[RFBT] Fix PR middle-end/37263, extra code for doloop with unsigned 32bit types on LP64

[Bernd Schmidt]

Andrew Pinski wrote:

>   The issue here is that in 4.1 and 4.0, IV-opts used to replace a < b
> with a != b which causes doloop not to create extra branches as it
> knows that the iterations are already correct.  Since
> http://www.nabble.com/-patch--Fix-nonsensical-exit-test-replacement-td8289646.html,
> IV-opts no longer does this as it thinks it is not profitable to do
> it.  Well the issue is that the cost are the same.  We should prefer
> the replacement version if the cost is the same as it allows the RTL
> optimizers to do better job; though another solution would be
> propagate that information down to RTL level from the tree level but
> that is not suitable for stage 3 really

I've tried the patch in a 4.3-based Blackfin compiler, and it generates 
a lot more hardware loops.

> * tree-ssa-loop-ivopts.c (determine_use_iv_cost_condition): Prefer the
> eliminate IV if the cost are the same.

Ok.  Thanks!


Bernd
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