diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1941,6 +1941,32 @@
 
     return false;
   }
+
+  /// Eliminates writes to locations where the value that is being written
+  /// is already stored at the same location.
+  bool eliminateRedundantStoresOfExistingValues() {
+    bool MadeChange = false;
+    LLVM_DEBUG(dbgs() << "Trying to eliminate MemoryDefs that write the "
+                         "already existing value\n");
+    for (auto *Def : MemDefs) {
+      if (SkipStores.contains(Def) || MSSA.isLiveOnEntryDef(Def) ||
+          !isRemovable(Def->getMemoryInst()))
+        continue;
+      auto *UpperDef = dyn_cast<MemoryDef>(Def->getDefiningAccess());
+      if (!UpperDef || MSSA.isLiveOnEntryDef(UpperDef))
+        continue;
+      auto *DefInst = Def->getMemoryInst();
+      auto *UpperInst = UpperDef->getMemoryInst();
+      auto MaybeUpperLoc = getLocForWriteEx(UpperInst);
+      if (!MaybeUpperLoc || !DefInst->isIdenticalTo(UpperInst) ||
+          isReadClobber(*MaybeUpperLoc, DefInst))
+        continue;
+      deleteDeadInstruction(DefInst);
+      NumRedundantStores++;
+      MadeChange = true;
+    }
+    return MadeChange;
+  }
 };
 
 static bool eliminateDeadStores(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
@@ -2102,6 +2128,7 @@
     }
   }
 
+  MadeChange |= State.eliminateRedundantStoresOfExistingValues();
   if (EnablePartialOverwriteTracking)
     for (auto &KV : State.IOLs)
       MadeChange |= removePartiallyOverlappedStores(State.DL, KV.second, TLI);
diff --git a/llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll b/llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll
--- a/llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/stores-of-existing-values.ll
@@ -7,7 +7,7 @@
 
 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i64, i1 immarg)
 
-; Test case for PR16520. The store in %if.then is dead, because the same value
+; Test case for PR16520. The store in %if.then is redundant, because the same value
 ; has been stored earlier to the same location.
 define void @test1_pr16520(i1 %b, i8* nocapture %r) {
 ; CHECK-LABEL: @test1_pr16520(
@@ -15,7 +15,6 @@
 ; CHECK-NEXT:    store i8 1, i8* [[R:%.*]], align 1
 ; CHECK-NEXT:    br i1 [[B:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    store i8 1, i8* [[R]], align 1
 ; CHECK-NEXT:    tail call void @fn_mayread_or_clobber()
 ; CHECK-NEXT:    br label [[IF_END:%.*]]
 ; CHECK:       if.else:
@@ -42,8 +41,6 @@
 }
 
 declare void @fn_mayread_or_clobber()
-
-
 declare void @fn_readonly() readonly
 
 define void @test2(i1 %b, i8* nocapture %r) {
@@ -58,7 +55,6 @@
 ; CHECK-NEXT:    tail call void @fn_readonly()
 ; CHECK-NEXT:    br label [[IF_END]]
 ; CHECK:       if.end:
-; CHECK-NEXT:    store i8 1, i8* [[R]], align 1
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -78,6 +74,39 @@
   ret void
 }
 
+; Make sure volatile stores are not removed.
+define void @test2_volatile(i1 %b, i8* nocapture %r) {
+; CHECK-LABEL: @test2_volatile(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    store volatile i8 1, i8* [[R:%.*]], align 1
+; CHECK-NEXT:    br i1 [[B:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    tail call void @fn_readonly()
+; CHECK-NEXT:    br label [[IF_END:%.*]]
+; CHECK:       if.else:
+; CHECK-NEXT:    tail call void @fn_readonly()
+; CHECK-NEXT:    br label [[IF_END]]
+; CHECK:       if.end:
+; CHECK-NEXT:    store volatile i8 1, i8* [[R]], align 1
+; CHECK-NEXT:    ret void
+;
+entry:
+  store volatile i8 1, i8* %r, align 1
+  br i1 %b, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  tail call void @fn_readonly()
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  tail call void @fn_readonly()
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  store volatile i8 1, i8* %r, align 1
+  ret void
+}
+
 define void @test3(i1 %b, i8* nocapture %r) {
 ; CHECK-LABEL: @test3(
 ; CHECK-NEXT:  entry:
@@ -185,7 +214,6 @@
 ; CHECK-NEXT:    [[C1:%.*]] = call i1 @cond()
 ; CHECK-NEXT:    br i1 [[C1]], label [[FOR_BODY:%.*]], label [[END:%.*]]
 ; CHECK:       for.body:
-; CHECK-NEXT:    store i32 1, i32* [[P]], align 4
 ; CHECK-NEXT:    [[LV:%.*]] = load i32, i32* [[P]], align 4
 ; CHECK-NEXT:    br label [[FOR_HEADER]]
 ; CHECK:       end:
@@ -220,7 +248,6 @@
 ; CHECK:       bb2:
 ; CHECK-NEXT:    ret void
 ; CHECK:       bb3:
-; CHECK-NEXT:    store i32 0, i32* [[P]], align 4
 ; CHECK-NEXT:    ret void
 ;
   store i32 0, i32* %P
@@ -272,7 +299,6 @@
 ; CHECK-NEXT:    call void @fn_mayread_or_clobber()
 ; CHECK-NEXT:    ret void
 ; CHECK:       bb3:
-; CHECK-NEXT:    store i32 0, i32* [[P]], align 4
 ; CHECK-NEXT:    ret void
 ;
   store i32 0, i32* %P