[RISCV] Don't promote f16 FNEG/FABS with Zfhmin/Zhinxmin. (llvm#106474)

fneg/fabs are not supposed to canonicalize nans. Promoting to f32 will
go through an fp_extend which will canonicalize. The generic Promote
handler needs to be removed from LegalizeDAG.

We need to use integer bit manip to clear the bit instead.

Unfortunately, this is going through the stack due to i16 not being a
legal type. Fixing that will require custom legalization or some other
generic SelectionDAG change.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -395,7 +395,6 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
       ISD::FADD,          ISD::FSUB,
       ISD::FMUL,          ISD::FMA,
       ISD::FDIV,          ISD::FSQRT,
-      ISD::FABS,          ISD::FNEG,
       ISD::STRICT_FMA,    ISD::STRICT_FADD,
       ISD::STRICT_FSUB,   ISD::STRICT_FMUL,
       ISD::STRICT_FDIV,   ISD::STRICT_FSQRT,
@@ -416,8 +415,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::BR_CC, MVT::bf16, Expand);
     setOperationAction(ZfhminZfbfminPromoteOps, MVT::bf16, Promote);
     setOperationAction(ISD::FREM, MVT::bf16, Promote);
-    // FIXME: Need to promote bf16 FCOPYSIGN to f32, but the
-    // DAGCombiner::visitFP_ROUND probably needs improvements first.
+    setOperationAction(ISD::FABS, MVT::bf16, Expand);
+    setOperationAction(ISD::FNEG, MVT::bf16, Expand);
     setOperationAction(ISD::FCOPYSIGN, MVT::bf16, Expand);
   }
 
@@ -433,8 +432,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
       setOperationAction({ISD::STRICT_LRINT, ISD::STRICT_LLRINT,
                           ISD::STRICT_LROUND, ISD::STRICT_LLROUND},
                          MVT::f16, Legal);
-      // FIXME: Need to promote f16 FCOPYSIGN to f32, but the
-      // DAGCombiner::visitFP_ROUND probably needs improvements first.
+      setOperationAction(ISD::FABS, MVT::f16, Expand);
+      setOperationAction(ISD::FNEG, MVT::f16, Expand);
       setOperationAction(ISD::FCOPYSIGN, MVT::f16, Expand);
     }