[PATCH] D67104: GlobalISel/TableGen: Fix handling of EXTRACT_SUBREG constraints

[Jessica Paquette via Phabricator via llvm-commits]

paquette added inline comments.


================
Comment at: utils/TableGen/GlobalISelEmitter.cpp:3977-3978
+    //
+    // FIXME: This may introduce an extra copy if the chosen class doesn't
+    //        actually contain the subregisters.
+    const auto &SrcRCDstRCPair =
----------------
Shouldn't `getMatchingSubClassWithSubRegs` always return a class which contains the subregisters?

If `SuperClass` doesn't have an appropriate subclass, then `getMatchingSubClassWithSubRegs` should return None, no?


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67104/new/

https://reviews.llvm.org/D67104