[Bug target/43723] New: Some ARMs support unaligned

[astrange at ithinksw dot com]

Source:
struct s { int i; } __attribute__((packed));

int a(struct s *s)
{
    return s->i;
}

Using 4.5:
> /usr/local/gcc-arm/bin/arm-none-linux-gnueabi-gcc -Os -mcpu=cortex-a8 -S unaligned.c
> cat unaligned.s
        .cpu cortex-a8
        .fpu softvfp
        .eabi_attribute 20, 1
        .eabi_attribute 21, 1
        .eabi_attribute 23, 3
        .eabi_attribute 24, 1
        .eabi_attribute 25, 1
        .eabi_attribute 26, 2
        .eabi_attribute 30, 4
        .eabi_attribute 18, 4
        .file   "unaligned.c"
        .text
        .align  2
        .global a
        .type   a, %function
a:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        ldrb    r2, [r0, #1]    @ zero_extendqisi2
        ldrb    r3, [r0, #0]    @ zero_extendqisi2
        orr     r3, r3, r2, asl #8
        ldrb    r2, [r0, #2]    @ zero_extendqisi2
        ldrb    r0, [r0, #3]    @ zero_extendqisi2
        orr     r3, r3, r2, asl #16
        orr     r0, r3, r0, asl #24
        bx      lr
        .size   a, .-a
        .ident  "GCC: (GNU) 4.5.0 20100325 (experimental)"
        .section        .note.GNU-stack,"",%progbits

At least some configurations of cortex-a8 support unaligned access just fine,
so it should be possible to use it. But it doesn't look like it is - there is
no -mno-strict-align for arm. This would be a major code size reduction for
FFmpeg.


-- 
           Summary: Some ARMs support unaligned
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: astrange at ithinksw dot com
GCC target triplet: arm-unknown-linux-gnueabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43723