MISched: Fix -misched-regpressure=0 if subreg liveness enabled

Test is waiting on fixing several more crashes in the AMDGPU scheduler
implementation with this.

llvm-svn: 362174
diff --git a/llvm/lib/CodeGen/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index 0e79741..92c051d 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -2761,8 +2761,10 @@
   MF.getSubtarget().overrideSchedPolicy(RegionPolicy, NumRegionInstrs);
 
   // After subtarget overrides, apply command line options.
-  if (!EnableRegPressure)
+  if (!EnableRegPressure) {
     RegionPolicy.ShouldTrackPressure = false;
+    RegionPolicy.ShouldTrackLaneMasks = false;
+  }
 
   // Check -misched-topdown/bottomup can force or unforce scheduling direction.
   // e.g. -misched-bottomup=false allows scheduling in both directions.