Index: llvm/trunk/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ llvm/trunk/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -95,6 +95,14 @@
                                        cl::desc("instrument stack (allocas)"),
                                        cl::Hidden, cl::init(true));
 
+static cl::opt<bool> ClUARRetagToZero(
+    "hwasan-uar-retag-to-zero",
+    cl::desc("Clear alloca tags before returning from the function to allow "
+             "non-instrumented and instrumented function calls mix. When set "
+             "to false, allocas are retagged before returning from the "
+             "function to detect use after return."),
+    cl::Hidden, cl::init(true));
+
 static cl::opt<bool> ClGenerateTagsWithCalls(
     "hwasan-generate-tags-with-calls",
     cl::desc("generate new tags with runtime library calls"), cl::Hidden,
@@ -577,6 +585,8 @@
 }
 
 Value *HWAddressSanitizer::getUARTag(IRBuilder<> &IRB, Value *StackTag) {
+  if (ClUARRetagToZero)
+    return ConstantInt::get(IntptrTy, 0);
   if (ClGenerateTagsWithCalls)
     return getNextTagWithCall(IRB);
   return IRB.CreateXor(StackTag, ConstantInt::get(IntptrTy, 0xFFU));
Index: llvm/trunk/test/Instrumentation/HWAddressSanitizer/alloca-with-calls.ll
===================================================================
--- llvm/trunk/test/Instrumentation/HWAddressSanitizer/alloca-with-calls.ll
+++ llvm/trunk/test/Instrumentation/HWAddressSanitizer/alloca-with-calls.ll
@@ -0,0 +1,22 @@
+; Test alloca instrumentation when tags are generated by HWASan function.
+;
+; RUN: opt < %s -hwasan -hwasan-generate-tags-with-calls -S | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64--linux-android"
+
+declare void @use32(i32*)
+
+define void @test_alloca() sanitize_hwaddress {
+; CHECK-LABEL: @test_alloca(
+; CHECK: %[[T1:[^ ]*]] = call i8 @__hwasan_generate_tag()
+; CHECK: %[[A:[^ ]*]] = zext i8 %[[T1]] to i64
+; CHECK: %[[B:[^ ]*]] = ptrtoint i32* %x to i64
+; CHECK: %[[C:[^ ]*]] = shl i64 %[[A]], 56
+; CHECK: or i64 %[[B]], %[[C]]
+
+entry:
+  %x = alloca i32, align 4
+  call void @use32(i32* nonnull %x)
+  ret void
+}
Index: llvm/trunk/test/Instrumentation/HWAddressSanitizer/alloca.ll
===================================================================
--- llvm/trunk/test/Instrumentation/HWAddressSanitizer/alloca.ll
+++ llvm/trunk/test/Instrumentation/HWAddressSanitizer/alloca.ll
@@ -1,8 +1,8 @@
-; Test basic address sanitizer instrumentation.
+; Test alloca instrumentation.
 ;
-; RUN: opt < %s -hwasan -S | FileCheck %s --check-prefixes=CHECK,DYNAMIC-SHADOW
-; RUN: opt < %s -hwasan -hwasan-mapping-offset=0 -S | FileCheck %s --check-prefixes=CHECK,ZERO-BASED-SHADOW
-; RUN: opt < %s -hwasan -hwasan-generate-tags-with-calls -S | FileCheck %s --check-prefix=WITH-CALLS
+; RUN: opt < %s -hwasan -S | FileCheck %s --check-prefixes=CHECK,DYNAMIC-SHADOW,NO-UAR-TAGS
+; RUN: opt < %s -hwasan -hwasan-mapping-offset=0 -S | FileCheck %s --check-prefixes=CHECK,ZERO-BASED-SHADOW,NO-UAR-TAGS
+; RUN: opt < %s -hwasan -hwasan-uar-retag-to-zero=0 -S | FileCheck %s --check-prefixes=CHECK,DYNAMIC-SHADOW,UAR-TAGS
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 target triple = "aarch64--linux-android"
@@ -32,14 +32,15 @@
 ; CHECK: call void @llvm.memset.p0i8.i64(i8* align 1 %[[X_SHADOW]], i8 %[[X_TAG2]], i64 1, i1 false)
 ; CHECK: call void @use32(i32* nonnull %[[X_HWASAN]])
 
-; CHECK: %[[X_TAG_UAR:[^ ]*]] = xor i64 %[[BASE_TAG]], 255
-; CHECK: %[[X_TAG_UAR2:[^ ]*]] = trunc i64 %[[X_TAG_UAR]] to i8
+; UAR-TAGS: %[[BASE_TAG_COMPL:[^ ]*]] = xor i64 %[[BASE_TAG]], 255
+; UAR-TAGS: %[[X_TAG_UAR:[^ ]*]] = trunc i64 %[[BASE_TAG_COMPL]] to i8
 ; CHECK: %[[E2:[^ ]*]] = ptrtoint i32* %[[X]] to i64
 ; CHECK: %[[F2:[^ ]*]] = lshr i64 %[[E2]], 4
 ; DYNAMIC-SHADOW: %[[F2_DYN:[^ ]*]] = add i64 %[[F2]], %.hwasan.shadow
 ; DYNAMIC-SHADOW: %[[X_SHADOW2:[^ ]*]] = inttoptr i64 %[[F2_DYN]] to i8*
 ; ZERO-BASED-SHADOW: %[[X_SHADOW2:[^ ]*]] = inttoptr i64 %[[F2]] to i8*
-; CHECK: call void @llvm.memset.p0i8.i64(i8* align 1 %[[X_SHADOW2]], i8 %[[X_TAG_UAR2]], i64 1, i1 false)
+; NO-UAR-TAGS: call void @llvm.memset.p0i8.i64(i8* align 1 %[[X_SHADOW2]], i8 0, i64 1, i1 false)
+; UAR-TAGS: call void @llvm.memset.p0i8.i64(i8* align 1 %[[X_SHADOW2]], i8 %[[X_TAG_UAR]], i64 1, i1 false)
 ; CHECK: ret void
 
 
@@ -48,10 +49,3 @@
   call void @use32(i32* nonnull %x)
   ret void
 }
-
-; WITH-CALLS-LABEL: @test_alloca(
-; WITH-CALLS: %[[T1:[^ ]*]] = call i8 @__hwasan_generate_tag()
-; WITH-CALLS: %[[A:[^ ]*]] = zext i8 %[[T1]] to i64
-; WITH-CALLS: %[[B:[^ ]*]] = ptrtoint i32* %x to i64
-; WITH-CALLS: %[[C:[^ ]*]] = shl i64 %[[A]], 56
-; WITH-CALLS: or i64 %[[B]], %[[C]]