[llvm] [LoongArch] Pass 'half' in the lower 16 bits of an f32 value when F extension is enabled (PR #109368)

[Matt Arsenault via llvm-commits]

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@@ -1354,6 +1358,40 @@ SDValue LoongArchTargetLowering::lowerVECTOR_SHUFFLE(SDValue Op,
   return SDValue();
 }
 
+SDValue LoongArchTargetLowering::lowerFP_TO_FP16(SDValue Op,
+                                                 SelectionDAG &DAG) const {
+  // Custom lower to ensure the libcall return is passed in an FPR on hard
+  // float ABIs.
+  SDLoc DL(Op);
+  MakeLibCallOptions CallOptions;
+  SDValue Op0 = Op.getOperand(0);
+  SDValue Chain = SDValue();
+  RTLIB::Libcall LC = RTLIB::getFPROUND(Op0.getValueType(), MVT::f16);
+  SDValue Res;
+  std::tie(Res, Chain) =
+      makeLibCall(DAG, LC, MVT::f32, Op0, CallOptions, DL, Chain);
+  if (Subtarget.is64Bit())
+    return DAG.getNode(LoongArchISD::MOVFR2GR_S_LA64, DL, MVT::i64, Res);
+  return DAG.getBitcast(MVT::i32, Res);
+}
+
+SDValue LoongArchTargetLowering::lowerFP16_TO_FP(SDValue Op,
+                                                 SelectionDAG &DAG) const {
+  // Custom lower to ensure the libcall argument is passed in an FPR on hard
+  // float ABIs.
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arsenm wrote:

You shouldn't need to custom lower the casts to change the ABI. Are you trying to special case the ABI for this one call in this one instance? That seems bad 

https://github.com/llvm/llvm-project/pull/109368