diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2217,6 +2217,31 @@
     }
   }
 
+  // Check that each user of each old PHI node is something that we can
+  // rewrite, so that all of the old PHI nodes can be cleaned up afterwards.
+  for (auto *OldPN : OldPhiNodes) {
+    for (User *V : OldPN->users()) {
+      if (auto *SI = dyn_cast<StoreInst>(V)) {
+        if (!SI->isSimple() || SI->getOperand(0) != OldPN)
+          return nullptr;
+      } else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
+        // Verify it's a B->A cast.
+        Type *TyB = BCI->getOperand(0)->getType();
+        Type *TyA = BCI->getType();
+        if (TyA != DestTy || TyB != SrcTy)
+          return nullptr;
+      } else if (auto *PHI = dyn_cast<PHINode>(V)) {
+        // As long as the user is another old PHI node, then even if we don't
+        // rewrite it, the PHI web we're considering won't have any users
+        // outside itself, so it'll be dead.
+        if (OldPhiNodes.count(PHI) == 0)
+          return nullptr;
+      } else {
+        return nullptr;
+      }
+    }
+  }
+
   // For each old PHI node, create a corresponding new PHI node with a type A.
   SmallDenseMap<PHINode *, PHINode *> NewPNodes;
   for (auto *OldPN : OldPhiNodes) {
@@ -2261,24 +2286,25 @@
     PHINode *NewPN = NewPNodes[OldPN];
     for (User *V : OldPN->users()) {
       if (auto *SI = dyn_cast<StoreInst>(V)) {
-        if (SI->isSimple() && SI->getOperand(0) == OldPN) {
-          Builder.SetInsertPoint(SI);
-          auto *NewBC =
-            cast<BitCastInst>(Builder.CreateBitCast(NewPN, SrcTy));
-          SI->setOperand(0, NewBC);
-          Worklist.Add(SI);
-          assert(hasStoreUsersOnly(*NewBC));
-        }
+        assert(SI->isSimple() && SI->getOperand(0) == OldPN);
+        Builder.SetInsertPoint(SI);
+        auto *NewBC =
+          cast<BitCastInst>(Builder.CreateBitCast(NewPN, SrcTy));
+        SI->setOperand(0, NewBC);
+        Worklist.Add(SI);
+        assert(hasStoreUsersOnly(*NewBC));
       }
       else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
-        // Verify it's a B->A cast.
         Type *TyB = BCI->getOperand(0)->getType();
         Type *TyA = BCI->getType();
-        if (TyA == DestTy && TyB == SrcTy) {
-          Instruction *I = replaceInstUsesWith(*BCI, NewPN);
-          if (BCI == &CI)
-            RetVal = I;
-        }
+        assert(TyA == DestTy && TyB == SrcTy);
+        Instruction *I = replaceInstUsesWith(*BCI, NewPN);
+        if (BCI == &CI)
+          RetVal = I;
+      } else if (auto *PHI = dyn_cast<PHINode>(V)) {
+        assert(OldPhiNodes.count(PHI) > 0);
+      } else {
+        llvm_unreachable("all uses should be handled");
       }
     }
   }
diff --git a/llvm/test/Transforms/InstCombine/pr44242.ll b/llvm/test/Transforms/InstCombine/pr44242.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr44242.ll
@@ -0,0 +1,21 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+; Check that we don't create two redundant phi nodes when %val is used in a
+; form where we can't rewrite it in terms of the new phi node.
+define float @f(i32 %x, float %y) {
+entry:
+  %cond = icmp sgt i32 %x, 0
+  br i1 %cond, label %then, label %else
+then:
+  br label %end
+else:
+  %y_casted = bitcast float %y to i32
+  br label %end
+end:
+  %val = phi i32 [ 0, %then ], [ %y_casted, %else ]
+; CHECK-NOT: phi float
+  %casted = bitcast i32 %val to float
+  %cond2 = icmp ne i32 %val, 0
+  %result = select i1 %cond2, float %casted, float 42.
+  ret float %result
+}