[llvm] r330947 - [DAGCombiner] refactor FP->int->FP folds; NFC

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Thu Apr 26 08:20:18 2018
New Revision: 330947

URL: http://llvm.org/viewvc/llvm-project?rev=330947&view=rev
Log:
[DAGCombiner] refactor FP->int->FP folds; NFC

As discussed in the post-review comments for rL330437,
we need to guard this fold to allow existing code to
keep working with the undefined behavior that they've
come to rely on.

That would mean duplicating more code than we already 
have, so let's fix that first. 

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=330947&r1=330946&r2=330947&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Thu Apr 26 08:20:18 2018
@@ -10902,6 +10902,28 @@ SDValue DAGCombiner::visitFCOPYSIGN(SDNo
   return SDValue();
 }
 
+static SDValue foldFPToIntToFP(SDNode *N, SelectionDAG &DAG,
+                               const TargetLowering &TLI) {
+  // We only do this if the target has legal ftrunc. Otherwise, we'd likely be
+  // replacing casts with a libcall.
+  EVT VT = N->getValueType(0);
+  if (!TLI.isOperationLegal(ISD::FTRUNC, VT))
+    return SDValue();
+
+  // fptosi/fptoui round towards zero, so converting from FP to integer and
+  // back is the same as an 'ftrunc': [us]itofp (fpto[us]i X) --> ftrunc X
+  SDValue N0 = N->getOperand(0);
+  if (N->getOpcode() == ISD::SINT_TO_FP && N0.getOpcode() == ISD::FP_TO_SINT &&
+      N0.getOperand(0).getValueType() == VT)
+    return DAG.getNode(ISD::FTRUNC, SDLoc(N), VT, N0.getOperand(0));
+
+  if (N->getOpcode() == ISD::UINT_TO_FP && N0.getOpcode() == ISD::FP_TO_UINT &&
+      N0.getOperand(0).getValueType() == VT)
+    return DAG.getNode(ISD::FTRUNC, SDLoc(N), VT, N0.getOperand(0));
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitSINT_TO_FP(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   EVT VT = N->getValueType(0);
@@ -10953,14 +10975,8 @@ SDValue DAGCombiner::visitSINT_TO_FP(SDN
     }
   }
 
-  // fptosi rounds towards zero, so converting from FP to integer and back is
-  // the same as an 'ftrunc': sitofp (fptosi X) --> ftrunc X
-  // We only do this if the target has legal ftrunc, otherwise we'd likely be
-  // replacing casts with a libcall.
-  if (N0.getOpcode() == ISD::FP_TO_SINT &&
-      N0.getOperand(0).getValueType() == VT &&
-      TLI.isOperationLegal(ISD::FTRUNC, VT))
-    return DAG.getNode(ISD::FTRUNC, SDLoc(N), VT, N0.getOperand(0));
+  if (SDValue FTrunc = foldFPToIntToFP(N, DAG, TLI))
+    return FTrunc;
 
   return SDValue();
 }
@@ -11001,14 +11017,8 @@ SDValue DAGCombiner::visitUINT_TO_FP(SDN
     }
   }
 
-  // fptoui rounds towards zero, so converting from FP to integer and back is
-  // the same as an 'ftrunc': uitofp (fptoui X) --> ftrunc X
-  // We only do this if the target has legal ftrunc, otherwise we'd likely be
-  // replacing casts with a libcall.
-  if (N0.getOpcode() == ISD::FP_TO_UINT &&
-      N0.getOperand(0).getValueType() == VT &&
-      TLI.isOperationLegal(ISD::FTRUNC, VT))
-    return DAG.getNode(ISD::FTRUNC, SDLoc(N), VT, N0.getOperand(0));
+  if (SDValue FTrunc = foldFPToIntToFP(N, DAG, TLI))
+    return FTrunc;
 
   return SDValue();
 }