[Bug target/50750] New: SH Target: Pre-decrement addressing used only for first memory access

["oleg dot endo at t-online dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50750

             Bug #: 50750
           Summary: SH Target: Pre-decrement addressing used only for
                    first memory access
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: oleg.endo@t-online.de
                CC: kkojima@gcc.gnu.org
            Target: sh*-*-*


Pre-decrement addressing is generated only for the first
memory access. Any subsequent memory access does not use 
pre-decrement addressing.
The following is a reduced example.
The problem exists with any number of memory accesses > 1
and at any optimization level.


int test_func_2_1 (int* p, int c)
{
  int r = 0;
  do
  {
    r += *--p;
    r += *--p;
    r += *--p;
  } while (--c);
  return r;
}

compiled with -fno-tree-loop-optimize -Os -m4-single -ml:

    mov    #0,r0
.L11:
    mov    r4,r1
    add    #-64,r1
    mov.l    @(60,r1),r2
    dt    r5
    add    #-12,r4
    add    r2,r0
    mov.l    @(56,r1),r2
    mov.l    @(52,r1),r1
    add    r2,r0
    bf/s    .L11
    add    r1,r0
    rts    
    nop


would be better as:

    mov    #0,r0
.L11:
    mov.l    @-r4,r1
    dt    r5
    mov.l    @-r4,r2
    add    r1,r0
    mov.l    @-r4,r3
    add    r2,r0
    bf/s    .L11
    add    r3,r0
    rts    
    nop



Using built-in specs.
COLLECT_GCC=sh-elf-gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/sh-elf/4.7.0/lto-wrapper
Target: sh-elf
Configured with: ../gcc-trunk/configure --target=sh-elf --prefix=/usr/local
--enable-languages=c,c++ --enable-multilib --disable-libssp --disable-nls
--disable-werror --enable-lto --with-newlib --with-gnu-as --with-gnu-ld
--with-system-zlib
Thread model: single
gcc version 4.7.0 20111016 (experimental) (GCC)