[ARM] Custom machine-scheduler. NFCI.

This patch creates a customised machine-scheduler for ARM targets,
so that subsequently DAG mutations etc can be added.
Reviewed by: hahn, rengolin, rovka. 
Differential Revision: https://reviews.llvm.org/D34039

llvm-svn: 305078

llvm/lib/Target/ARM/ARMTargetMachine.cpp

@@ -37,6 +37,7 @@
 #include "llvm/CodeGen/GlobalISel/RegBankSelect.h"
 #include "llvm/CodeGen/GlobalISel/RegisterBankInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineScheduler.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/IR/Attributes.h"
@@ -389,6 +390,20 @@ public:
     return getTM<ARMBaseTargetMachine>();
   }
 
+  ScheduleDAGInstrs *
+  createMachineScheduler(MachineSchedContext *C) const override {
+    ScheduleDAGMILive *DAG = createGenericSchedLive(C);
+    // add DAG Mutations here.
+    return DAG;
+  }
+
+  ScheduleDAGInstrs *
+  createPostMachineScheduler(MachineSchedContext *C) const override {
+    ScheduleDAGMI *DAG = createGenericSchedPostRA(C);
+    // add DAG Mutations here.
+    return DAG;
+  }
+
   void addIRPasses() override;
   bool addPreISel() override;
   bool addInstSelector() override;