[llvm-commits] [llvm-gcc-4.2] r82640 - /llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp

[Dale Johannesen]

On Sep 23, 2009, at 3:18 PMPDT, Evan Cheng wrote:

> Are we generating a call to sqrt now? If so, that's bad. We should  
> be using SSE sqrts* instructions.

Agreed.  My proposed semantic change would fix that.

> Evan
>
> On Sep 23, 2009, at 3:12 PM, Evan Cheng wrote:
>
>>
>> On Sep 23, 2009, at 2:18 PM, Dale Johannesen wrote:
>>
>>> While this is certainly necessary given the current IR definition,  
>>> I'm
>>> not too happy about it, as we will lose something because the
>>> optimizers must consider that sqrt might set errno.  What I'd like  
>>> to
>>> do is redefine llvm.sqrt in the IR to mean "same behavior as sqrt
>>> except that it doesn't set errno", and likewise for llvm.pow,  
>>> etc.  It
>>> looks like that was the original intent, actually, but that's not  
>>> what
>>> it says.  Any objections?
>>
>> Are we doing any optimizations on llvm.sqrt?
>>
>> Evan
>>
>>>
>>> On Sep 23, 2009, at 11:50 AMPDT, Dale Johannesen wrote:
>>>
>>>> Author: johannes
>>>> Date: Wed Sep 23 13:50:32 2009
>>>> New Revision: 82640
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=82640&view=rev
>>>> Log:
>>>> The result of sqrt(negative) is implementation-defined, but follows
>>>> IEEE754 in most current implementations. llvm.sqrt, which has
>>>> undefined
>>>> behavior for such inputs, is an inappropriate substitute which can
>>>> change
>>>> the result.
>>>
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