[llvm-commits] [llvm] r108639 - /llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

[Dale Johannesen]

On Jul 18, 2010, at 1:12 PMPDT, Chris Lattner wrote:

> On Jul 18, 2010, at 1:02 PM, Owen Anderson wrote:
> On Jul 18, 2010, at 12:52 PM, Chris Lattner wrote:
>>>
>>> I would prefer for this to happen in InstCombiner::visitFPTrunc.   
>>> Both because we already have the infrastructure to do this there,  
>>> but also because your code only handles the -fno-math-errno case.   
>>> Normal calls to libm sqrt should be transformed, not just llvm.sqrt.
>>
>> Do we really want InstCombine assigning semantic value to random  
>> functions named sqrt()?  I understand SimplifyLibCalls doing this,  
>> since it implicitly assumes that we're using libc, but I'm wary of  
>> making InstCombine assume it.
>
> Yes we do.  When/if we support -fno-builtin-sqrt, we will do this by  
> adding a "not a builtin" function attribute, which optimizations  
> like this should listen to.

This is adding the assumption that the source language is C-based, or  
otherwise has a sqrt (as Fortran).  So far this assumption has been  
quarantined in SimplifyLibCalls.