[X86] Suppress load folding into and/or/xor if it will prevent matching btr/bts/btc.

This is a follow up to r335753. At the time I forgot about isProfitableToFold which makes this pretty easy.

Differential Revision: https://reviews.llvm.org/D48706

llvm-svn: 335895

1 files changed, 29 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index e54115e532a..c7120cf3673 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -569,6 +569,35 @@ X86DAGToDAGISel::IsProfitableToFold(SDValue N, SDNode *U, SDNode *Root) const {
           return false;
       }
 
+      // Don't fold load if this matches the BTS/BTR/BTC patterns.
+      // BTS: (or X, (shl 1, n))
+      // BTR: (and X, (rotl -2, n))
+      // BTC: (xor X, (shl 1, n))
+      if (U->getOpcode() == ISD::OR || U->getOpcode() == ISD::XOR) {
+        if (U->getOperand(0).getOpcode() == ISD::SHL &&
+            isOneConstant(U->getOperand(0).getOperand(0)))
+          return false;
+
+        if (U->getOperand(1).getOpcode() == ISD::SHL &&
+            isOneConstant(U->getOperand(1).getOperand(0)))
+          return false;
+      }
+      if (U->getOpcode() == ISD::AND) {
+        SDValue U0 = U->getOperand(0);
+        SDValue U1 = U->getOperand(1);
+        if (U0.getOpcode() == ISD::ROTL) {
+          auto *C = dyn_cast<ConstantSDNode>(U0.getOperand(0));
+          if (C && C->getSExtValue() == -2)
+            return false;
+        }
+
+        if (U1.getOpcode() == ISD::ROTL) {
+          auto *C = dyn_cast<ConstantSDNode>(U1.getOperand(0));
+          if (C && C->getSExtValue() == -2)
+            return false;
+        }
+      }
+
       break;
     }
     case ISD::SHL: