Index: llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -884,6 +884,7 @@
   };
   SmallVector<AllocaPoisonCall, 8> DynamicAllocaPoisonCallVec;
   SmallVector<AllocaPoisonCall, 8> StaticAllocaPoisonCallVec;
+  bool HasUntracedLifetimeIntrinsic = false;
 
   SmallVector<AllocaInst *, 1> DynamicAllocaVec;
   SmallVector<IntrinsicInst *, 1> StackRestoreVec;
@@ -918,6 +919,14 @@
 
     initializeCallbacks(*F.getParent());
 
+    if (HasUntracedLifetimeIntrinsic) {
+      // If there are lifetime intrinsics which couldn't be traced back to an
+      // alloca, we may not know exactly when a variable enters scope, and
+      // therefore should "fail safe" by not poisoning them.
+      StaticAllocaPoisonCallVec.clear();
+      DynamicAllocaPoisonCallVec.clear();
+    }
+
     processDynamicAllocas();
     processStaticAllocas();
 
@@ -1039,7 +1048,11 @@
       return;
     // Find alloca instruction that corresponds to llvm.lifetime argument.
     AllocaInst *AI = findAllocaForValue(II.getArgOperand(1));
-    if (!AI || !ASan.isInterestingAlloca(*AI))
+    if (!AI) {
+      HasUntracedLifetimeIntrinsic = true;
+      return;
+    }
+    if (!ASan.isInterestingAlloca(*AI))
       return;
     bool DoPoison = (ID == Intrinsic::lifetime_end);
     AllocaPoisonCall APC = {&II, AI, SizeValue, DoPoison};
Index: llvm/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll
===================================================================
--- llvm/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll
+++ llvm/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll
@@ -209,6 +209,42 @@
   ; CHECK: ret void
 }
 
+declare void @foo(i32*)
+define void @PR41481(i1 %b) sanitize_address {
+; CHECK-LABEL: @PR41481
+entry:
+  %p1 = alloca i32
+  %p2 = alloca i32
+  %q1 = bitcast i32* %p1 to i8*
+  %q2 = bitcast i32* %p2 to i8*
+  br label %bb1
+
+  ; Since we cannot account for all lifetime intrinsics in this function, we
+  ; might have missed a lifetime.start one and therefore shouldn't poison the
+  ; allocas at function entry.
+  ; ENTRY: store i64 -935356719533264399
+  ; ENTRY-UAS: store i64 -935356719533264399
+
+bb1:
+  %p = select i1 %b, i32* %p1, i32* %p2
+  %q = select i1 %b, i8*  %q1, i8*  %q2
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %q)
+  call void @foo(i32* %p)
+  br i1 %b, label %bb2, label %bb3
+
+bb2:
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %q1)
+  br label %end
+
+bb3:
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %q2)
+  br label %end
+
+end:
+  ret void
+}
+
+
 declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
 declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)