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Re: [PATCH] Add zero-overhead looping for xtensa backend


On Thu, Oct 23, 2014 at 9:12 PM, Yangfei (Felix) <felix.yang@huawei.com> wrote:
>> Here the key point is we need a general purpose register for the "loop"
>> instruction.

So the question to ask here is, "How does this work today, without
loop instructions?" Somehow--even when it has been spilled--a branch
instruction can test the trip count. There should be no difference.

>> And we cannot use zero-cost looping in this situation.
>> And that's why I spilt the zero_cost_loop_end into a normal test and branch.

> Also note that the hwloop_pattern_reg interface also expects a general purpose register in the doloop_end pattern.

If there were no loop instruction, how would this work?


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