[MTE] Instrument use-after-scope for optnone functions.

[fmayer]

Summary

We always need the Dominator and PostDominatorTree for use-after-scope.

[fmayer]

Failed Tests (2):

LLVM :: CodeGen/AArch64/O0-pipeline.ll
LLVM :: CodeGen/AArch64/O3-pipeline.ll

[fmayer]

fix test failure.

do one change at a time.

[eugenis]

LGTM

TBH I'm on the fence about whether poison-at-lifetime is an optimization vs "core functionality", but lets go with this change. The important part is not to run the analysis when the function does not have the attribute (that's what the *-pipeline tests check).

[fmayer]

In D119993#3330790, @eugenis wrote:

LGTM

TBH I'm on the fence about whether poison-at-lifetime is an optimization vs "core functionality", but lets go with this change. The important part is not to run the analysis when the function does not have the attribute (that's what the *-pipeline tests check).

I think there should be a very high bar for disabling functionality with user-visible effects as "optimizations" because it adds lots of potential for confusion. In fact, from the perspective of the resulting code, the non-UAS code is potentially more optimized than the UAS one.

llvm/lib/Target/AArch64/AArch64StackTagging.cpp

bool AArch64StackTagging::runOnFunction(Function &Fn) {
   if (SInfo.AllocasToInstrument.empty())
     return false;
 
   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))) {
+  if (DT == nullptr) {
     DeleteDT = std::make_unique<DominatorTree>(*F);
     DT = DeleteDT.get();
   }
 
   std::unique_ptr<PostDominatorTree> DeletePDT;
   PostDominatorTree *PDT = nullptr;
   if (auto *P = getAnalysisIfAvailable<PostDominatorTreeWrapperPass>())
     PDT = &P->getPostDomTree();
 
-  if (PDT == nullptr && !F->hasFnAttribute(Attribute::OptimizeNone)) {
+  if (PDT == nullptr) {
     DeletePDT = std::make_unique<PostDominatorTree>(*F);
     PDT = DeletePDT.get();
   }
 
   SetTagFunc =
       Intrinsic::getDeclaration(F->getParent(), Intrinsic::aarch64_settag);
 
   Instruction *Base = insertBaseTaggedPointer(SInfo.AllocasToInstrument, DT);