[PATCHv2] Clean up by_pieces_ninsns

[HAO CHEN GUI]

Hi,
  This patch cleans up by_pieces_ninsns and does following things.
1. Do the length and alignment adjustment for by pieces compare when
overlap operation is enabled.
2. Replace unnecessary mov_optab checks with gcc assertions.

  Compared to last version, the main change is to replace unnecessary
mov_optab checks with gcc assertions and fix the indentation.

  Bootstrapped and tested on x86 and powerpc64-linux BE and LE with
no regressions. Is this OK for trunk?

Thanks
Gui Haochen

ChangeLog
Clean up by_pieces_ninsns

The by pieces compare can be implemented by overlapped operations. So
it should be taken into consideration when doing the adjustment for
overlap operations.  The mode returned from
widest_fixed_size_mode_for_size is already checked with mov_optab in
by_pieces_mode_supported_p called by widest_fixed_size_mode_for_size.
So it is no need to check mov_optab again in by_pieces_ninsns.  The
patch fixes these issues.

gcc/
        * expr.cc (by_pieces_ninsns): Include by pieces compare when
        do the adjustment for overlap operations.  Replace mov_optab
        checks with gcc assertions.

patch.diff
diff --git a/gcc/expr.cc b/gcc/expr.cc
index 556bcf7ef59..ffd18fe43cc 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -1090,18 +1090,16 @@ by_pieces_ninsns (unsigned HOST_WIDE_INT l, unsigned 
int align,
   unsigned HOST_WIDE_INT n_insns = 0;
   fixed_size_mode mode;

-  if (targetm.overlap_op_by_pieces_p () && op != COMPARE_BY_PIECES)
+  if (targetm.overlap_op_by_pieces_p ())
     {
       /* NB: Round up L and ALIGN to the widest integer mode for
         MAX_SIZE.  */
       mode = widest_fixed_size_mode_for_size (max_size, op);
-      if (optab_handler (mov_optab, mode) != CODE_FOR_nothing)
-       {
-         unsigned HOST_WIDE_INT up = ROUND_UP (l, GET_MODE_SIZE (mode));
-         if (up > l)
-           l = up;
-         align = GET_MODE_ALIGNMENT (mode);
-       }
+      gcc_assert (optab_handler (mov_optab, mode) != CODE_FOR_nothing);
+      unsigned HOST_WIDE_INT up = ROUND_UP (l, GET_MODE_SIZE (mode));
+      if (up > l)
+       l = up;
+      align = GET_MODE_ALIGNMENT (mode);
     }

   align = alignment_for_piecewise_move (MOVE_MAX_PIECES, align);
@@ -1109,12 +1107,11 @@ by_pieces_ninsns (unsigned HOST_WIDE_INT l, unsigned 
int align,
   while (max_size > 1 && l > 0)
     {
       mode = widest_fixed_size_mode_for_size (max_size, op);
-      enum insn_code icode;
+      gcc_assert (optab_handler (mov_optab, mode) != CODE_FOR_nothing);

       unsigned int modesize = GET_MODE_SIZE (mode);

-      icode = optab_handler (mov_optab, mode);
-      if (icode != CODE_FOR_nothing && align >= GET_MODE_ALIGNMENT (mode))
+      if (align >= GET_MODE_ALIGNMENT (mode))
        {
          unsigned HOST_WIDE_INT n_pieces = l / modesize;
          l %= modesize;