Index: llvm/include/llvm/Transforms/Utils/FunctionComparator.h
===================================================================
--- llvm/include/llvm/Transforms/Utils/FunctionComparator.h
+++ llvm/include/llvm/Transforms/Utils/FunctionComparator.h
@@ -332,7 +332,8 @@
   int cmpOrderings(AtomicOrdering L, AtomicOrdering R) const;
   int cmpInlineAsm(const InlineAsm *L, const InlineAsm *R) const;
   int cmpAttrs(const AttributeList L, const AttributeList R) const;
-  int cmpRangeMetadata(const MDNode *L, const MDNode *R) const;
+  int cmpMetadata(const MDNode *L, const MDNode *R) const;
+  int cmpInstMetadata(Instruction const *L, Instruction const *R) const;
   int cmpOperandBundlesSchema(const CallBase &LCS, const CallBase &RCS) const;
 
   /// Compare two GEPs for equivalent pointer arithmetic.
Index: llvm/lib/Transforms/Utils/FunctionComparator.cpp
===================================================================
--- llvm/lib/Transforms/Utils/FunctionComparator.cpp
+++ llvm/lib/Transforms/Utils/FunctionComparator.cpp
@@ -157,16 +157,13 @@
   return 0;
 }
 
-int FunctionComparator::cmpRangeMetadata(const MDNode *L,
-                                         const MDNode *R) const {
+int FunctionComparator::cmpMetadata(const MDNode *L, const MDNode *R) const {
   if (L == R)
     return 0;
   if (!L)
     return -1;
   if (!R)
     return 1;
-  // Range metadata is a sequence of numbers. Make sure they are the same
-  // sequence.
   // TODO: Note that as this is metadata, it is possible to drop and/or merge
   // this data when considering functions to merge. Thus this comparison would
   // return 0 (i.e. equivalent), but merging would become more complicated
@@ -176,14 +173,48 @@
   if (int Res = cmpNumbers(L->getNumOperands(), R->getNumOperands()))
     return Res;
   for (size_t I = 0; I < L->getNumOperands(); ++I) {
+    // TODO: the following routine coerce the metadata contents into numbers
+    // before comparison.
+    // It ignores any other cases, so that the metadata nodes are considered
+    // equal even though this is not correct.
+    // We should structurally compare the metadata nodes to be perfect here.
     ConstantInt *LLow = mdconst::extract<ConstantInt>(L->getOperand(I));
     ConstantInt *RLow = mdconst::extract<ConstantInt>(R->getOperand(I));
+    if (LLow == RLow)
+      continue;
+    if (!LLow)
+      return -1;
+    if (!RLow)
+      return 1;
     if (int Res = cmpAPInts(LLow->getValue(), RLow->getValue()))
       return Res;
   }
   return 0;
 }
 
+int FunctionComparator::cmpInstMetadata(Instruction const *L,
+                                        Instruction const *R) const {
+  /// These metadata affects the other optimization passes by making assertions
+  /// or constraints.
+  /// Values that carries different expectations should be considered different.
+  SmallVector<std::pair<unsigned, MDNode *>> MDL, MDR;
+  L->getAllMetadataOtherThanDebugLoc(MDL);
+  R->getAllMetadataOtherThanDebugLoc(MDR);
+  if (MDL.size() > MDR.size())
+    return 1;
+  else if (MDL.size() < MDR.size())
+    return -1;
+  for (size_t I = 0, N = MDL.size(); I < N; ++I) {
+    auto const [KeyL, ML] = MDL[I];
+    auto const [KeyR, MR] = MDR[I];
+    if (int Res = cmpNumbers(KeyL, KeyR))
+      return Res;
+    if (int Res = cmpMetadata(ML, MR))
+      return Res;
+  }
+  return 0;
+}
+
 int FunctionComparator::cmpOperandBundlesSchema(const CallBase &LCS,
                                                 const CallBase &RCS) const {
   assert(LCS.getOpcode() == RCS.getOpcode() && "Can't compare otherwise!");
@@ -586,9 +617,7 @@
     if (int Res = cmpNumbers(LI->getSyncScopeID(),
                              cast<LoadInst>(R)->getSyncScopeID()))
       return Res;
-    return cmpRangeMetadata(
-        LI->getMetadata(LLVMContext::MD_range),
-        cast<LoadInst>(R)->getMetadata(LLVMContext::MD_range));
+    return cmpInstMetadata(L, R);
   }
   if (const StoreInst *SI = dyn_cast<StoreInst>(L)) {
     if (int Res =
@@ -616,8 +645,8 @@
       if (int Res = cmpNumbers(CI->getTailCallKind(),
                                cast<CallInst>(R)->getTailCallKind()))
         return Res;
-    return cmpRangeMetadata(L->getMetadata(LLVMContext::MD_range),
-                            R->getMetadata(LLVMContext::MD_range));
+    return cmpMetadata(L->getMetadata(LLVMContext::MD_range),
+                       R->getMetadata(LLVMContext::MD_range));
   }
   if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(L)) {
     ArrayRef<unsigned> LIndices = IVI->getIndices();
Index: llvm/test/Transforms/MergeFunc/mergefunc-preserve-nonnull.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/MergeFunc/mergefunc-preserve-nonnull.ll
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=mergefunc -S < %s | FileCheck %s
+
+; This test makes sure that the mergefunc pass does not merge functions
+; that have different nonnull assertions.
+
+%1 = type ptr
+
+define void @f1(ptr %0, ptr %1) {
+; CHECK-LABEL: @f1(
+; CHECK-NEXT:    [[TMP3:%.*]] = load ptr, ptr [[TMP1:%.*]], align 8, !nonnull !0
+; CHECK-NEXT:    store ptr [[TMP3]], ptr [[TMP0:%.*]], align 8
+; CHECK-NEXT:    ret void
+;
+  %3 = load ptr, ptr %1, align 8, !nonnull !0
+  store ptr %3, ptr %0, align 8
+  ret void
+}
+
+define void @f2(ptr %0, ptr %1) {
+; CHECK-LABEL: @f2(
+; CHECK-NEXT:    [[TMP3:%.*]] = load ptr, ptr [[TMP1:%.*]], align 8
+; CHECK-NEXT:    store ptr [[TMP3]], ptr [[TMP0:%.*]], align 8
+; CHECK-NEXT:    ret void
+;
+  %3 = load ptr, ptr %1, align 8
+  store ptr %3, ptr %0, align 8
+  ret void
+}
+
+define void @f3(ptr %0, ptr %1) {
+; CHECK-LABEL: @f3(
+; CHECK-NEXT:    [[TMP3:%.*]] = load ptr, ptr [[TMP1:%.*]], align 8, !noundef !0
+; CHECK-NEXT:    store ptr [[TMP3]], ptr [[TMP0:%.*]], align 8
+; CHECK-NEXT:    ret void
+;
+  %3 = load ptr, ptr %1, align 8, !noundef !0
+  store ptr %3, ptr %0, align 8
+  ret void
+}
+
+define void @f4(ptr %0, ptr %1) {
+; CHECK-LABEL: @f4(
+; CHECK-NEXT:    tail call void @f3(ptr [[TMP0:%.*]], ptr [[TMP1:%.*]])
+; CHECK-NEXT:    ret void
+;
+  %3 = load ptr, ptr %1, align 8, !noundef !0, !dbg !1
+  store ptr %3, ptr %0, align 8
+  ret void
+}
+
+!0 = !{}
+!1 = !{}