[clang] Fix invalid comparator in tablegen

[EricWF]

Summary

The current version of the comparator does not introduce a strict weak ordering.

[sdesmalen]

LGTM, did this comparison introduce any non-determinism?

[EricWF]

In D78323#1987596, @sdesmalen wrote:

LGTM, did this comparison introduce any non-determinism?

Potentially, but I observed the issue using libc++'s debug mode.
I'm unsure if the current inputs would have caused libc++ to read past the end of the vector.

[EricWF]

af2968e37f4c95846ffe287b64a4fcd72c765bee

[fowles]

LGTM

clang/utils/TableGen/SveEmitter.cpp

 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/TableGen/Record.h"
 #include "llvm/TableGen/Error.h"
 #include <string>
 #include <sstream>
 #include <set>
 #include <cctype>
+#include <tuple>
 
 using namespace llvm;
 
 enum ClassKind {
   ClassNone,
   ClassS,     // signed/unsigned, e.g., "_s8", "_u8" suffix
   ClassG,     // Overloaded name without type suffix
 };
void SVEEmitter::createHeader(raw_ostream &OS) {
 
   // Sort intrinsics in header file by following order/priority:
   // - Architectural guard (i.e. does it require SVE2 or SVE2_AES)
   // - Class (is intrinsic overloaded or not)
   // - Intrinsic name
   std::stable_sort(
       Defs.begin(), Defs.end(), [](const std::unique_ptr<Intrinsic> &A,
                                    const std::unique_ptr<Intrinsic> &B) {
-        return A->getGuard() < B->getGuard() ||
-               (unsigned)A->getClassKind() < (unsigned)B->getClassKind() ||
-               A->getName() < B->getName();
+        auto ToTuple = [](const std::unique_ptr<Intrinsic> &I) {
+          return std::make_tuple(I->getGuard(), (unsigned)I->getClassKind(), I->getName());
+        };
+        return ToTuple(A) < ToTuple(B);
       });
 
   StringRef InGuard = "";
   for (auto &I : Defs) {
     // Emit #endif/#if pair if needed.
     if (I->getGuard() != InGuard) {
       if (!InGuard.empty())
         OS << "#endif  //" << InGuard << "\n";