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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/64306] [SH] Improve unaligned loads and stores
Date: Sun, 22 Feb 2015 14:44:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64306

Oleg Endo <olegendo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-02-22
     Ever confirmed|0                           |1

--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> ---
When storing bswapped values to unaligned mems the following happens:

union unaligned32s { int val; } __attribute__((packed));

void store_32s_0 (unsigned char* x, unsigned char a, int b)
{
  ((union unaligned32s*)(x))->val = a;
}

        mov     #0,r0
        extu.b  r5,r5
        mov.b   r0,@(1,r4)
        mov.b   r0,@(2,r4)
        mov     r5,r0        // r0 = zero (redundant load)
        shlr16  r0           // 0 >> 16 (redundant shift)
        mov.b   r5,@r4
        shlr8   r0           // 0 >> 8 (redundant shift)
        rts
        mov.b   r0,@(3,r4)

should be:
        mov.b   r5,@r4
        mov     #0,r0
        mov.b   r0,@(1,r4)
        mov.b   r0,@(2,r4)
        mov.b   r0,@(3,r4)



void store_32s_1 (unsigned char* x, unsigned char a, int b)
{
  ((union unaligned32s*)(x))->val = __builtin_bswap32 (a);
}

    extu.b  r5,r5
    swap.b  r5,r5
    swap.w  r5,r5
    extu.b  r5,r1
    mov.b   r1,@r4
    mov     #0,r1
    mov     r1,r0
    mov.b   r0,@(1,r4)
    mov.b   r0,@(2,r4)
    mov     r5,r0
    shlr16  r0
    shlr8   r0
    rts
    mov.b   r0,@(3,r4)


should be:
        mov     #0,r0
        mov.b   r0,@(0,r4)
        mov.b   r0,@(1,r4)
        mov.b   r0,@(2,r4)
        mov     r5,r0
        mov.b   r0,@(3,r4)

A similar thing happens when storing the T bit to unaligned mems, see also PR
65162.