Add a new "fast" scheduler. This is currently basically just a

copy of the BURRList scheduler, but with several parts ripped
out, such as backtracking, online topological sort maintenance
(needed by backtracking), the priority queue, and Sethi-Ullman
number computation and maintenance (needed by the priority
queue). As a result of all this, it generates somewhat lower
quality code, but that's its tradeoff for running about 30%
faster than list-burr in -fast mode in many cases.

This is somewhat experimental. Moving forward, major pieces of
this can be refactored with pieces in common with
ScheduleDAGRRList.cpp.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56307 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/LinkAllCodegenComponents.h

@@ -44,6 +44,7 @@ namespace {
       (void) llvm::createBURRListDAGScheduler(NULL, NULL, NULL, false);
       (void) llvm::createTDRRListDAGScheduler(NULL, NULL, NULL, false);
       (void) llvm::createTDListDAGScheduler(NULL, NULL, NULL, false);
+      (void) llvm::createFastDAGScheduler(NULL, NULL, NULL, false);
       (void) llvm::createDefaultScheduler(NULL, NULL, NULL, false);
 
     }

include/llvm/CodeGen/ScheduleDAG.h

@@ -414,6 +414,13 @@ namespace llvm {
                                         MachineBasicBlock *BB,
                                         bool Fast);
                                         
+  /// createFastDAGScheduler - This creates a "fast" scheduler.
+  ///
+  ScheduleDAG *createFastDAGScheduler(SelectionDAGISel *IS,
+                                      SelectionDAG *DAG,
+                                      MachineBasicBlock *BB,
+                                      bool Fast);
+
   /// createDefaultScheduler - This creates an instruction scheduler appropriate
   /// for the target.
   ScheduleDAG* createDefaultScheduler(SelectionDAGISel *IS,