[llvm] 3dc7c5f - [LegalizeTypes] Remove code to create ISD::FP_TO_FP16 from SoftenFloatRes_FTRUNC.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2019-11-25T18:18:40-08:00
New Revision: 3dc7c5f7d83c61fdbce5ad2ab5aad716dd6d1d1e

URL: https://github.com/llvm/llvm-project/commit/3dc7c5f7d83c61fdbce5ad2ab5aad716dd6d1d1e
DIFF: https://github.com/llvm/llvm-project/commit/3dc7c5f7d83c61fdbce5ad2ab5aad716dd6d1d1e.diff

LOG: [LegalizeTypes] Remove code to create ISD::FP_TO_FP16 from SoftenFloatRes_FTRUNC.

There seems to have been a misunderstanding of what ISD::FTRUNC
represents. ISD::FTRUNC is equivalent to llvm.trunc which takes
a floating point value, truncates it without changing the size
of the value and returns it.

Despite its similar name, its different than the fptrunc instruction
in IR which changes a floating point value to a smaller floating
point value. fptrunc is represented by ISD::FP_ROUND in SelectionDAG.

Since the ISD::FP_TO_FP16 node takes a floating point value and
converts it to f16 its more similar to ISD::FP_ROUND. In fact there
is identical code to what is being removed here in SoftenFloatRes_FP_ROUND.

I assume this bug was never encountered because it would require
f16 to be legalized by softening rather than the default of
promoting.

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
index af963bc02802..c4a74d5c1c71 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp
@@ -705,9 +705,6 @@ SDValue DAGTypeLegalizer::SoftenFloatRes_FSUB(SDNode *N) {
 
 SDValue DAGTypeLegalizer::SoftenFloatRes_FTRUNC(SDNode *N) {
   EVT NVT = TLI.getTypeToTransformTo(*DAG.getContext(), N->getValueType(0));
-  if (N->getValueType(0) == MVT::f16)
-    return DAG.getNode(ISD::FP_TO_FP16, SDLoc(N), NVT, N->getOperand(0));
-
   SDValue Op = GetSoftenedFloat(N->getOperand(0));
   TargetLowering::MakeLibCallOptions CallOptions;
   EVT OpsVT[1] = { N->getOperand(0).getValueType() };