Index: compiler-rt/trunk/lib/asan/asan_allocator.cc
===================================================================
--- compiler-rt/trunk/lib/asan/asan_allocator.cc
+++ compiler-rt/trunk/lib/asan/asan_allocator.cc
@@ -800,8 +800,12 @@
   if (!p)
     return instance.Allocate(size, 8, stack, FROM_MALLOC, true);
   if (size == 0) {
-    instance.Deallocate(p, 0, stack, FROM_MALLOC);
-    return nullptr;
+    if (flags()->allocator_frees_and_returns_null_on_realloc_zero) {
+      instance.Deallocate(p, 0, stack, FROM_MALLOC);
+      return nullptr;
+    }
+    // Allocate a size of 1 if we shouldn't free() on Realloc to 0
+    size = 1;
   }
   return instance.Reallocate(p, size, stack);
 }
Index: compiler-rt/trunk/lib/asan/asan_flags.inc
===================================================================
--- compiler-rt/trunk/lib/asan/asan_flags.inc
+++ compiler-rt/trunk/lib/asan/asan_flags.inc
@@ -148,3 +148,7 @@
           "(WARNING: USE AT YOUR OWN RISK!)")
 ASAN_FLAG(bool, use_odr_indicator, false,
           "Use special ODR indicator symbol for ODR violation detection")
+ASAN_FLAG(bool, allocator_frees_and_returns_null_on_realloc_zero, true,
+          "realloc(p, 0) is equivalent to free(p) by default (Same as the "
+          "POSIX standard). If set to false, realloc(p, 0) will return a "
+          "pointer to an allocated space which can not be used.")
Index: compiler-rt/trunk/test/asan/TestCases/realloc.cc
===================================================================
--- compiler-rt/trunk/test/asan/TestCases/realloc.cc
+++ compiler-rt/trunk/test/asan/TestCases/realloc.cc
@@ -0,0 +1,21 @@
+// RUN: %clangxx_asan -O0 %s -o %t
+// Default is true (free on realloc to 0 size)
+// RUN: %run %t 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=allocator_frees_and_returns_null_on_realloc_zero=true %run %t 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=allocator_frees_and_returns_null_on_realloc_zero=false %run %t 2>&1 | FileCheck %s --check-prefix=NO-FREE
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int main() {
+  void *p = malloc(42);
+  p = realloc(p, 0);
+  if (p) {
+    // NO-FREE: Allocated something on realloc(p, 0)
+    fprintf(stderr, "Allocated something on realloc(p, 0)\n");
+  } else {
+    // CHECK: realloc(p, 0) returned nullptr
+    fprintf(stderr, "realloc(p, 0) returned nullptr\n");
+  }
+  free(p);
+}