[Bug target/45039] New: memory access and address update in one instruction for thumb2

[carrot at google dot com]

Compile following code with options -march=armv7-a -mthumb -Os

char* tq(char* p, char c1, char c2)
{
  *p++ = c1;
  *p++ = c2;
  return p;
}

GCC 4.6 generates

        strb    r1, [r0, #0]
        strb    r2, [r0, #1]
        adds    r0, r0, #2
        bx      lr

It can be simplified to:

        strb    r2, [r0, #1]
        strb    r1, [r0], #2
        bx      lr

If I change the option -Os to -O2, the result is worse:

        mov     r3, r0
        adds    r0, r0, #2
        strb    r1, [r3, #0]
        strb    r2, [r3, #1]
        bx      lr


-- 
           Summary: memory access and address update in one instruction for
                    thumb2
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: carrot at google dot com
 GCC build triplet: i686-linux
  GCC host triplet: i686-linux
GCC target triplet: arm-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45039