Question about GCC's standard dependent optimization

["Bin.Cheng" <amker dot cheng at gmail dot com>]

Hi,
I ran into PR60947, in which GCC understands the return value of
memset is the first argument passed in, according to standard, then
does optimization like below:
    mov    ip, sp
    stmfd    sp!, {r4, r5, r6, r7, r8, r9, r10, fp, ip, lr, pc}
    sub    fp, ip, #4
    sub    sp, sp, #20
    ldr    r8, [r0, #112]
    add    r3, r8, #232
    add    r4, r8, #328
.L1064:
    mov    r0, r3
    mov    r1, #255
    mov    r2, #8
    bl    memset
    add    r3, r0, #32   <----X
    cmp    r3, r4
    bne    .L1064

For X insn, GCC takes advantage of standard by using the returned r0 directly.

My question is, is it always safe for GCC to do such optimization?  Do
we have an option to disable such standard dependent optimization?

BTW, the sample should be further optimized into below (with Y redundant now):

    mov    ip, sp
    stmfd    sp!, {r4, r5, r6, r7, r8, r9, r10, fp, ip, lr, pc}
    sub    fp, ip, #4
    sub    sp, sp, #20
    ldr    r8, [r0, #112]
    add    r0, r8, #232
    add    r4, r8, #328
.L1064:
    mov    r0, r0       <------Y
    mov    r1, #255
    mov    r2, #8
    bl    memset
    add    r0, r0, #32
    cmp    r0, r4
    bne    .L1064


Thanks,
bin