[Asan] Unpoison red zones even if use-after-scope was disabled with runtime flag

[vitalybuka]

Summary

PR27453

[eugenis]

LGTM with a test

[vitalybuka]

tests

[eugenis]

test/Instrumentation/AddressSanitizer/lifetime-uar-uas.ll

32 ↗

(On Diff #68080)

I thought the syntax is "CHECK-UAS-NEXT" ?

[vitalybuka]

test

lib/Transforms/Instrumentation/AddressSanitizer.cpp

Value *BasePlus2 = IRB.CreateIntToPtr(
       IntptrPtrTy);
   IRB.CreateStore(IRB.CreatePointerCast(&F, IntptrTy), BasePlus2);
 
   // Poison the stack redzones at the entry.
   Value *ShadowBase = ASan.memToShadow(LocalStackBase, IRB);
   poisonRedZones(L.ShadowBytes, IRB, ShadowBase, true);
 
   auto UnpoisonStack = [&](IRBuilder<> &IRB) {
+    // Do this always as poisonAlloca can be disabled with
+    // detect_stack_use_after_scope=0.
+    poisonRedZones(L.ShadowBytes, IRB, ShadowBase, false);
     if (HavePoisonedStaticAllocas) {
       // If we poisoned some allocas in llvm.lifetime analysis,
       // unpoison whole stack frame now.
       poisonAlloca(LocalStackBase, LocalStackSize, IRB, false);
-    } else {
-      poisonRedZones(L.ShadowBytes, IRB, ShadowBase, false);
     }
   };
 
   // (Un)poison the stack before all ret instructions.
   for (auto Ret : RetVec) {
     IRBuilder<> IRBRet(Ret);
     // Mark the current frame as retired.
     IRBRet.CreateStore(ConstantInt::get(IntptrTy, kRetiredStackFrameMagic),