Index: clang/lib/AST/ASTContext.cpp
===================================================================
--- clang/lib/AST/ASTContext.cpp
+++ clang/lib/AST/ASTContext.cpp
@@ -7102,6 +7102,21 @@
   case BuiltinType::Int128:
   case BuiltinType::UInt128:
     return 7 + (getIntWidth(Int128Ty) << 3);
+
+  // "The ranks of char8_t, char16_t, char32_t, and wchar_t equal the ranks of
+  // their underlying types" [c++20 conv.rank]
+  case BuiltinType::Char8:
+    return getIntegerRank(UnsignedCharTy.getTypePtr());
+  case BuiltinType::Char16:
+    return getIntegerRank(
+        getFromTargetType(Target->getChar16Type()).getTypePtr());
+  case BuiltinType::Char32:
+    return getIntegerRank(
+        getFromTargetType(Target->getChar32Type()).getTypePtr());
+  case BuiltinType::WChar_S:
+  case BuiltinType::WChar_U:
+    return getIntegerRank(
+        getFromTargetType(Target->getWCharType()).getTypePtr());
   }
 }
 
Index: clang/test/SemaCXX/vector.cpp
===================================================================
--- clang/test/SemaCXX/vector.cpp
+++ clang/test/SemaCXX/vector.cpp
@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -flax-vector-conversions=all -triple x86_64-apple-darwin10 -fsyntax-only -verify %s
 // RUN: %clang_cc1 -flax-vector-conversions=all -triple x86_64-apple-darwin10 -fsyntax-only -verify -std=c++98 %s
 // RUN: %clang_cc1 -flax-vector-conversions=all -triple x86_64-apple-darwin10 -fsyntax-only -verify -std=c++11 %s
+// RUN: %clang_cc1 -flax-vector-conversions=all -triple x86_64-apple-darwin10 -fsyntax-only -verify -std=c++20 %s
 // RUN: %clang_cc1 -flax-vector-conversions=integer -triple x86_64-apple-darwin10 -fsyntax-only -verify %s -DNO_LAX_FLOAT
 // RUN: %clang_cc1 -flax-vector-conversions=none -triple x86_64-apple-darwin10 -fsyntax-only -verify %s -DNO_LAX_FLOAT -DNO_LAX_INT
 
@@ -530,3 +531,17 @@
   S<int, 16> s;
 }
 } // namespace PR48540
+
+#if __cplusplus >= 202002L // C++20 or later
+// Don't crash due to missing integer ranks.
+char8_t v1 __attribute__((vector_size(16)));
+char16_t v2 __attribute__((vector_size(16)));
+char32_t v3 __attribute__((vector_size(16)));
+wchar_t v4 __attribute__((vector_size(16)));
+void triggerIntegerRankCheck() {
+  auto b1 = (v1 >= 0x12);
+  auto b2 = (v2 >= 0x12);
+  auto b3 = (v3 >= 0x12);
+  auto b4 = (v4 >= 0x12);
+}
+#endif