[AMDGPU] Set wait state for meta instructions to zero

It looked more reasonable to set the wait state to
zero for all non-instructions. With that we can avoid
the special handling for them in `getWaitStatesSince`
and `AdvanceCycle`. This NFC patch makes the handling
more generic.

llvm/lib/Target/AMDGPU/GCNHazardRecognizer.cpp

@@ -349,14 +349,6 @@ void GCNHazardRecognizer::AdvanceCycle() {
     return;
   }
 
-  // Do not track non-instructions which do not affect the wait states.
-  // If included, these instructions can lead to buffer overflow such that
-  // detectable hazards are missed.
-  if (CurrCycleInstr->isMetaInstruction()) {
-    CurrCycleInstr = nullptr;
-    return;
-  }
-
   if (CurrCycleInstr->isBundle()) {
     processBundle();
     return;
@@ -413,7 +405,7 @@ static int getWaitStatesSince(GCNHazardRecognizer::IsHazardFn IsHazard,
     if (IsHazard(*I))
       return WaitStates;
 
-    if (I->isInlineAsm() || I->isMetaInstruction())
+    if (I->isInlineAsm())
       continue;
 
     WaitStates += SIInstrInfo::getNumWaitStates(*I);

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -1637,7 +1637,10 @@ void SIInstrInfo::insertReturn(MachineBasicBlock &MBB) const {
 
 unsigned SIInstrInfo::getNumWaitStates(const MachineInstr &MI) {
   switch (MI.getOpcode()) {
-  default: return 1; // FIXME: Do wait states equal cycles?
+  default:
+    if (MI.isMetaInstruction())
+      return 0;
+    return 1; // FIXME: Do wait states equal cycles?
 
   case AMDGPU::S_NOP:
     return MI.getOperand(0).getImm() + 1;