MI-Sched: Model "reserved" processor resources.

This allows a target to use MI-Sched as an in-order scheduler that
will model strict resource conflicts without defining a processor
itinerary. Instead, the target can now use the new per-operand machine
model and define in-order resources with BufferSize=0. For example,
this would allow restricting the type of operations that can be formed
into a dispatch group. (Normally NumMicroOps is sufficient to enforce
dispatch groups).

If the intent is to model latency in in-order pipeline, as opposed to
resource conflicts, then a resource with BufferSize=1 should be
defined instead.

This feature is only casually tested as there are no in-tree targets
using it yet. However, Hal will be experimenting with POWER7.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196517 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/ScheduleDAGInstrs.cpp

@@ -697,9 +697,15 @@ void ScheduleDAGInstrs::initSUnits() {
       for (TargetSchedModel::ProcResIter
              PI = SchedModel.getWriteProcResBegin(SC),
              PE = SchedModel.getWriteProcResEnd(SC); PI != PE; ++PI) {
-        if (SchedModel.getProcResource(PI->ProcResourceIdx)->BufferSize == 1) {
+        switch (SchedModel.getProcResource(PI->ProcResourceIdx)->BufferSize) {
+        case 0:
+          SU->hasReservedResource = true;
+          break;
+        case 1:
           SU->isUnbuffered = true;
           break;
+        default:
+          break;
         }
       }
     }