On 08/27/2011 11:29 AM, Linus Torvalds wrote:
On Sat, Aug 27, 2011 at 4:34 AM, Kamil Dudka<kdudka@xxxxxxxxxx> wrote:
Two years ago I proposed a patch that I believe would solve your problem:
https://patchwork.kernel.org/patch/40307/
Ack.
The sparse output still looks like sh*t, because when linearizing
loops sparse doesn't treat the first conditional specially, so instead
of noticing that "0< 10" and getting rid of the first jump, it will
generate the loop with the (general) conditional at the end, which
will then result in lots of phi-nodes etc.
I guess some trivial loop optimizations might be a good idea. But
Kamil's patch looks correct, and the PHI-node cross-bb optimization
does look bogus.
On our point of view, we probably prefer to simply turn off as many
transformations as possible. They just waste time, when an optimizing
LLVM backend is going to perform the same transformations anyway.
Jeff
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