Index: llvm/test/tools/llvm-reduce/reduce-operands-skip-repeated-phi-input.ll
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-reduce/reduce-operands-skip-repeated-phi-input.ll
@@ -0,0 +1,32 @@
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=operands-skip --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefixes=CHECK %s < %t
+
+; Make sure if we're replacing the value in a phi, it's replaced for
+; all repeats of the same incoming block.
+
+; CHECK-INTERESTINGNESS: switch
+; CHECK-INTERESTINGNESS: phi
+; CHECK-INTERESTINGNESS-SAME: [ %gep1, %bb1 ]
+
+; CHECK: %phi.ptr = phi ptr [ %arg1, %entry ], [ %arg1, %entry ], [ %gep1, %bb1 ]
+define void @foo(i32 %arg0, ptr %arg1, ptr %arg2) {
+entry:
+  %gep0 = getelementptr i32, ptr %arg1, i32 10
+  %gep1 = getelementptr i32, ptr %arg2, i32 12
+  switch i32 %arg0, label %ret [
+    i32 3, label %bb1
+    i32 4, label %bb2
+    i32 12, label %bb2
+  ]
+
+bb1:
+  br label %bb2
+
+bb2:
+  %phi.ptr = phi ptr [ %gep0, %entry ], [ %gep0, %entry ], [ %gep1, %bb1 ]
+  store volatile i32 0, ptr %phi.ptr
+  br label %ret
+
+ret:
+  ret void
+}
Index: llvm/tools/llvm-reduce/deltas/ReduceOperandsSkip.cpp
===================================================================
--- llvm/tools/llvm-reduce/deltas/ReduceOperandsSkip.cpp
+++ llvm/tools/llvm-reduce/deltas/ReduceOperandsSkip.cpp
@@ -212,8 +212,12 @@
       }
     });
 
-    for (std::pair<Use *, Value *> P : Replacements)
-      P.first->set(P.second);
+    for (std::pair<Use *, Value *> P : Replacements) {
+      if (PHINode *Phi = dyn_cast<PHINode>(P.first->getUser()))
+        Phi->setIncomingValueForBlock(Phi->getIncomingBlock(*P.first), P.second);
+      else
+        P.first->set(P.second);
+    }
   }
 }