[SelectionDAG] Make fast and linearize visible by clang -pre-RA-sched

ScheduleDAGFast.cpp is compiled to object file, but the ScheduleDAGFast
object file isn't linked into clang executable file as no symbol is
referred by outside. Add calling to createXxx of ScheduleDAGFast.cpp,
then the ScheduleDAGFast object file will be linked into clang
executable file. The static RegisterScheduler will register scheduler
fast and linearize at clang boot time.

Reviewed By: pengfei

Differential Revision: https://reviews.llvm.org/D101601

include/llvm/CodeGen/TargetLowering.h

@@ -94,14 +94,16 @@ class Value;
 
 namespace Sched {
 
-  enum Preference {
-    None,             // No preference
-    Source,           // Follow source order.
-    RegPressure,      // Scheduling for lowest register pressure.
-    Hybrid,           // Scheduling for both latency and register pressure.
-    ILP,              // Scheduling for ILP in low register pressure mode.
-    VLIW              // Scheduling for VLIW targets.
-  };
+enum Preference {
+  None,        // No preference
+  Source,      // Follow source order.
+  RegPressure, // Scheduling for lowest register pressure.
+  Hybrid,      // Scheduling for both latency and register pressure.
+  ILP,         // Scheduling for ILP in low register pressure mode.
+  VLIW,        // Scheduling for VLIW targets.
+  Fast,        // Fast suboptimal list scheduling
+  Linearize    // Linearize DAG, no scheduling
+};
 
 } // end namespace Sched
 

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -270,6 +270,10 @@ namespace llvm {
       return createHybridListDAGScheduler(IS, OptLevel);
     if (TLI->getSchedulingPreference() == Sched::VLIW)
       return createVLIWDAGScheduler(IS, OptLevel);
+    if (TLI->getSchedulingPreference() == Sched::Fast)
+      return createFastDAGScheduler(IS, OptLevel);
+    if (TLI->getSchedulingPreference() == Sched::Linearize)
+      return createDAGLinearizer(IS, OptLevel);
     assert(TLI->getSchedulingPreference() == Sched::ILP &&
            "Unknown sched type!");
     return createILPListDAGScheduler(IS, OptLevel);