[Bug c/42046] New: missed optimization on ARM

["bruck dot michael at googlemail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

$ cat test.c

int     var;

void foo(int enable)
{
    if (enable)
        var |= 1;
    else
        var &= ~1;
}

$ arm-elf-gcc.exe -O6 -S test.c

$ cat test.s
        .file   "test.c"
        .text
        .align  2
        .global foo
        .type   foo, %function
foo:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        cmp     r0, #0
        ldrne   r3, .L4
        ldreq   r3, .L4
        ldrne   r2, [r3, #0]
        ldreq   r2, [r3, #0]
        orrne   r2, r2, #1
        biceq   r2, r2, #1
        strne   r2, [r3, #0]
        streq   r2, [r3, #0]
        bx      lr
.L5:
        .align  2
.L4:
        .word   var
        .size   foo, .-foo
        .comm   var,4,4
        .ident  "GCC: (GNU) 4.5.0 20091114 (experimental)"

This should be:
        cmp     r0, #0
        ldr     r3, .L4
        ldr     r2, [r3, #0]
        orrne   r2, r2, #1
        biceq   r2, r2, #1
        str     r2, [r3, #0]
        bx      lr

Interestingly -Os eliminates two of the three duplicates:

        ldr     r3, .L5
        cmp     r0, #0
        ldrne   r2, [r3, #0]
        ldreq   r2, [r3, #0]
        orrne   r2, r2, #1
        biceq   r2, r2, #1
        str     r2, [r3, #0]
        bx      lr


Due to inefficient cache use the -Os version will probably execute faster than
-O6.

This is built with svn revision 154184


-- 
           Summary: missed optimization on ARM
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bruck dot michael at googlemail dot com
 GCC build triplet: i686-pc-cygwin
  GCC host triplet: i686-pc-cygwin
GCC target triplet: arm-unknown-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42046