[AArch64] Only fold into ands directly if AND is one-use

Otherwise, we can be too aggressive, and when it comes time to split along edges, we can end up duplicating more than we bargained for.

Author: AZero13

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -3745,19 +3745,13 @@ static SDValue emitComparison(SDValue LHS, SDValue RHS, ISD::CondCode CC,
     Opcode = AArch64ISD::ADDS;
     LHS = LHS.getOperand(1);
   } else if (isNullConstant(RHS) && !isUnsignedIntSetCC(CC)) {
-    if (LHS.getOpcode() == ISD::AND) {
+    if (LHS.getOpcode() == ISD::AND && LHS.hasOneUse()) {
       // Similarly, (CMP (and X, Y), 0) can be implemented with a TST
-      // (a.k.a. ANDS) except that the flags are only guaranteed to work for one
-      // of the signed comparisons.
-      const SDValue ANDSNode =
-          DAG.getNode(AArch64ISD::ANDS, DL, DAG.getVTList(VT, FlagsVT),
-                      LHS.getOperand(0), LHS.getOperand(1));
-      // Replace all users of (and X, Y) with newly generated (ands X, Y)
-      DAG.ReplaceAllUsesWith(LHS, ANDSNode);
-      return ANDSNode.getValue(1);
-    } else if (LHS.getOpcode() == AArch64ISD::ANDS) {
-      // Use result of ANDS
-      return LHS.getValue(1);
+      // (a.k.a. ANDS) except that the flags are only guaranteed to work for
+      // signed comparisons.
+      Opcode = AArch64ISD::ANDS;
+      RHS = LHS.getOperand(1);
+      LHS = LHS.getOperand(0);
     }
   }
 

llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp

@@ -5109,14 +5109,14 @@ MachineInstr *AArch64InstructionSelector::tryFoldIntegerCompare(
   //
   // tst x, y
   if (!CmpInst::isUnsigned(P) && LHSDef &&
-      LHSDef->getOpcode() == TargetOpcode::G_AND) {
+      LHSDef->getOpcode() == TargetOpcode::G_AND &&
+      MRI.hasOneNonDBGUse(LHS.getReg())) {
     // Make sure that the RHS is 0.
     auto ValAndVReg = getIConstantVRegValWithLookThrough(RHS.getReg(), MRI);
     if (!ValAndVReg || ValAndVReg->Value != 0)
       return nullptr;
 
-    return emitTST(LHSDef->getOperand(1),
-                   LHSDef->getOperand(2), MIRBuilder);
+    return emitTST(LHSDef->getOperand(1), LHSDef->getOperand(2), MIRBuilder);
   }
 
   return nullptr;