rather wide types: XImode, the
biggest, is a 64-byte integer type.  Compiling the simple testcase in
the patch below, which uses XImode, results in an ICE.

The reason behind this is because XImode is defined as a
FRACTIONAL_INT_MODE of 511 bits, rather than an INT_MODE of 64 bytes.
This hack was done because the 'precision' field of tree_type is only 9
bits wide...and therefore can't store XImode's actual precision of 512
bits.  So when we ask mode_for_size for a MODE_INT of 512 bits, it
thinks that the only reasonable choice is BLKmode--since XImode is not
a MODE_INT mode.  We eventually wind up calling simplify_subreg with the
input mode of BLKmode, which triggers an ICE.

The fix is to widen the 'precision' field of tree_type to 10 bits.
Unfortunately, there's not much space in tree_type to widen that field;
the structure is nicely packed for 32-bit and 64-bit hosts.  The
approach I've taken in the patch below is to move packed_flag into
tree_base and rearrange the bitfields in tree_type.  I realize this is
slightly gross, but I don't see a better way--suggestions welcome.

Tested with cross to arm-none-eabi.  OK to commit?  (Need middle-end
approval for the tree.h changes and ARM approval for arm-modes.def.)

-Nathan

2009-06-08  Nathan Froyd  <froydnj@codesourcery.com>

	* tree.h (tree_base): Add packed_flag, moved from...
	(tree_type): ...here.  Widen precision field to 10 bits and
	rearrange fields to pack nicely.
	(TYPE_PACKED): Update for new location of packed_flag.
	* config/arm/arm-modes.def (XImode): Define as a INT_MODE.

Index: config/arm/arm-modes.def
===================================================================
--- config/arm/arm-modes.def	(revision 148220)
+++ config/arm/arm-modes.def	(working copy)
@@ -62,6 +62,4 @@ VECTOR_MODES (FLOAT, 16);     /*       V
 INT_MODE (EI, 24);
 INT_MODE (OI, 32);
 INT_MODE (CI, 48);
-/* ??? This should actually have 512 bits but the precision only has 9
-   bits.  */
-FRACTIONAL_INT_MODE (XI, 511, 64);
+INT_MODE (XI, 64);
Index: testsuite/ChangeLog
===================================================================
--- testsuite/ChangeLog	(revision 148220)
+++ testsuite/ChangeLog	(working copy)
@@ -1,3 +1,7 @@
+2009-06-08  Nathan Froyd  <froydnj@codesourcery.com>
+
+	* gcc.target/arm/neon-dse-1.c: New test.
+
 2009-06-05  Jakub Jelinek  <jakub@redhat.com>
 
 	PR middle-end/40340
Index: testsuite/gcc.target/arm/neon-dse-1.c
===================================================================
--- testsuite/gcc.target/arm/neon-dse-1.c	(revision 0)
+++ testsuite/gcc.target/arm/neon-dse-1.c	(revision 0)
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_neon_ok } */
+/* { dg-options "-O1" } */
+/* { dg-add-options arm_neon } */
+
+#include <arm_neon.h>
+
+void neon_internal_error(int *dst, int *src)
+{
+  uint16x8x4_t sval;
+
+  sval = vld4q_u16((void *)src);
+  vst4q_u16((void *)dst,sval);
+}
Index: tree.h
===================================================================
--- tree.h	(revision 148220)
+++ tree.h	(working copy)
@@ -373,8 +373,10 @@ struct GTY(()) tree_base {
   unsigned lang_flag_6 : 1;
 
   unsigned visited : 1;
+  /* For tree_type.  */
+  unsigned packed_flag : 1;
 
-  unsigned spare : 23;
+  unsigned spare : 22;
 
   union tree_ann_d *ann;
 };
@@ -2219,7 +2221,7 @@ extern enum machine_mode vector_type_mod
 
 /* Indicated that objects of this type should be laid out in as
    compact a way as possible.  */
-#define TYPE_PACKED(NODE) (TYPE_CHECK (NODE)->type.packed_flag)
+#define TYPE_PACKED(NODE) (TYPE_CHECK (NODE)->common.base.packed_flag)
 
 /* Used by type_contains_placeholder_p to avoid recomputation.
    Values are: 0 (unknown), 1 (false), 2 (true).  Never access
@@ -2237,17 +2239,16 @@ struct GTY(()) tree_type {
   tree attributes;
   unsigned int uid;
 
-  unsigned int precision : 9;
-  ENUM_BITFIELD(machine_mode) mode : 7;
-
-  unsigned string_flag : 1;
+  unsigned int precision : 10;
   unsigned no_force_blk_flag : 1;
   unsigned needs_constructing_flag : 1;
   unsigned transparent_union_flag : 1;
-  unsigned packed_flag : 1;
   unsigned restrict_flag : 1;
   unsigned contains_placeholder_bits : 2;
 
+  ENUM_BITFIELD(machine_mode) mode : 7;
+  unsigned string_flag : 1;
+
   unsigned lang_flag_0 : 1;
   unsigned lang_flag_1 : 1;
   unsigned lang_flag_2 : 1;