Let the target adjust physical output- and anti-deps

[frasercrmck]

Summary

This is potentially required by targets for correctness, or at least for optimization purposes.

Let me know what you think. This is necessary for our downstream target as we have a complicated per-operand scheduling model. However, as I don't think it's too controversial I thought I would push it back upstream.

[rampitec]

LGTM. Since we have adjustSchedDependency() there is no reason to use it selectively.

[frasercrmck]

rebase

llvm/lib/CodeGen/ScheduleDAGInstrs.cpp

 void ScheduleDAGInstrs::addPhysRegDeps(SUnit *SU, unsigned OperIdx) {
   MachineInstr *MI = SU->getInstr();
   MachineOperand &MO = MI->getOperand(OperIdx);
   Register Reg = MO.getReg();
   // We do not need to track any dependencies for constant registers.
   if (MRI.isConstantPhysReg(Reg))
     return;
 
+  const TargetSubtargetInfo &ST = MF.getSubtarget();
+
   // Optionally add output and anti dependencies. For anti
   // dependencies we use a latency of 0 because for a multi-issue
   // target we want to allow the defining instruction to issue
   // in the same cycle as the using instruction.
   // TODO: Using a latency of 1 here for output dependencies assumes
   //       there's no cost for reusing registers.
   SDep::Kind Kind = MO.isUse() ? SDep::Anti : SDep::Output;
   for (MCRegAliasIterator Alias(Reg, TRI, true); Alias.isValid(); ++Alias) {
     if (!Defs.contains(*Alias))
       continue;
     for (Reg2SUnitsMap::iterator I = Defs.find(*Alias); I != Defs.end(); ++I) {
       SUnit *DefSU = I->SU;
       if (DefSU == &ExitSU)
         continue;
       if (DefSU != SU &&
           (Kind != SDep::Output || !MO.isDead() ||
            !DefSU->getInstr()->registerDefIsDead(*Alias))) {
-        if (Kind == SDep::Anti)
-          DefSU->addPred(SDep(SU, Kind, /*Reg=*/*Alias));
-        else {
-          SDep Dep(SU, Kind, /*Reg=*/*Alias);
+        if (Kind != SDep::Anti)
           Dep.setLatency(
             SchedModel.computeOutputLatency(MI, OperIdx, DefSU->getInstr()));
-          DefSU->addPred(Dep);
-        }
-      }
-    }
-  }
+        ST.adjustSchedDependency(SU, OperIdx, DefSU, I->OpIdx, Dep);
 
   if (!MO.isDef()) {
     SU->hasPhysRegUses = true;
     // Either insert a new Reg2SUnits entry with an empty SUnits list, or
     // retrieve the existing SUnits list for this register's uses.
     // Push this SUnit on the use list.
     Uses.insert(PhysRegSUOper(SU, OperIdx, Reg));
     if (RemoveKillFlags)