diff --git a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -1245,6 +1245,28 @@
   llvm_unreachable("Cannot find the unknown count edge");
 }
 
+// Emit function metadata indicating PGO profile mismatch.
+static void annotateFunctionWithHashMismatch(Function &F,
+                                             LLVMContext &ctx) {
+  const char MetadataName[] = "instr_prof_hash_mismatch";
+  SmallVector<Metadata *, 2> Names;
+  // If this metadata already exists, ignore.
+  auto *Existing = F.getMetadata(LLVMContext::MD_annotation);
+  if (Existing) {
+    MDTuple *Tuple = cast<MDTuple>(Existing);
+    for (auto &N : Tuple->operands()) {
+      if (cast<MDString>(N.get())->getString() ==  MetadataName)
+        return;
+      Names.push_back(N.get());
+    }
+  }
+
+  MDBuilder MDB(ctx);
+  Names.push_back(MDB.createString(MetadataName));
+  MDNode *MD = MDTuple::get(ctx, Names);
+  F.setMetadata(LLVMContext::MD_annotation, MD);
+}
+
 // Read the profile from ProfileFileName and assign the value to the
 // instrumented BB and the edges. This function also updates ProgramMaxCount.
 // Return true if the profile are successfully read, and false on errors.
@@ -1272,6 +1294,8 @@
              (F.hasComdat() ||
               F.getLinkage() == GlobalValue::AvailableExternallyLinkage));
         LLVM_DEBUG(dbgs() << "hash mismatch (skip=" << SkipWarning << ")");
+        // Emit function metadata indicating PGO profile mismatch.
+        annotateFunctionWithHashMismatch(F, M->getContext());
       }
 
       LLVM_DEBUG(dbgs() << " IsCS=" << IsCS << "\n");
diff --git a/llvm/test/Transforms/PGOProfile/Inputs/hash_mismatch_metadata.proftext b/llvm/test/Transforms/PGOProfile/Inputs/hash_mismatch_metadata.proftext
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/PGOProfile/Inputs/hash_mismatch_metadata.proftext
@@ -0,0 +1,17 @@
+:ir
+:entry_first
+foo
+# Func Hash:
+11111
+# Num Counters:
+1
+# Counter Values:
+100
+
+bar
+# Func Hash:
+11111
+# Num Counters:
+1
+# Counter Values:
+100
diff --git a/llvm/test/Transforms/PGOProfile/hash_mismatch_metadata.ll b/llvm/test/Transforms/PGOProfile/hash_mismatch_metadata.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/PGOProfile/hash_mismatch_metadata.ll
@@ -0,0 +1,18 @@
+; RUN: llvm-profdata merge %S/Inputs/hash_mismatch_metadata.proftext -o %t.profdata
+; RUN: opt < %s -mtriple=x86_64-linux-gnu -passes=pgo-instr-use -pgo-test-profile-file=%t.profdata -S | FileCheck %s
+
+define void @foo() !annotation !1 {
+entry:
+   ret void
+}
+
+define void @bar() !annotation !2 {
+entry:
+   ret void
+}
+
+!1 = !{!"fake_metadata"}
+!2 = !{!"instr_prof_hash_mismatch"}
+
+; CHECK-DAG: !{{[0-9]+}} = !{!"fake_metadata", !"instr_prof_hash_mismatch"}
+; CHECK-DAG: !{{[0-9]+}} = !{!"instr_prof_hash_mismatch"}