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>Now you're just being intentionally obtuse. When I write if (x) y += z and say that it should be implemented with conditional moves or predicated adds per your

>Now you're just being intentionally obtuse. When I write if (x) y += z and say that it should be implemented with conditional moves or predicated adds per your platform, there really isn't much room for confusion. May be I am obtuse though not intentionally. If you wanted to say that if's can be replaced with predicated instructions why such a convoluted example (which is a nice piece of code, by the way)? >Actually, all modern desktop-class GPU architectures have branch instructions. Indeed, and as you say, they are not always executed because a single SIMD core executes threads in a lock-step and it's only possible to branch when all the threads yield the same condition. Besides there are still GPUs without branches, e.g. PS3 fragment shaders.

psykotic 15y ago
> If you wanted to say that if's can be replaced with predicated instructions why such a convoluted example (which is a nice piece of code, by the way)? That's not what I wanted to say; it was a side note to a piece of code. Anyway, sorry if it was confusing. It was a spur-of-the-moment comment on Hacker News, not a carefully wrought essay. > Besides there are still GPUs without branches, e.g. PS3 fragment shaders. The RSX is ancient at this point, a turd in a box. It was a turd even at the time when, in the eleventh hour of the PS3 project, Sony begged NVIDIA to give them a GPU after their fantasy of Cell-based rasterization had proved ludicrous. It's so bad that you have to offload a ton of work on the SPUs to get acceptable graphics performance.