Re: [PATCH] Pass correct memory attributes for build constant

[Kito Cheng <kito.cheng@gmail.com>]

For example in arm-elf-eabi, movmem need word align, otherwise it will
expand a libcall:

And gcc configure with "--target=arm-elf-eabi --disable-nls
--disable-shared --enable-languages=c,c++ --enable-threads=single
--enable-lto --with-newlib"

test.c:
extern bar(unsigned char p[3][2]);
void foo(int i)
{
    unsigned char data[3][2] = {{1,1}, {1,0}, {1,1}};

    bar(data);
}


Without this patch:
...
        .text
        .align  2
        .global foo
        .type   foo, %function
foo:
        @ Function supports interworking.
        @ args = 0, pretend = 0, frame = 8
        @ frame_needed = 0, uses_anonymous_args = 0
        str     lr, [sp, #-4]!
        sub     sp, sp, #12
        mov     r2, #6
        ldr     r1, .L3
        mov     r0, sp
        bl      memcpy @ LC0 has 4 byte align, but arm_gen_movmemqi
can't get right alignment info
        mov     r0, sp
        bl      bar
        add     sp, sp, #12
        @ sp needed
        ldr     lr, [sp], #4
        bx      lr
.L4:
        .align  2
.L3:
        .word   .LANCHOR0
        .size   foo, .-foo
        .section        .rodata
        .align  2
        .set    .LANCHOR0,. + 0
.LC0:
        .byte   1
        .byte   1
        .byte   1
        .byte   0
        .byte   1
        .byte   1


With this patch:

...
foo:
        @ Function supports interworking.
        @ args = 0, pretend = 0, frame = 8
        @ frame_needed = 0, uses_anonymous_args = 0
        str     lr, [sp, #-4]!
        ldr     r3, .L3 @ LC0 has 4 byte align, arm_gen_movmemqi get
right alignment info, so expand it!
        ldmia   r3, {r0, r1}
        sub     sp, sp, #12
        str     r0, [sp]
        mov     r0, sp
        strh    r1, [sp, #4]    @ movhi
        bl      bar
        add     sp, sp, #12
        @ sp needed
        ldr     lr, [sp], #4
        bx      lr
...

On Thu, Jun 26, 2014 at 5:01 AM, Jeff Law <law@redhat.com> wrote:
> On 06/25/14 09:35, Kito Cheng wrote:
>>
>> Hi all:
>>    This patch is fix constant memory's symbol_ref don't have right
>> alignment info since `exp` don't set alignment (and should not set
>> alignment info for `exp`)  , use `decl` to set_mem_attributes for
>> right alignment info.
>>
>> ChangLog
>> 2014-06-25  Kito Cheng  <kito@0xlab.org>
>>
>>          * varasm.c (build_constant_desc): Use decl to set mem
>>          attributes since exp don't have correct aligment info.
>
> Do you have a testcase for this?
>
> jeff
>