[PATCH] D80974: [DAGCombine] Adding a hook to improve the precision of fsqrt if the input is denormal

[ChenZheng via Phabricator via llvm-commits]

shchenz accepted this revision.
shchenz added inline comments.
This revision is now accepted and ready to land.


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Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:21981
+            Test.getValueType().isVector() ? ISD::VSELECT : ISD::SELECT, DL, VT,
+            Test, TLI.getSqrtResultForDenormInput(Op, DAG), Est);
       }
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On Powerpc target, we use 0.0 as denormal float point sqrt result for a long time. Changing the result to hardware sqrt instructions will improve the precision for sure, but it also degrades the runtime performance. Is it possible to do it like: if we concern about performance, we use 0.0, if we concern about precision, we use hardware sqrt instruction. Maybe `-Ofast` is an indicatation for this?


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https://reviews.llvm.org/D80974