[PATCH] D19337: [Tail duplication] Handle source registers with subregisters

[Krzysztof Parzyszek via llvm-commits]

kparzysz added inline comments.

================
Comment at: lib/CodeGen/TailDuplicator.cpp:366
@@ -363,1 +365,3 @@
+          if (VI->second.SubReg == 0)
+            MRI->constrainRegClass(VI->second.Reg, MRI->getRegClass(Reg));
         }
----------------
qcolombet wrote:
> Why do you check for the subreg here?
> If you believe the adding constraints will not work, you should check the result of constrainRegClass and act accordingly.
This is because we are doing a replacement 
```
Reg -> VI.Reg:VI.SubReg
```
If SubReg is present, then VI.Reg belongs to a class where its sub-registers are compatible with Reg, but VI.Reg itself does not have to be.  Actually, I think that the existing code is broken.


Repository:
  rL LLVM

http://reviews.llvm.org/D19337