Index: llvm/lib/Support/RISCVISAInfo.cpp
===================================================================
--- llvm/lib/Support/RISCVISAInfo.cpp
+++ llvm/lib/Support/RISCVISAInfo.cpp
@@ -286,16 +286,17 @@
 // We rank extensions in the following order:
 // -Single letter extensions in canonical order.
 // -Unknown single letter extensions in alphabetical order.
-// -Multi-letter extensions starting with 's' in alphabetical order.
 // -Multi-letter extensions starting with 'z' sorted by canonical order of
 //  the second letter then sorted alphabetically.
+// -Multi-letter extensions starting with 's' in alphabetical order.
+// -(TODO) Multi-letter extensions starting with 'zxm' in alphabetical order.
 // -X extensions in alphabetical order.
 // These flags are used to indicate the category. The first 6 bits store the
 // single letter extension rank for single letter and multi-letter extensions
 // starting with 'z'.
 enum RankFlags {
-  RF_S_EXTENSION = 1 << 6,
-  RF_Z_EXTENSION = 1 << 7,
+  RF_Z_EXTENSION = 1 << 6,
+  RF_S_EXTENSION = 1 << 7,
   RF_X_EXTENSION = 1 << 8,
 };
 
Index: llvm/unittests/Support/RISCVISAInfoTest.cpp
===================================================================
--- llvm/unittests/Support/RISCVISAInfoTest.cpp
+++ llvm/unittests/Support/RISCVISAInfoTest.cpp
@@ -484,11 +484,8 @@
   for (const auto &Ext : Exts)
     ExtNames.push_back(Ext.first);
 
-  // FIXME: z* extensions should be ordered before s* extensions. The current
-  // ordering matches what is documented in RISCVISAInfo, but this doesn't
-  // match the ISA manual.
   // FIXME: 'l' and 'y' should be ordered after 'i', 'm', 'c'.
   EXPECT_THAT(ExtNames,
-              ElementsAre("i", "m", "l", "c", "y", "sbar", "sfoo", "zicsr",
-                          "zmfoo", "zfinx", "zzfoo", "xbar", "xfoo"));
+              ElementsAre("i", "m", "l", "c", "y", "zicsr", "zmfoo", "zfinx",
+                           "zzfoo", "sbar", "sfoo", "xbar", "xfoo"));
 }