diff --git a/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp b/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
--- a/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
+++ b/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
@@ -431,8 +431,10 @@
   bool reuniteExts(Instruction *I);
 
   /// Find the closest dominator of <Dominatee> that is equivalent to <Key>.
-  Instruction *findClosestMatchingDominator(const SCEV *Key,
-                                            Instruction *Dominatee);
+  Instruction *findClosestMatchingDominator(
+      const SCEV *Key, Instruction *Dominatee,
+      DenseMap<const SCEV *, SmallVector<Instruction *, 2>> &DominatingExprs);
+
   /// Verify F is free of dead code.
   void verifyNoDeadCode(Function &F);
 
@@ -456,7 +458,8 @@
   /// multiple GEPs with a single index.
   bool LowerGEP;
 
-  DenseMap<const SCEV *, SmallVector<Instruction *, 2>> DominatingExprs;
+  DenseMap<const SCEV *, SmallVector<Instruction *, 2>> DominatingAdds;
+  DenseMap<const SCEV *, SmallVector<Instruction *, 2>> DominatingSubs;
 };
 
 } // end anonymous namespace
@@ -1141,7 +1144,8 @@
 }
 
 Instruction *SeparateConstOffsetFromGEP::findClosestMatchingDominator(
-    const SCEV *Key, Instruction *Dominatee) {
+    const SCEV *Key, Instruction *Dominatee,
+    DenseMap<const SCEV *, SmallVector<Instruction *, 2>> &DominatingExprs) {
   auto Pos = DominatingExprs.find(Key);
   if (Pos == DominatingExprs.end())
     return nullptr;
@@ -1169,12 +1173,23 @@
   // If Dom can't sign overflow and Dom dominates I, optimize I to sext(Dom).
   // TODO: handle zext
   Value *LHS = nullptr, *RHS = nullptr;
-  if (match(I, m_Add(m_SExt(m_Value(LHS)), m_SExt(m_Value(RHS)))) ||
-      match(I, m_Sub(m_SExt(m_Value(LHS)), m_SExt(m_Value(RHS))))) {
+  if (match(I, m_Add(m_SExt(m_Value(LHS)), m_SExt(m_Value(RHS))))) {
     if (LHS->getType() == RHS->getType()) {
       const SCEV *Key =
           SE->getAddExpr(SE->getUnknown(LHS), SE->getUnknown(RHS));
-      if (auto *Dom = findClosestMatchingDominator(Key, I)) {
+      if (auto *Dom = findClosestMatchingDominator(Key, I, DominatingAdds)) {
+        Instruction *NewSExt = new SExtInst(Dom, I->getType(), "", I);
+        NewSExt->takeName(I);
+        I->replaceAllUsesWith(NewSExt);
+        RecursivelyDeleteTriviallyDeadInstructions(I);
+        return true;
+      }
+    }
+  } else if (match(I, m_Sub(m_SExt(m_Value(LHS)), m_SExt(m_Value(RHS))))) {
+    if (LHS->getType() == RHS->getType()) {
+      const SCEV *Key =
+          SE->getAddExpr(SE->getUnknown(LHS), SE->getUnknown(RHS));
+      if (auto *Dom = findClosestMatchingDominator(Key, I, DominatingSubs)) {
         Instruction *NewSExt = new SExtInst(Dom, I->getType(), "", I);
         NewSExt->takeName(I);
         I->replaceAllUsesWith(NewSExt);
@@ -1185,12 +1200,17 @@
   }
 
   // Add I to DominatingExprs if it's an add/sub that can't sign overflow.
-  if (match(I, m_NSWAdd(m_Value(LHS), m_Value(RHS))) ||
-      match(I, m_NSWSub(m_Value(LHS), m_Value(RHS)))) {
+  if (match(I, m_NSWAdd(m_Value(LHS), m_Value(RHS)))) {
+    if (programUndefinedIfFullPoison(I)) {
+      const SCEV *Key =
+          SE->getAddExpr(SE->getUnknown(LHS), SE->getUnknown(RHS));
+      DominatingAdds[Key].push_back(I);
+    }
+  } else if (match(I, m_NSWSub(m_Value(LHS), m_Value(RHS)))) {
     if (programUndefinedIfFullPoison(I)) {
       const SCEV *Key =
           SE->getAddExpr(SE->getUnknown(LHS), SE->getUnknown(RHS));
-      DominatingExprs[Key].push_back(I);
+      DominatingSubs[Key].push_back(I);
     }
   }
   return false;
@@ -1198,7 +1218,8 @@
 
 bool SeparateConstOffsetFromGEP::reuniteExts(Function &F) {
   bool Changed = false;
-  DominatingExprs.clear();
+  DominatingAdds.clear();
+  DominatingSubs.clear();
   for (const auto Node : depth_first(DT)) {
     BasicBlock *BB = Node->getBlock();
     for (auto I = BB->begin(); I != BB->end(); ) {
diff --git a/llvm/test/Transforms/SeparateConstOffsetFromGEP/test-add-sub-separation.ll b/llvm/test/Transforms/SeparateConstOffsetFromGEP/test-add-sub-separation.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/SeparateConstOffsetFromGEP/test-add-sub-separation.ll
@@ -0,0 +1,31 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -separate-const-offset-from-gep < %s | FileCheck %s
+
+define void @matchingExtensions(i32* %ap, i32* %bp, i64* %result) {
+; CHECK-LABEL: @matchingExtensions(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[A:%.*]] = load i32, i32* [[AP:%.*]]
+; CHECK-NEXT:    [[B:%.*]] = load i32, i32* [[BP:%.*]]
+; CHECK-NEXT:    [[EB:%.*]] = sext i32 [[B]] to i64
+; CHECK-NEXT:    [[SUBAB:%.*]] = sub nsw i32 [[A]], [[B]]
+; CHECK-NEXT:    [[EA:%.*]] = sext i32 [[A]] to i64
+; CHECK-NEXT:    [[ADDEAEB:%.*]] = add nsw i64 [[EA]], [[EB]]
+; CHECK-NEXT:    [[EXTSUB:%.*]] = sext i32 [[SUBAB]] to i64
+; CHECK-NEXT:    [[IDX:%.*]] = getelementptr i32, i32* [[AP]], i64 [[EXTSUB]]
+; CHECK-NEXT:    store i64 [[ADDEAEB]], i64* [[RESULT:%.*]]
+; CHECK-NEXT:    store i32 [[SUBAB]], i32* [[IDX]]
+; CHECK-NEXT:    ret void
+;
+entry:
+  %a = load i32, i32* %ap
+  %b = load i32, i32* %bp
+  %eb = sext i32 %b to i64
+  %subab = sub nsw i32 %a, %b
+  %ea = sext i32 %a to i64
+  %addeaeb = add nsw i64 %ea, %eb
+  %extsub = sext i32 %subab to i64
+  %idx = getelementptr i32, i32* %ap, i64 %extsub
+  store i64 %addeaeb, i64* %result
+  store i32 %subab, i32* %idx
+  ret void
+}