[AMDGPU] Return better Changed status from AMDGPUPerfHintAnalysis

[piotr]

LGTM

llvm/lib/Target/AMDGPU/AMDGPUPerfHintAnalysis.cpp

bool AMDGPUPerfHint::runOnFunction(Function &F) {
   const AMDGPUPerfHintAnalysis::FuncInfo *Info = visit(F);
 
   LLVM_DEBUG(dbgs() << F.getName() << " MemInst cost: " << Info->MemInstCost
                     << '\n'
                     << " IAMInst cost: " << Info->IAMInstCost << '\n'
                     << " LSMInst cost: " << Info->LSMInstCost << '\n'
                     << " TotalInst cost: " << Info->InstCost << '\n');
 
+  bool Changed = false;
+
   if (isMemBound(*Info)) {
     LLVM_DEBUG(dbgs() << F.getName() << " is memory bound\n");
     NumMemBound++;
     F.addFnAttr("amdgpu-memory-bound", "true");
+    Changed = true;
   }
 
   if (AMDGPU::isEntryFunctionCC(F.getCallingConv()) && needLimitWave(*Info)) {
     LLVM_DEBUG(dbgs() << F.getName() << " needs limit wave\n");
     NumLimitWave++;
     F.addFnAttr("amdgpu-wave-limiter", "true");
+    Changed = true;
   }
 
-  return true;
+  return Changed;
 }
 
 bool AMDGPUPerfHint::isMemBound(const AMDGPUPerfHintAnalysis::FuncInfo &FI) {
   return FI.MemInstCost * 100 / FI.InstCost > MemBoundThresh;
 }
 
 bool AMDGPUPerfHint::needLimitWave(const AMDGPUPerfHintAnalysis::FuncInfo &FI) {
   return ((FI.MemInstCost + FI.IAMInstCost * IAWeight +