Fold fneg and fabs like multiplications

Given no NaNs and no signed zeroes it folds:

(fmul X, (select (fcmp X > 0.0), -1.0, 1.0)) -> (fneg (fabs X))
(fmul X, (select (fcmp X > 0.0), 1.0, -1.0)) -> (fabs X)

Differential Revision: https://reviews.llvm.org/D34579

llvm-svn: 306592

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 88756b7f92e..a8411ffdfb7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9753,6 +9753,52 @@ SDValue DAGCombiner::visitFMUL(SDNode *N) {
     }
   }
 
+  // fold (fmul X, (select (fcmp X > 0.0), -1.0, 1.0)) -> (fneg (fabs X))
+  // fold (fmul X, (select (fcmp X > 0.0), 1.0, -1.0)) -> (fabs X)
+  if (Flags.hasNoNaNs() && Flags.hasNoSignedZeros() &&
+      (N0.getOpcode() == ISD::SELECT || N1.getOpcode() == ISD::SELECT) &&
+      TLI.isOperationLegal(ISD::FABS, VT)) {
+    SDValue Select = N0, X = N1;
+    if (Select.getOpcode() != ISD::SELECT)
+      std::swap(Select, X);
+
+    SDValue Cond = Select.getOperand(0);
+    auto TrueOpnd  = dyn_cast<ConstantFPSDNode>(Select.getOperand(1));
+    auto FalseOpnd = dyn_cast<ConstantFPSDNode>(Select.getOperand(2));
+
+    if (TrueOpnd && FalseOpnd &&
+        Cond.getOpcode() == ISD::SETCC && Cond.getOperand(0) == X &&
+        isa<ConstantFPSDNode>(Cond.getOperand(1)) &&
+        cast<ConstantFPSDNode>(Cond.getOperand(1))->isExactlyValue(0.0)) {
+      ISD::CondCode CC = cast<CondCodeSDNode>(Cond.getOperand(2))->get();
+      switch (CC) {
+      default: break;
+      case ISD::SETOLT:
+      case ISD::SETULT:
+      case ISD::SETOLE:
+      case ISD::SETULE:
+      case ISD::SETLT:
+      case ISD::SETLE:
+        std::swap(TrueOpnd, FalseOpnd);
+        // Fall through
+      case ISD::SETOGT:
+      case ISD::SETUGT:
+      case ISD::SETOGE:
+      case ISD::SETUGE:
+      case ISD::SETGT:
+      case ISD::SETGE:
+        if (TrueOpnd->isExactlyValue(-1.0) && FalseOpnd->isExactlyValue(1.0) &&
+            TLI.isOperationLegal(ISD::FNEG, VT))
+          return DAG.getNode(ISD::FNEG, DL, VT,
+                   DAG.getNode(ISD::FABS, DL, VT, X));
+        if (TrueOpnd->isExactlyValue(1.0) && FalseOpnd->isExactlyValue(-1.0))
+          return DAG.getNode(ISD::FABS, DL, VT, X);
+
+        break;
+      }
+    }
+  }
+
   // FMUL -> FMA combines:
   if (SDValue Fused = visitFMULForFMADistributiveCombine(N)) {
     AddToWorklist(Fused.getNode());