[PATCH] D18427: CodeGen: Add DetectDeadLanes pass.

[Matthias Braun via llvm-commits]

MatzeB added inline comments.

================
Comment at: lib/CodeGen/DetectDeadLanes.cpp:253
@@ +252,3 @@
+      DefinedLanes &= ~TRI->getSubRegIndexLaneMask(SubIdx);
+    }
+    break;
----------------
qcolombet wrote:
> I know it does not use any sub-register liveness.
> 
> What I am saying is without that pass, the coalescer might expose dead defs it was not expecting and cause later crashes.
> I.e., if I understood correctly, this pass should always run to avoid potential crashes, right?
Without subregister liveness the coalescer is not able to recognize these dead definitions, so from a correctness perspective we only need the pass for subregister liveness enabled targets.


Repository:
  rL LLVM

http://reviews.llvm.org/D18427