[llvm] r235508 - Fixed logic to enable complex FMA formation.

[Olivier Sallenave]

Hi Eric,

The change ensures that if (HasFMAD && LookThroughFPExt && !UnsafeFPMath)
we do not perform transforms that alter the precision. To my knowledge
there is no target for which (HasFMAD && LookThroughFPExt) would be true --
this is a change for potential future targets. Is it fine not to have a
testcase then?

Thanks,

Olivier

2015-04-22 10:20 GMT-04:00 Eric Christopher <echristo at gmail.com>:

> Test case? Also while it's fairly obvious what you did if you look at the
> code a more verbose commit message is often helpful. Thanks!
>
> -eric
>
> On Wed, Apr 22, 2015, 7:13 AM Olivier Sallenave <ohsallen at us.ibm.com>
> wrote:
>
>> Author: ohsallen
>> Date: Wed Apr 22 09:07:26 2015
>> New Revision: 235508
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=235508&view=rev
>> Log:
>> Fixed logic to enable complex FMA formation.
>>
>> Modified:
>>     llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>>
>> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=235508&r1=235507&r2=235508&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
>> +++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Wed Apr 22
>> 09:07:26 2015
>> @@ -7164,7 +7164,7 @@ SDValue DAGCombiner::visitFADDForFMAComb
>>                                       N0));
>>      }
>>
>> -    if (LookThroughFPExt) {
>> +    if (UnsafeFPMath && LookThroughFPExt) {
>>        // fold (fadd (fma x, y, (fpext (fmul u, v))), z)
>>        //   -> (fma x, y, (fma (fpext u), (fpext v), z))
>>        auto FoldFAddFMAFPExtFMul = [&] (
>> @@ -7415,7 +7415,7 @@ SDValue DAGCombiner::visitFSUBForFMAComb
>>                                       N21, N0));
>>      }
>>
>> -    if (LookThroughFPExt) {
>> +    if (UnsafeFPMath && LookThroughFPExt) {
>>        // fold (fsub (fma x, y, (fpext (fmul u, v))), z)
>>        //   -> (fma x, y (fma (fpext u), (fpext v), (fneg z)))
>>        if (N0.getOpcode() == PreferredFusedOpcode) {
>>
>>
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