[SamplePGO] Minor efficiency improvement in samplePGO ICP

[tejohnson]

Summary

When attaching prof metadata to promoted direct calls in SamplePGO
mode, no need to construct and use a SmallVector to pass a single count
to the ArrayRef parameter, we can simply use a brace-enclosed init list.

This made a small but consistent improvement for a ThinLTO backend
compile I was measuring.

[wmi]

LGTM. There is such place in SampleProfileLoader pass. I will do the same for it.

[tejohnson]

Ugh sorry for committing before your LGTM - I saw the LGTM come in from you on the other patch but committed this one instead! Will leave it since you subsequently LGTM'ed.

lib/Transforms/Instrumentation/IndirectCallPromotion.cpp

Instruction *llvm::pgo::promoteIndirectCall(Instruction *Inst,
   MDBuilder MDB(Inst->getContext());
   MDNode *BranchWeights = MDB.createBranchWeights(
       scaleBranchCount(Count, Scale), scaleBranchCount(ElseCount, Scale));
 
   Instruction *NewInst =
       promoteCallWithIfThenElse(CallSite(Inst), DirectCallee, BranchWeights);
 
   if (AttachProfToDirectCall) {
-    SmallVector<uint32_t, 1> Weights;
-    Weights.push_back(Count);
     MDBuilder MDB(NewInst->getContext());
-    NewInst->setMetadata(LLVMContext::MD_prof, MDB.createBranchWeights(Weights));
+    NewInst->setMetadata(
+        LLVMContext::MD_prof,
+        MDB.createBranchWeights({static_cast<uint32_t>(Count)}));
   }
 
   using namespace ore;
 
   if (ORE)
     ORE->emit([&]() {
       return OptimizationRemark(DEBUG_TYPE, "Promoted", Inst)
              << "Promote indirect call to " << NV("DirectCallee", DirectCallee)