Index: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -54,6 +54,8 @@
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
 #include <algorithm>
+#include <iomanip>
+#include <sstream>
 #include <string>
 #include <system_error>
 
@@ -111,6 +113,7 @@
 static const char *const kAsanGenPrefix = "__asan_gen_";
 static const char *const kODRGenPrefix = "__odr_asan_gen_";
 static const char *const kSanCovGenPrefix = "__sancov_gen_";
+static const char *const kAsanSetShadowPrefix = "__asan_set_shadow_";
 static const char *const kAsanPoisonStackMemoryName =
     "__asan_poison_stack_memory";
 static const char *const kAsanUnpoisonStackMemoryName =
@@ -170,6 +173,10 @@
 static cl::opt<bool> ClUseAfterScope("asan-use-after-scope",
                                      cl::desc("Check stack-use-after-scope"),
                                      cl::Hidden, cl::init(false));
+static cl::opt<bool> ClExperimentalPoisoning(
+    "asan-experimental-poisoning",
+    cl::desc("Enable experimental red zones and scope poisoning"), cl::Hidden,
+    cl::init(false));
 // This flag may need to be replaced with -f[no]asan-globals.
 static cl::opt<bool> ClGlobals("asan-globals",
                                cl::desc("Handle global objects"), cl::Hidden,
@@ -613,6 +620,7 @@
 
   Function *AsanStackMallocFunc[kMaxAsanStackMallocSizeClass + 1],
       *AsanStackFreeFunc[kMaxAsanStackMallocSizeClass + 1];
+  Function *AsanSetShadowFunc[0x100] = {};
   Function *AsanPoisonStackMemoryFunc, *AsanUnpoisonStackMemoryFunc;
   Function *AsanAllocaPoisonFunc, *AsanAllocasUnpoisonFunc;
 
@@ -1924,6 +1932,17 @@
                               IntptrTy, IntptrTy, nullptr));
   }
 
+  if (ClExperimentalPoisoning) {
+    for (size_t Val : {0x00, 0xf1, 0xf2, 0xf3, 0xf5, 0xf8}) {
+      std::ostringstream Name;
+      Name << kAsanSetShadowPrefix;
+      Name << std::setw(2) << std::setfill('0') << std::hex << Val;
+      AsanSetShadowFunc[Val] =
+          checkSanitizerInterfaceFunction(M.getOrInsertFunction(
+              Name.str(), IRB.getVoidTy(), IntptrTy, IntptrTy, nullptr));
+    }
+  }
+
   AsanAllocaPoisonFunc = checkSanitizerInterfaceFunction(M.getOrInsertFunction(
       kAsanAllocaPoison, IRB.getVoidTy(), IntptrTy, IntptrTy, nullptr));
   AsanAllocasUnpoisonFunc =
Index: llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-experimental.ll
===================================================================
--- llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-experimental.ll
+++ llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-experimental.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -asan -asan-module -asan-experimental-poisoning -S | FileCheck %s
+; RUN: opt < %s -asan -asan-module -S | FileCheck --check-prefix=CHECK-OFF %s
+
+target datalayout = "e-i64:64-f80:128-s:64-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @Foo(i8*)
+
+define void @Bar() uwtable sanitize_address {
+entry:
+  %x = alloca [20 x i8], align 16
+  %arraydecay = getelementptr inbounds [20 x i8], [20 x i8]* %x, i64 0, i64 0
+  call void @Foo(i8* %arraydecay)
+  ret void
+}
+
+; CHECK: declare void @__asan_set_shadow_00(i64, i64)
+; CHECK: declare void @__asan_set_shadow_f1(i64, i64)
+; CHECK: declare void @__asan_set_shadow_f2(i64, i64)
+; CHECK: declare void @__asan_set_shadow_f3(i64, i64)
+; CHECK: declare void @__asan_set_shadow_f5(i64, i64)
+; CHECK: declare void @__asan_set_shadow_f8(i64, i64)
+
+; CHECK-OFF-NOT: declare void @__asan_set_shadow_