[TableGen] Fix invalid comparison function `SizeOrder` in `getMatchingSubClassWithSubRegs`

[TaWeiTu]

Summary

Building LLVM with -DEXPENSIVE_CHECKS fails with the following error message with libstdc++ in debug mode:

Error: comparison doesn't meet irreflexive requirements, assert(!(a < a)).

The patch fixes the comparison function SizeOrder by returning false when comparing two equal items.

[TaWeiTu]

Hi @arsenm, thank you for the review! Can you commit this for me? Because I don't have the commit access yet. Thanks!

[arsenm]

In D87597#2271316, @TaWeiTu wrote:

Hi @arsenm, thank you for the review! Can you commit this for me? Because I don't have the commit access yet. Thanks!

Name and email for the author?

[TaWeiTu]

Oh, I forgot about it. --author="Ta-Wei Tu <[e-mail]>", thanks!

[arsenm]

38ecd6161993ea9632efe0c0bf304bf6c2dee98f

llvm/utils/TableGen/CodeGenRegisters.cpp

 
 Optional<std::pair<CodeGenRegisterClass *, CodeGenRegisterClass *>>
 CodeGenRegisterClass::getMatchingSubClassWithSubRegs(
     CodeGenRegBank &RegBank, const CodeGenSubRegIndex *SubIdx) const {
   auto SizeOrder = [this](const CodeGenRegisterClass *A,
                       const CodeGenRegisterClass *B) {
     // If there are multiple, identical register classes, prefer the original
     // register class.
+    if (A == B)
+      return false;
     if (A->getMembers().size() == B->getMembers().size())
       return A == this;
     return A->getMembers().size() > B->getMembers().size();
   };
 
   auto &RegClasses = RegBank.getRegClasses();
 
   // Find all the subclasses of this one that fully support the sub-register