[llvm-commits] [llvm] r108639 - /llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
Dale Johannesen
dalej at apple.com
Mon Jul 19 10:56:21 PDT 2010
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.
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