Index: compiler-rt/lib/asan/asan_mapping.h
===================================================================
--- compiler-rt/lib/asan/asan_mapping.h
+++ compiler-rt/lib/asan/asan_mapping.h
@@ -131,7 +131,11 @@
 // || `[0x30000000, 0x35ffffff]` || LowShadow  ||
 // || `[0x00000000, 0x2fffffff]` || LowMem     ||
 
+#if defined(_ASAN_SHADOW_SCALE)
+static const u64 kDefaultShadowScale = _ASAN_SHADOW_SCALE;
+#else
 static const u64 kDefaultShadowScale = 3;
+#endif
 static const u64 kDefaultShadowSentinel = ~(uptr)0;
 static const u64 kDefaultShadowOffset32 = 1ULL << 29;  // 0x20000000
 static const u64 kDefaultShadowOffset64 = 1ULL << 44;
Index: compiler-rt/lib/asan/tests/CMakeLists.txt
===================================================================
--- compiler-rt/lib/asan/tests/CMakeLists.txt
+++ compiler-rt/lib/asan/tests/CMakeLists.txt
@@ -56,6 +56,10 @@
   -DASAN_HAS_EXCEPTIONS=1
   -DASAN_UAR=0)
 
+if(NOT LLVM_ASAN_SHADOW_SCALE EQUAL 3)
+  list(APPEND ASAN_UNITTEST_COMMON_CFLAGS -D_ASAN_SHADOW_SCALE=${LLVM_ASAN_SHADOW_SCALE})
+endif()
+
 if(APPLE)
   list(APPEND ASAN_UNITTEST_COMMON_CFLAGS ${DARWIN_osx_CFLAGS})
   list(APPEND ASAN_UNITTEST_COMMON_LINK_FLAGS ${DARWIN_osx_LINK_FLAGS})
Index: compiler-rt/test/asan/CMakeLists.txt
===================================================================
--- compiler-rt/test/asan/CMakeLists.txt
+++ compiler-rt/test/asan/CMakeLists.txt
@@ -56,6 +56,9 @@
   string(TOLOWER "-${arch}-${OS_NAME}" ASAN_TEST_CONFIG_SUFFIX)
   get_bits_for_arch(${arch} ASAN_TEST_BITS)
   get_test_cc_for_arch(${arch} ASAN_TEST_TARGET_CC ASAN_TEST_TARGET_CFLAGS)
+  if(NOT LLVM_ASAN_SHADOW_SCALE EQUAL 3)
+    set(ASAN_TEST_TARGET_CFLAGS "-D_ASAN_SHADOW_SCALE=${LLVM_ASAN_SHADOW_SCALE} ${ASAN_TEST_TARGET_CFLAGS}")
+  endif()
   if(ANDROID)
     set(ASAN_TEST_DYNAMIC True)
   else()
@@ -99,6 +102,9 @@
     pythonize_bool(ASAN_TEST_IOSSIM)
     set(ASAN_TEST_TARGET_ARCH ${arch})
     set(ASAN_TEST_TARGET_CFLAGS "-arch ${arch} -isysroot ${DARWIN_iossim_SYSROOT} ${COMPILER_RT_TEST_COMPILER_CFLAGS}")
+    if(NOT LLVM_ASAN_SHADOW_SCALE EQUAL 3)
+      set(ASAN_TEST_TARGET_CFLAGS "-D_ASAN_SHADOW_SCALE=${LLVM_ASAN_SHADOW_SCALE} ${ASAN_TEST_TARGET_CFLAGS}")
+    endif()
     set(ASAN_TEST_CONFIG_SUFFIX "-${arch}-iossim")
     get_bits_for_arch(${arch} ASAN_TEST_BITS)
     string(TOUPPER ${arch} ARCH_UPPER_CASE)
@@ -117,6 +123,9 @@
     pythonize_bool(ASAN_TEST_IOSSIM)
     set(ASAN_TEST_TARGET_ARCH ${arch})
     set(ASAN_TEST_TARGET_CFLAGS "-arch ${arch} -isysroot ${DARWIN_ios_SYSROOT} ${COMPILER_RT_TEST_COMPILER_CFLAGS}")
+    if(NOT LLVM_ASAN_SHADOW_SCALE EQUAL 3)
+      set(ASAN_TEST_TARGET_CFLAGS "-D_ASAN_SHADOW_SCALE=${LLVM_ASAN_SHADOW_SCALE} ${ASAN_TEST_TARGET_CFLAGS}")
+    endif()
     set(ASAN_TEST_CONFIG_SUFFIX "-${arch}-ios")
     get_bits_for_arch(${arch} ASAN_TEST_BITS)
     string(TOUPPER ${arch} ARCH_UPPER_CASE)
Index: llvm/CMakeLists.txt
===================================================================
--- llvm/CMakeLists.txt
+++ llvm/CMakeLists.txt
@@ -549,6 +549,14 @@
   set(LLVM_ADD_NATIVE_VISUALIZERS_TO_SOLUTION FALSE CACHE INTERNAL "For Visual Studio 2013, manually copy natvis files to Documents\\Visual Studio 2013\\Visualizers" FORCE)
 endif()
 
+set(LLVM_ASAN_SHADOW_SCALE "3"
+    CACHE STRING "The Shadow Scale to use for ASan")
+
+# Check that LLVM_ASAN_SHADOW_SCALE is supported.
+if (NOT LLVM_ASAN_SHADOW_SCALE EQUAL 3 AND NOT LLVM_ASAN_SHADOW_SCALE EQUAL 5)
+  message(FATAL_ERROR "Unsupported ASan Shadow Scale '${LLVM_ASAN_SHADOW_SCALE}' (Valid value: 3, 5)")
+endif()
+
 if (LLVM_BUILD_INSTRUMENTED OR LLVM_BUILD_INSTRUMENTED_COVERAGE OR
     LLVM_ENABLE_IR_PGO)
   if(NOT LLVM_PROFILE_MERGE_POOL_SIZE)
Index: llvm/cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- llvm/cmake/modules/HandleLLVMOptions.cmake
+++ llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -690,6 +690,10 @@
 add_definitions( -D__STDC_FORMAT_MACROS )
 add_definitions( -D__STDC_LIMIT_MACROS )
 
+if(NOT LLVM_ASAN_SHADOW_SCALE EQUAL 3)
+  add_definitions( -D_ASAN_SHADOW_SCALE=${LLVM_ASAN_SHADOW_SCALE} )
+endif()
+
 # clang doesn't print colored diagnostics when invoked from Ninja
 if (UNIX AND
     CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND
Index: llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -89,7 +89,11 @@
 
 #define DEBUG_TYPE "asan"
 
+#if defined(_ASAN_SHADOW_SCALE)
+static const uint64_t kDefaultShadowScale = _ASAN_SHADOW_SCALE;
+#else
 static const uint64_t kDefaultShadowScale = 3;
+#endif
 static const uint64_t kDefaultShadowOffset32 = 1ULL << 29;
 static const uint64_t kDefaultShadowOffset64 = 1ULL << 44;
 static const uint64_t kDynamicShadowSentinel =