Re: [PATCH, ARM] Fix NEON vset_lane for D registers

[Julian Brown]

On Tue, 03 May 2011 15:49:38 +0100
Richard Earnshaw <rearn...@arm.com> wrote:

> 
> On Tue, 2011-05-03 at 13:49 +0100, Julian Brown wrote:
> > Hi,
> > 
> > This patch fixes vset_lane intrinsic variants for D-register sized
> > variables. A typo meant that the wrong lane would be set in many
> > circumstances.
> > 
> > Tested manually only. OK to apply?
> > 
> > Thanks,
> > 
> > Julian
> > 
> > ChangeLog
> > 
> >     gcc/
> >     * config/arm/neon.md (vec_set<mode>_internal): Fix misplaced
> >     parenthesis in D-register case.
> 
> Presumably this is a silent 'wrong-code' bug.  If so, what about
> released compilers?

Yes, this is a silent wrong-code bug. It affects branches back to at
gcc-4.4-branch at least: the patch will apply trivially to those, if
deemed appropriate (I think it's obvious enough to be risk-free).

Joseph wrote:

> And what about an execution testcase that fails before and passes
> after the patch?  Is it hard to add one for some reason?

I've added a testcase, and also done a regression run at Ramana's
request, which doesn't show up anything untoward.

So: OK to apply to trunk? Other branches? (Which?)

Thanks,

Julian

ChangeLog

    gcc/
    * config/arm/neon.md (vec_set<mode>_internal): Fix misplaced
    parenthesis in D-register case.

    gcc/testsuite/
    * gcc.target/arm/neon-vset_lanes8.c: New test.
Index: gcc/testsuite/gcc.target/arm/neon-vset_lanes8.c
===================================================================
--- gcc/testsuite/gcc.target/arm/neon-vset_lanes8.c	(revision 0)
+++ gcc/testsuite/gcc.target/arm/neon-vset_lanes8.c	(revision 0)
@@ -0,0 +1,21 @@
+/* Test the `vset_lane_s8' ARM Neon intrinsic.  */
+
+/* { dg-do run } */
+/* { dg-require-effective-target arm_neon_hw } */
+/* { dg-options "-O0" } */
+/* { dg-add-options arm_neon } */
+
+#include "arm_neon.h"
+#include <stdlib.h>
+#include <string.h>
+
+int8x8_t x = { 1, 2, 3, 4, 5, 6, 7, 8 };
+int8x8_t y = { 1, 2, 3, 16, 5, 6, 7, 8 };
+
+int main (void)
+{
+  x = vset_lane_s8 (16, x, 3);
+  if (memcmp (&x, &y, sizeof (x)) != 0)
+    abort();
+  return 0;
+}
Index: gcc/config/arm/neon.md
===================================================================
--- gcc/config/arm/neon.md	(revision 173299)
+++ gcc/config/arm/neon.md	(working copy)
@@ -426,7 +426,7 @@
           (match_operand:SI 2 "immediate_operand" "i")))]
   "TARGET_NEON"
 {
-  int elt = ffs ((int) INTVAL (operands[2]) - 1);
+  int elt = ffs ((int) INTVAL (operands[2])) - 1;
   if (BYTES_BIG_ENDIAN)
     elt = GET_MODE_NUNITS (<MODE>mode) - 1 - elt;
   operands[2] = GEN_INT (elt);