Comment by fsmv

But it's not exactly a cosmetic change. x++ is semantically different from x; x++; I wonder if clang would make it branchless if you instead write

  if (BLQS_CMP(x, piv)) { *lwr = x; ++lwr; }
    else { *rwr = x; --rwr; }

The difference is post-increment has strange semantics. While the compiler should be able to understand that the value wasn't used and post increment and pre increment are the same I wouldn't be surprised if it tracks that it was post increment and misses some optimizations because it's trying to garuntee post increment semantics.

Although it's true compilers can be very sensitive to exact phrasing triggering specific optimization passes. So it still might not give the branchless version by changing it to pre increment (which is the same as a normal +=1).

The only way to really know is to dig into what optimization passes clang took in both cases and analyze the difference.