diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -1090,7 +1090,6 @@
 void MachineInstr::tieOperands(unsigned DefIdx, unsigned UseIdx) {
   MachineOperand &DefMO = getOperand(DefIdx);
   MachineOperand &UseMO = getOperand(UseIdx);
-  assert(DefMO.isDef() && "DefIdx must be a def operand");
   assert(UseMO.isUse() && "UseIdx must be a use operand");
   assert(!DefMO.isTied() && "Def is already tied to another use");
   assert(!UseMO.isTied() && "Use is already tied to another def");
diff --git a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
--- a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -1324,6 +1324,10 @@
     // Tied constraint already satisfied?
     if (SrcReg == DstReg)
       continue;
+    // Ignore tied operands where both are source operands.
+    if (!DstMO.isDef()) {
+      continue;
+    }
 
     assert(SrcReg && SrcMO.isUse() && "two address instruction invalid");
 
diff --git a/llvm/test/TableGen/ConstraintChecking4.td b/llvm/test/TableGen/ConstraintChecking4.td
--- a/llvm/test/TableGen/ConstraintChecking4.td
+++ b/llvm/test/TableGen/ConstraintChecking4.td
@@ -2,5 +2,5 @@
 
 include "ConstraintChecking.inc"
 
-// CHECK: [[FILE]]:[[@LINE+1]]:1: error: Output operands '$dest1' and '$dest2' of 'Foo' cannot be tied!
-def Foo : TestInstructionWithConstraints<"$dest1 = $dest2">;
+// CHECK: [[FILE]]:[[@LINE+1]]:1: error: Operand '$dest1' of 'Foo' cannot have multiple operands tied to it!
+def Foo : TestInstructionWithConstraints<"$dest1 = $src1, $dest1 = $src2">;
diff --git a/llvm/test/TableGen/ConstraintChecking5.td b/llvm/test/TableGen/ConstraintChecking5.td
--- a/llvm/test/TableGen/ConstraintChecking5.td
+++ b/llvm/test/TableGen/ConstraintChecking5.td
@@ -2,5 +2,5 @@
 
 include "ConstraintChecking.inc"
 
-// CHECK: [[FILE]]:[[@LINE+1]]:1: error: Input operands '$src1' and '$src2' of 'Foo' cannot be tied!
-def Foo : TestInstructionWithConstraints<"$src1 = $src2">;
+// CHECK: [[FILE]]:[[@LINE+1]]:1: error: Operand '$src1' of 'Foo' cannot have multiple constraints!
+def Foo : TestInstructionWithConstraints<"$dest1 = $src1, $dest2 = $src1">;
diff --git a/llvm/test/TableGen/ConstraintChecking6.td b/llvm/test/TableGen/ConstraintChecking6.td
deleted file mode 100644
--- a/llvm/test/TableGen/ConstraintChecking6.td
+++ /dev/null
@@ -1,6 +0,0 @@
-// RUN: not llvm-tblgen -gen-asm-writer -I %p -I %p/../../include %s 2>&1 | FileCheck %s -DFILE=%s
-
-include "ConstraintChecking.inc"
-
-// CHECK: [[FILE]]:[[@LINE+1]]:1: error: Operand '$dest1' of 'Foo' cannot have multiple operands tied to it!
-def Foo : TestInstructionWithConstraints<"$dest1 = $src1, $dest1 = $src2">;
diff --git a/llvm/test/TableGen/ConstraintChecking7.td b/llvm/test/TableGen/ConstraintChecking7.td
deleted file mode 100644
--- a/llvm/test/TableGen/ConstraintChecking7.td
+++ /dev/null
@@ -1,6 +0,0 @@
-// RUN: not llvm-tblgen -gen-asm-writer -I %p -I %p/../../include %s 2>&1 | FileCheck %s -DFILE=%s
-
-include "ConstraintChecking.inc"
-
-// CHECK: [[FILE]]:[[@LINE+1]]:1: error: Operand '$src1' of 'Foo' cannot have multiple constraints!
-def Foo : TestInstructionWithConstraints<"$dest1 = $src1, $dest2 = $src1">;
diff --git a/llvm/utils/TableGen/CodeGenInstruction.cpp b/llvm/utils/TableGen/CodeGenInstruction.cpp
--- a/llvm/utils/TableGen/CodeGenInstruction.cpp
+++ b/llvm/utils/TableGen/CodeGenInstruction.cpp
@@ -291,16 +291,6 @@
   std::pair<unsigned,unsigned> SrcOp = (FirstIsDest ? RHSOp : LHSOp);
   StringRef SrcOpName = (FirstIsDest ? RHSOpName : LHSOpName);
 
-  // Ensure one operand is a def and the other is a use.
-  if (DestOp.first >= Ops.NumDefs)
-    PrintFatalError(
-      Rec->getLoc(), "Input operands '" + LHSOpName + "' and '" + RHSOpName +
-      "' of '" + Rec->getName() + "' cannot be tied!");
-  if (SrcOp.first < Ops.NumDefs)
-    PrintFatalError(
-      Rec->getLoc(), "Output operands '" + LHSOpName + "' and '" + RHSOpName +
-      "' of '" + Rec->getName() + "' cannot be tied!");
-
   // The constraint has to go on the operand with higher index, i.e.
   // the source one. Check there isn't another constraint there
   // already.