diff --git a/llvm/include/llvm/Support/RISCVISAInfo.h b/llvm/include/llvm/Support/RISCVISAInfo.h
--- a/llvm/include/llvm/Support/RISCVISAInfo.h
+++ b/llvm/include/llvm/Support/RISCVISAInfo.h
@@ -91,6 +91,7 @@
   static llvm::Expected<std::unique_ptr<RISCVISAInfo>>
   postProcessAndChecking(std::unique_ptr<RISCVISAInfo> &&ISAInfo);
   static std::string getTargetFeatureForExtension(StringRef Ext);
+  static unsigned getExtensionSerial(StringRef ExtName);
 
 private:
   RISCVISAInfo(unsigned XLen)
diff --git a/llvm/lib/Support/RISCVISAInfo.cpp b/llvm/lib/Support/RISCVISAInfo.cpp
--- a/llvm/lib/Support/RISCVISAInfo.cpp
+++ b/llvm/lib/Support/RISCVISAInfo.cpp
@@ -1290,3 +1290,22 @@
   return isExperimentalExtension(Name) ? "experimental-" + Name.str()
                                        : Name.str();
 }
+
+
+
+unsigned RISCVISAInfo::getExtensionSerial(StringRef ExtName) {
+  verifyTables();
+
+  unsigned Offset = 1;
+  if (stripExperimentalPrefix(ExtName))
+    Offset += sizeof(SupportedExtensions) / sizeof(SupportedExtensions[0]);
+
+  for (auto ExtInfo : {ArrayRef(SupportedExtensions),
+                       ArrayRef(SupportedExperimentalExtensions)}) {
+    auto I = llvm::lower_bound(ExtInfo, ExtName, LessExtName());
+    if (I != ExtInfo.end() && I->Name == ExtName)
+      return (I - ExtInfo.begin()) + Offset;
+  }
+
+  return 0;
+}
diff --git a/llvm/unittests/Support/RISCVISAInfoTest.cpp b/llvm/unittests/Support/RISCVISAInfoTest.cpp
--- a/llvm/unittests/Support/RISCVISAInfoTest.cpp
+++ b/llvm/unittests/Support/RISCVISAInfoTest.cpp
@@ -626,3 +626,10 @@
   EXPECT_EQ(RISCVISAInfo::getTargetFeatureForExtension(""), "");
   EXPECT_EQ(RISCVISAInfo::getTargetFeatureForExtension("zbbzihintntl"), "");
 }
+
+TEST(getExtensionSerial, RetrieveAUniqueNumberForExt) {
+  EXPECT_EQ(RISCVISAInfo::getExtensionSerial("f"), 5U);
+  EXPECT_EQ(RISCVISAInfo::getExtensionSerial("a"), 1U);
+  EXPECT_EQ(RISCVISAInfo::getExtensionSerial("foo"), 0U);
+  EXPECT_EQ(RISCVISAInfo::getExtensionSerial("experimental-zicond"), 97U);
+}