[NFC] [MTE] only do one pass over allocas for stack tagging.

[eugenis]

LGTM

llvm/lib/Target/AArch64/AArch64StackTagging.cpp

memtag::StackInfoBuilder SIB(
       [this](const AllocaInst &AI) { return isInterestingAlloca(AI); });
   for (Instruction &I : instructions(F))
     SIB.visit(I);
   memtag::StackInfo &SInfo = SIB.get();
 
   if (SInfo.AllocasToInstrument.empty())
     return false;
 
-  for (auto &I : SInfo.AllocasToInstrument) {
-    memtag::AllocaInfo &Info = I.second;
-    assert(Info.AI && isInterestingAlloca(*Info.AI));
-    auto *PrevAI = Info.AI;
-    if (memtag::alignAndPadAlloca(Info, kTagGranuleSize))
-      PrevAI->eraseFromParent();
-  }
-
   std::unique_ptr<DominatorTree> DeleteDT;
   DominatorTree *DT = nullptr;
   if (auto *P = getAnalysisIfAvailable<DominatorTreeWrapperPass>())
     DT = &P->getDomTree();
 
   if (DT == nullptr && (SInfo.AllocasToInstrument.size() > 1 ||
                         !F->hasFnAttribute(Attribute::OptimizeNone))) {
     DeleteDT = std::make_unique<DominatorTree>(*F);
bool AArch64StackTagging::runOnFunction(Function &Fn) {
 
   SetTagFunc =
       Intrinsic::getDeclaration(F->getParent(), Intrinsic::aarch64_settag);
 
   Instruction *Base = insertBaseTaggedPointer(SInfo.AllocasToInstrument, DT);
 
   int NextTag = 0;
   for (auto &I : SInfo.AllocasToInstrument) {
-    const memtag::AllocaInfo &Info = I.second;
+    memtag::AllocaInfo &Info = I.second;
+    assert(Info.AI && isInterestingAlloca(*Info.AI));
+    auto *PrevAI = Info.AI;
+    if (memtag::alignAndPadAlloca(Info, kTagGranuleSize))
+      PrevAI->eraseFromParent();
     AllocaInst *AI = Info.AI;
     int Tag = NextTag;
     NextTag = (NextTag + 1) % 16;
     // Replace alloca with tagp(alloca).
     IRBuilder<> IRB(Info.AI->getNextNode());
     Function *TagP = Intrinsic::getDeclaration(
         F->getParent(), Intrinsic::aarch64_tagp, {Info.AI->getType()});
     Instruction *TagPCall =