diff --git a/llvm/lib/Analysis/ConstraintSystem.cpp b/llvm/lib/Analysis/ConstraintSystem.cpp
index 633427ee6c5b1e..fd96c61e9a94ce 100644
--- a/llvm/lib/Analysis/ConstraintSystem.cpp
+++ b/llvm/lib/Analysis/ConstraintSystem.cpp
@@ -28,32 +28,39 @@ bool ConstraintSystem::eliminateUsingFM() {
   assert(!Constraints.empty() &&
          "should only be called for non-empty constraint systems");
   unsigned NumVariables = Constraints[0].size();
-  SmallVector<SmallVector<int64_t, 8>, 4> NewSystem;
 
-  unsigned NumConstraints = Constraints.size();
   uint32_t NewGCD = 1;
   unsigned LastIdx = NumVariables - 1;
 
-  for (unsigned R1 = 0; R1 < NumConstraints; R1++) {
+  // First, either remove the variable in place if it is 0 or add the row to
+  // RemainingRows and remove it from the system.
+  SmallVector<SmallVector<int64_t, 8>, 4> RemainingRows;
+  for (unsigned R1 = 0; R1 < Constraints.size();) {
     SmallVector<int64_t, 8> &Row1 = Constraints[R1];
     int64_t LowerLast = Row1[LastIdx];
     if (LowerLast == 0) {
       Row1.pop_back();
-      NewSystem.push_back(std::move(Row1));
-      continue;
+      R1++;
+    } else {
+      std::swap(Constraints[R1], Constraints.back());
+      RemainingRows.push_back(std::move(Constraints.back()));
+      Constraints.pop_back();
     }
+  }
 
+  // Process rows where the variable is != 0.
+  unsigned NumRemainingConstraints = RemainingRows.size();
+  for (unsigned R1 = 0; R1 < NumRemainingConstraints; R1++) {
     // FIXME do not use copy
-    for (unsigned R2 = R1 + 1; R2 < NumConstraints; R2++) {
+    for (unsigned R2 = R1 + 1; R2 < NumRemainingConstraints; R2++) {
       if (R1 == R2)
         continue;
 
-      int64_t UpperLast = Constraints[R2][LastIdx];
-      // FIXME: can we do better than just dropping things here?
-      if (UpperLast == 0)
-        continue;
-
-      int64_t LowerLast = Constraints[R1][LastIdx];
+      int64_t UpperLast = RemainingRows[R2][LastIdx];
+      int64_t LowerLast = RemainingRows[R1][LastIdx];
+      assert(
+          UpperLast != 0 && LowerLast != 0 &&
+          "RemainingRows should only contain rows where the variable is != 0");
       if ((LowerLast < 0 && UpperLast < 0) || (LowerLast > 0 && UpperLast > 0))
         continue;
 
@@ -67,10 +74,10 @@ bool ConstraintSystem::eliminateUsingFM() {
       SmallVector<int64_t, 8> NR;
       for (unsigned I = 0; I < LastIdx; I++) {
         int64_t M1, M2, N;
-        int64_t UpperV = Constraints[UpperR][I];
+        int64_t UpperV = RemainingRows[UpperR][I];
         if (MulOverflow(UpperV, ((-1) * LowerLast / GCD), M1))
           return false;
-        int64_t LowerV = Constraints[LowerR][I];
+        int64_t LowerV = RemainingRows[LowerR][I];
         if (MulOverflow(LowerV, (UpperLast / GCD), M2))
           return false;
         if (AddOverflow(M1, M2, N))
@@ -81,13 +88,12 @@ bool ConstraintSystem::eliminateUsingFM() {
             APIntOps::GreatestCommonDivisor({32, (uint32_t)N}, {32, NewGCD})
                 .getZExtValue();
       }
-      NewSystem.push_back(std::move(NR));
+      Constraints.push_back(std::move(NR));
       // Give up if the new system gets too big.
-      if (NewSystem.size() > 500)
+      if (Constraints.size() > 500)
         return false;
     }
   }
-  Constraints = std::move(NewSystem);
   GCD = NewGCD;
 
   return true;