[committed] Unbreak big-endian bootstrap (PR middle-end/22141)

[Jakub Jelinek]

Hi!

Apparently I broke bootstrap or testing on big-endian targets,
I'm sorry for screwing up testing and not testing on any big-endian.

I've committed the following patch which fixes miscompilation on the
following short testcase:

struct S { char a, b, c, d; } s;
struct T { int a : 2, b : 5, c : 17, d : 8; } t, t2;

__attribute__((noipa)) void
foo (void)
{
  s.a = 1;
  s.b = 2;
  s.c = 3;
  s.d = 4;
}

__attribute__((noipa)) void
bar (void)
{
  t.a = 1;
  t.b = 2;
  t.c = 3;
  t.d = 4;
}

__attribute__((noipa)) void
baz (void)
{
  t.a = -2;
  t.c = 7;
  t.d = 8;
}

int
main ()
{
  foo ();
  if (s.a != 1 || s.b != 2 || s.c != 3 || s.d != 4)
    __builtin_abort ();
  bar ();
  if (t.a != 1 || t.b != 2 || t.c != 3 || t.d != 4)
    __builtin_abort ();
  baz ();
  if (t.a != -2 || t.b != 2 || t.c != 7 || t.d != 8)
    __builtin_abort ();
  __builtin_memset (&t, 0, sizeof (t));
  baz ();
  if (t.a != -2 || t.b != 0 || t.c != 7 || t.d != 8)
    __builtin_abort ();
  __builtin_memset (&t, -1, sizeof (t));
  baz ();
  if (t.a != -2 || t.b != -1 || t.c != 7 || t.d != 8)
    __builtin_abort ();
  return 0;
}

as obvious to unbreak bootstrap.  David said his AIX bootstrap is past
the bootstrap failure point now with this change.

2017-10-30  Jakub Jelinek  <ja...@redhat.com>

        PR middle-end/22141
        * gimple-ssa-store-merging.c (merged_store_group::apply_stores): Fix
        arguments to clear_bit_region_be.

--- gcc/gimple-ssa-store-merging.c.jj   2017-10-30 12:03:56.601219516 +0100
+++ gcc/gimple-ssa-store-merging.c      2017-10-30 17:03:55.713149323 +0100
@@ -701,7 +701,9 @@ merged_store_group::apply_stores ()
        return false;
       unsigned char *m = mask + (pos_in_buffer / BITS_PER_UNIT);
       if (BYTES_BIG_ENDIAN)
-       clear_bit_region_be (m, pos_in_buffer % BITS_PER_UNIT, info->bitsize);
+       clear_bit_region_be (m, (BITS_PER_UNIT - 1
+                                - (pos_in_buffer % BITS_PER_UNIT)),
+                            info->bitsize);
       else
        clear_bit_region (m, pos_in_buffer % BITS_PER_UNIT, info->bitsize);
     }

        Jakub