[PATCH] Fix endianness assumption in LRA

[David Miller]

This was the most glaring case, and would result in LRA crashing
if this code snippet was actually hit on big-endian, since
simplify_gen_subreg() will return NULL in such a case and then
we try to blindly emit a move to 'subreg'.

There is code in match_reload which seems to have a similar problem,
specifically these sequences:

          if (SCALAR_INT_MODE_P (inmode))
            new_out_reg = gen_lowpart_SUBREG (outmode, reg);
          else
            new_out_reg = gen_rtx_SUBREG (outmode, reg, 0);
 ...
          if (SCALAR_INT_MODE_P (outmode))
            new_in_reg = gen_lowpart_SUBREG (inmode, reg);
          else
            new_in_reg = gen_rtx_SUBREG (inmode, reg, 0);

But I have not tried to address those cases in this patch.

Vlad, is this OK to commit?

2015-09-14  David S. Miller  <da...@davemloft.net>

        * lra-constraints.c (simplify_operand_subreg): Do not assume that
        lowpart of a SUBREG has offset zero.

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index cdb2695..fc8e43d 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -1545,7 +1545,7 @@ simplify_operand_subreg (int nop, machine_mode reg_mode)
          bool insert_before, insert_after;
 
          PUT_MODE (new_reg, mode);
-          subreg = simplify_gen_subreg (innermode, new_reg, mode, 0);
+          subreg = gen_lowpart_SUBREG (innermode, new_reg);
          bitmap_set_bit (&lra_subreg_reload_pseudos, REGNO (new_reg));
 
          insert_before = (type != OP_OUT);