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by craftkiller16 hours ago |
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upvoteby metabagel16 hours ago|
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From the article:

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Should you go branchless?

Most of the time, no. Branchless code is harder to read and easier to get wrong. Besides, compilers know a lot of tricks and already do a lot of this work for us.

Only when a profiler points at a hot loop, and the loop contains a branch on unpredictable data this technique can pay off big.

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upvoteby metabagel16 hours ago|
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OK, but the code with the branch is easier to understand.
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upvoteby robby_w_g16 hours ago|
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Yeah, I don't buy the premise that branchless code is intrinsically easier to understand. Maybe OP's point is that adding unnecessary branches makes code harder to read? But that's generally the case for any unnecessary code.
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upvoteby winternewt15 hours ago|
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I see stuff along the lines of:

  if (x == 0) {
      return y;
  }
  
  y += 25*x;
  return y;
and skipping the if just makes the function shorter and simpler, while also not involving the CPU branch prediction. Another one that doesn't necessarily skip all branching but at least drops one - and more importantly makes the code simpler and easy to verify, is removing the if statement in code like

  if (count == 0) {
      return;
  }

  for (int i = 0; i != count; i++) {
    puts("hello");
  }
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upvoteby GuB-4210 hours ago|
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Both of your examples are optimized by the compiler (gcc 16.1 -O3).

In the first case, the compiler removes the first if/return

In the second case, if you don't have the first if/return the compiler will add it. That's because it will actually convert your loop into a do/while, with the test in the end, because it is more efficient. But it has to handle the count == 0 special case first, so it will do that early return even if it is not explicitly there.

That's the kind of optimization modern compilers are good at.

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upvoteby jamiejquinn16 hours ago|
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Generally agree. As with many optimisations, branchless code can easily be less obvious than the branchy equivalent.
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upvoteby cestith16 hours ago|
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That's a really nice example. Thanks.
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