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

[Matt Arsenault via Phabricator via llvm-commits]

arsenm marked an inline comment as done.
arsenm added inline comments.


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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 =
----------------
paquette wrote:
> 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?
This comment was just copied from the other handling (still not sure why the sub-pattern case needs to be handled differently). I can just drop it. I'm not sure what it's worried about.


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

https://reviews.llvm.org/D67104