Remove useMachineScheduler and replace it with subtarget options
that control, individually, all of the disparate things it was
controlling.

At the same time move a FIXME in the Hexagon port to a new
subtarget function that will enable a user of the machine
scheduler to avoid using the source scheduler for pre-RA-scheduling.
The FIXME would have this removed, but involves either testcase
changes or adding -pre-RA-sched=source to a few testcases.

llvm-svn: 231980
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index a0cd6ff..97abe32 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -292,7 +292,8 @@
     const TargetLowering *TLI = IS->TLI;
     const TargetSubtargetInfo &ST = IS->MF->getSubtarget();
 
-    if (OptLevel == CodeGenOpt::None || ST.useMachineScheduler() ||
+    if (OptLevel == CodeGenOpt::None ||
+        (ST.enableMachineScheduler() && ST.enableMachineSchedDefaultSched()) ||
         TLI->getSchedulingPreference() == Sched::Source)
       return createSourceListDAGScheduler(IS, OptLevel);
     if (TLI->getSchedulingPreference() == Sched::RegPressure)