Cmp peephole optimization isn't always safe for signed arithmetics.

int tries = INT_MAX;    
while (tries > 0) {
      tries--;
}

The check should be:
        subs    r4, #1
        cmp     r4, #0
        bgt     LBB0_1

The subs can set the overflow V bit when r4 is INT_MAX+1 (which loop
canonicalization apparently does in this case). cmp #0 would have cleared
it while not changing the N and Z bits. Since BGT is dependent on the V
bit, i.e. (N == V) && !Z, it is not safe to eliminate the cmp #0.

rdar://9172742


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128179 91177308-0d34-0410-b5e6-96231b3b80d8

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