diff --git a/llvm/lib/Transforms/Scalar/MergeICmps.cpp b/llvm/lib/Transforms/Scalar/MergeICmps.cpp
--- a/llvm/lib/Transforms/Scalar/MergeICmps.cpp
+++ b/llvm/lib/Transforms/Scalar/MergeICmps.cpp
@@ -624,6 +624,18 @@
   Value *IsEqual = nullptr;
   LLVM_DEBUG(dbgs() << "Merging " << Comparisons.size() << " comparisons -> "
                     << BB->getName() << "\n");
+
+  // If there is one block that requires splitting, we do it now, i.e.
+  // just before we know we will collapse the chain. The instructions
+  // can be executed before any of the instructions in the chain.
+  const auto ToSplit =
+      std::find_if(Comparisons.begin(), Comparisons.end(),
+                   [](const BCECmpBlock &B) { return B.RequireSplit; });
+  if (ToSplit != Comparisons.end()) {
+    LLVM_DEBUG(dbgs() << "Splitting non_BCE work to header\n");
+    ToSplit->split(BB, AA);
+  }
+
   if (Comparisons.size() == 1) {
     LLVM_DEBUG(dbgs() << "Only one comparison, updating branches\n");
     Value *const LhsLoad =
@@ -633,17 +645,6 @@
     // There are no blocks to merge, just do the comparison.
     IsEqual = Builder.CreateICmpEQ(LhsLoad, RhsLoad);
   } else {
-    // If there is one block that requires splitting, we do it now, i.e.
-    // just before we know we will collapse the chain. The instructions
-    // can be executed before any of the instructions in the chain.
-    const auto ToSplit =
-        std::find_if(Comparisons.begin(), Comparisons.end(),
-                     [](const BCECmpBlock &B) { return B.RequireSplit; });
-    if (ToSplit != Comparisons.end()) {
-      LLVM_DEBUG(dbgs() << "Splitting non_BCE work to header\n");
-      ToSplit->split(BB, AA);
-    }
-
     const unsigned TotalSizeBits = std::accumulate(
         Comparisons.begin(), Comparisons.end(), 0u,
         [](int Size, const BCECmpBlock &C) { return Size + C.SizeBits(); });
diff --git a/llvm/test/Transforms/MergeICmps/X86/gep-references-bb.ll b/llvm/test/Transforms/MergeICmps/X86/gep-references-bb.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/MergeICmps/X86/gep-references-bb.ll
@@ -0,0 +1,64 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -mergeicmps -verify-dom-info | FileCheck %s
+target triple = "x86_64"
+
+%Triple = type { %Elem0, %Elem1, %Elem2 }
+%Elem0 = type { i32 }
+%Elem1 = type { i32 }
+%Elem2 = type { i32 }
+
+;; %gep does not reference an argument. Disable the optimization because
+;; otherwise the newly created gep may reference undef (after the basic block
+;; defining the pointer operand is deleted).
+define i1 @bug(%Triple* nonnull dereferenceable(12) %lhs, %Triple* nonnull dereferenceable(12) %rhs) {
+; CHECK-LABEL: @bug(
+; CHECK-NEXT:  bb02:
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr [[TRIPLE:%.*]], %Triple* [[RHS:%.*]], i64 0, i32 0
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds [[TRIPLE]], %Triple* [[LHS:%.*]], i64 0, i32 0, i32 0
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds [[TRIPLE]], %Triple* [[RHS]], i64 0, i32 0, i32 0
+; CHECK-NEXT:    [[TMP2:%.*]] = load i32, i32* [[TMP0]], align 4
+; CHECK-NEXT:    [[TMP3:%.*]] = load i32, i32* [[TMP1]], align 4
+; CHECK-NEXT:    [[TMP4:%.*]] = icmp eq i32 [[TMP2]], [[TMP3]]
+; CHECK-NEXT:    br i1 [[TMP4]], label %"bb1+bb2", label [[FINAL:%.*]]
+; CHECK:       "bb1+bb2":
+; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr inbounds [[TRIPLE]], %Triple* [[LHS]], i64 0, i32 1, i32 0
+; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr inbounds [[ELEM0:%.*]], %Elem0* [[GEP]], i64 1, i32 0
+; CHECK-NEXT:    [[CSTR:%.*]] = bitcast i32* [[TMP5]] to i8*
+; CHECK-NEXT:    [[CSTR1:%.*]] = bitcast i32* [[TMP6]] to i8*
+; CHECK-NEXT:    [[MEMCMP:%.*]] = call i32 @memcmp(i8* [[CSTR]], i8* [[CSTR1]], i64 8)
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i32 [[MEMCMP]], 0
+; CHECK-NEXT:    br label [[FINAL]]
+; CHECK:       final:
+; CHECK-NEXT:    [[RET:%.*]] = phi i1 [ [[TMP7]], %"bb1+bb2" ], [ false, [[BB02:%.*]] ]
+; CHECK-NEXT:    ret i1 [[RET]]
+;
+bb0:
+  %gep = getelementptr %Triple, %Triple* %rhs, i64 0, i32 0
+  %l0_addr = getelementptr inbounds %Triple, %Triple* %lhs, i64 0, i32 0, i32 0
+  %l0 = load i32, i32* %l0_addr, align 4
+  %r0_addr = getelementptr inbounds %Triple, %Triple* %rhs, i64 0, i32 0, i32 0
+  %r0 = load i32, i32* %r0_addr, align 4
+  %cmp0 = icmp eq i32 %l0, %r0
+  br i1 %cmp0, label %bb1, label %final
+
+bb1:                                           ; preds = %bb0
+  %l1_addr = getelementptr inbounds %Triple, %Triple* %lhs, i64 0, i32 1, i32 0
+  %l1 = load i32, i32* %l1_addr, align 4
+  %r1_addr = getelementptr inbounds %Elem0, %Elem0* %gep, i64 1, i32 0
+  %r1 = load i32, i32* %r1_addr, align 4
+  %cmp1 = icmp eq i32 %l1, %r1
+  br i1 %cmp1, label %bb2, label %final
+
+bb2:                                           ; preds = %bb1
+  %l2_addr = getelementptr inbounds %Triple, %Triple* %lhs, i64 0, i32 2, i32 0
+  %l2 = load i32, i32* %l2_addr, align 4
+  %r2_addr = getelementptr inbounds %Elem0, %Elem0* %gep, i64 2, i32 0
+  %r2 = load i32, i32* %r2_addr, align 4
+  %cmp2 = icmp eq i32 %l2, %r2
+  br label %final
+
+final:                                            ; preds = %bb2, %bb1, %bb0
+  %ret = phi i1 [ false, %bb0 ], [ false, %bb1 ], [ %cmp2, %bb2 ]
+  ret i1 %ret
+}
+