[SelectionDAG] Do minnum->minimum at legalization time instead of building time

The SDAGBuilder behavior stems from the days when we didn't have fast
math flags available in SDAG. We do now and doing the transformation in
the legalizer has the advantage that it also works for vector types.

llvm-svn: 364743

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 33050621348..772ffca1e50 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -5098,6 +5098,17 @@ SDValue TargetLowering::expandFMINNUM_FMAXNUM(SDNode *Node,
     return DAG.getNode(NewOp, dl, VT, Quiet0, Quiet1, Node->getFlags());
   }
 
+  // If the target has FMINIMUM/FMAXIMUM but not FMINNUM/FMAXNUM use that
+  // instead if there are no NaNs.
+  if (Node->getFlags().hasNoNaNs()) {
+    unsigned IEEE2018Op =
+        Node->getOpcode() == ISD::FMINNUM ? ISD::FMINIMUM : ISD::FMAXIMUM;
+    if (isOperationLegalOrCustom(IEEE2018Op, VT)) {
+      return DAG.getNode(IEEE2018Op, dl, VT, Node->getOperand(0),
+                         Node->getOperand(1), Node->getFlags());
+    }
+  }
+
   return SDValue();
 }