[llvm-commits] [llvm] r64918 - in /llvm/trunk: include/llvm/Analysis/ScalarEvolution.h lib/Analysis/ScalarEvolution.cpp lib/Transforms/Scalar/IndVarSimplify.cpp test/Transforms/IndVarSimplify/preserve-signed-wrap.ll test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll test/Transforms/IndVarSimplify/signed-trip-count.ll

[Dan Gohman]

On Feb 23, 2009, at 2:30 PM, Chris Lattner wrote:

>
> On Feb 19, 2009, at 11:35 AM, Dan Gohman wrote:
>
>>
>> On Feb 18, 2009, at 10:07 AM, Chris Lattner wrote:
>>
>>>
>>> On Feb 18, 2009, at 9:22 AM, Dan Gohman wrote:
>>>
>>>> Author: djg
>>>> Date: Wed Feb 18 11:22:41 2009
>>>> New Revision: 64918
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=64918&view=rev
>>>> Log:
>>>> Use a sign-extend instead of a zero-extend when promoting a
>>>> trip count value when the original loop iteration condition is
>>>> signed and the canonical induction variable won't undergo signed
>>>> overflow. This isn't required for correctness; it just preserves
>>>> more information about original loop iteration values.
>>>
>>> Dan, I'm concerned about this.  Sign extensions are generally more
>>> expensive than zero extensions, and much of the optimizer
>>> canonicalizes sign extends to zero extends.
>>
>>
>> You're right. I'm reconsidering this; It may not actually
>> be needed.
>
> Should the patch be reverted?

Yes. I've now done so.

Dan