[BOLT] Fix non-determinism in shrink wrapping

Summary:
Iterating over SmallPtrSet is non-deterministic. Change it to
SmallSetVector. Similarly, do not sort a vector of ProgramPoint when
computing the dominance frontier, as ProgramPoint uses the pointer value
to determine order. Use a SmallSetVector there too to avoid duplicates
instead of sorting + uniqueing.

(cherry picked from FBD14992085)

bolt/src/Passes/DominatorAnalysis.h

@@ -39,30 +39,28 @@ class DominatorAnalysis
       : InstrsDataflowAnalysis<DominatorAnalysis<Backward>, Backward>(BC, BF) {}
   virtual ~DominatorAnalysis() {}
 
-  SmallVector<ProgramPoint, 4> getDominanceFrontierFor(const MCInst &Dom) {
-    SmallVector<ProgramPoint, 4> Result;
+  SmallSetVector<ProgramPoint, 4> getDominanceFrontierFor(const MCInst &Dom) {
+    SmallSetVector<ProgramPoint, 4> Result;
     auto DomIdx = this->ExprToIdx[&Dom];
     assert(!Backward && "Post-dom frontier not implemented");
     for (auto &BB : this->Func) {
       bool HasDominatedPred = false;
       bool HasNonDominatedPred = false;
-      SmallVector<ProgramPoint, 4> Candidates;
+      SmallSetVector<ProgramPoint, 4> Candidates;
       this->doForAllSuccsOrPreds(BB, [&](ProgramPoint P) {
         if ((*this->getStateAt(P))[DomIdx]) {
-          Candidates.emplace_back(P);
+          Candidates.insert(P);
           HasDominatedPred = true;
           return;
         }
         HasNonDominatedPred = true;
       });
       if (HasDominatedPred && HasNonDominatedPred)
-        Result.append(Candidates.begin(), Candidates.end());
+        Result.insert(Candidates.begin(), Candidates.end());
       if ((*this->getStateAt(ProgramPoint::getLastPointAt(BB)))[DomIdx] &&
           BB.succ_begin() == BB.succ_end())
-        Result.emplace_back(ProgramPoint::getLastPointAt(BB));
+        Result.insert(ProgramPoint::getLastPointAt(BB));
     }
-    std::sort(Result.begin(), Result.end());
-    Result.erase(std::unique(Result.begin(), Result.end()), Result.end());
     return Result;
   }
 

bolt/src/Passes/ShrinkWrapping.cpp

@@ -771,7 +771,7 @@ void ShrinkWrapping::pruneUnwantedCSRs() {
 }
 
 void ShrinkWrapping::computeSaveLocations() {
-  SavePos = std::vector<SmallPtrSet<MCInst *, 4>>(BC.MRI->getNumRegs());
+  SavePos = std::vector<SmallSetVector<MCInst *, 4>>(BC.MRI->getNumRegs());
   auto &RI = Info.getReachingInsnsBackwards();
   auto &DA = Info.getDominatorAnalysis();
   auto &SPT = Info.getStackPointerTracking();
@@ -960,7 +960,7 @@ ShrinkWrapping::doRestorePlacement(MCInst *BestPosSave, unsigned CSR,
   // In case of a critical edge, we need to create extra BBs to host restores
   // into edges transitioning to the dominance frontier, otherwise we pull these
   // restores to inside the dominated area.
-  Frontier = DA.getDominanceFrontierFor(*BestPosSave);
+  Frontier = DA.getDominanceFrontierFor(*BestPosSave).takeVector();
   DEBUG({
     dbgs() << "Dumping dominance frontier for ";
     BC.printInstruction(dbgs(), *BestPosSave);

bolt/src/Passes/ShrinkWrapping.h

@@ -306,7 +306,7 @@ class ShrinkWrapping {
   std::vector<int64_t> PopOffsetByReg;
   std::vector<MCPhysReg> DomOrder;
   CalleeSavedAnalysis CSA;
-  std::vector<SmallPtrSet<MCInst *, 4>> SavePos;
+  std::vector<SmallSetVector<MCInst *, 4>> SavePos;
   std::vector<uint64_t> BestSaveCount;
   std::vector<MCInst *> BestSavePos;