Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -304,8 +304,14 @@
     c2 = (unsigned char)s2[i];
     if (c1 != c2 || c1 == '\0') break;
   }
-  COMMON_INTERCEPTOR_READ_STRING(ctx, s1, Min(i + 1, size));
-  COMMON_INTERCEPTOR_READ_STRING(ctx, s2, Min(i + 1, size));
+  uptr i1 = i;
+  uptr i2 = i;
+  if (common_flags()->strict_string_checks) {
+    for (; i1 < size && s1[i1]; i1++) {}
+    for (; i2 < size && s2[i2]; i2++) {}
+  }
+  COMMON_INTERCEPTOR_READ_RANGE((ctx), (s1), Min(i1 + 1, size));
+  COMMON_INTERCEPTOR_READ_RANGE((ctx), (s2), Min(i2 + 1, size));
   int result = CharCmpX(c1, c2);
   CALL_WEAK_INTERCEPTOR_HOOK(__sanitizer_weak_hook_strncmp, GET_CALLER_PC(), s1,
                              s2, size, result);
@@ -348,24 +354,30 @@
 }
 
 DECLARE_WEAK_INTERCEPTOR_HOOK(__sanitizer_weak_hook_strncasecmp, uptr called_pc,
-                              const char *s1, const char *s2, uptr n,
+                              const char *s1, const char *s2, uptr size,
                               int result)
 
-INTERCEPTOR(int, strncasecmp, const char *s1, const char *s2, SIZE_T n) {
+INTERCEPTOR(int, strncasecmp, const char *s1, const char *s2, SIZE_T size) {
   void *ctx;
-  COMMON_INTERCEPTOR_ENTER(ctx, strncasecmp, s1, s2, n);
+  COMMON_INTERCEPTOR_ENTER(ctx, strncasecmp, s1, s2, size);
   unsigned char c1 = 0, c2 = 0;
   uptr i;
-  for (i = 0; i < n; i++) {
+  for (i = 0; i < size; i++) {
     c1 = (unsigned char)s1[i];
     c2 = (unsigned char)s2[i];
     if (CharCaseCmp(c1, c2) != 0 || c1 == '\0') break;
   }
-  COMMON_INTERCEPTOR_READ_RANGE(ctx, s1, Min(i + 1, n));
-  COMMON_INTERCEPTOR_READ_RANGE(ctx, s2, Min(i + 1, n));
+  uptr i1 = i;
+  uptr i2 = i;
+  if (common_flags()->strict_string_checks) {
+    for (; i1 < size && s1[i1]; i1++) {}
+    for (; i2 < size && s2[i2]; i2++) {}
+  }
+  COMMON_INTERCEPTOR_READ_RANGE((ctx), (s1), Min(i1 + 1, size));
+  COMMON_INTERCEPTOR_READ_RANGE((ctx), (s2), Min(i2 + 1, size));
   int result = CharCaseCmp(c1, c2);
   CALL_WEAK_INTERCEPTOR_HOOK(__sanitizer_weak_hook_strncasecmp, GET_CALLER_PC(),
-                             s1, s2, n, result);
+                             s1, s2, size, result);
   return result;
 }
 
Index: compiler-rt/trunk/test/asan/TestCases/strncmp_strict.c
===================================================================
--- compiler-rt/trunk/test/asan/TestCases/strncmp_strict.c
+++ compiler-rt/trunk/test/asan/TestCases/strncmp_strict.c
@@ -1,26 +1,81 @@
 // Test strict_string_checks option in strncmp function
-// RUN: %clang_asan %s -o %t && %run %t 2>&1
-// RUN: %env_asan_opts=strict_string_checks=false %run %t 2>&1
-// RUN: %env_asan_opts=strict_string_checks=true not %run %t 2>&1 | FileCheck %s
+// RUN: %clang_asan %s -o %t
+
+// RUN: %env_asan_opts=strict_string_checks=false %run %t a 2>&1
+// RUN: %env_asan_opts=strict_string_checks=true %run %t a 2>&1
+// RUN: not %run %t b 2>&1 | FileCheck %s
+// RUN: not %run %t c 2>&1 | FileCheck %s
+// RUN: not %run %t d 2>&1 | FileCheck %s
+// RUN: not %run %t e 2>&1 | FileCheck %s
+// RUN: not %run %t f 2>&1 | FileCheck %s
+// RUN: not %run %t g 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=strict_string_checks=false %run %t h 2>&1
+// RUN: %env_asan_opts=strict_string_checks=true not %run %t h 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=strict_string_checks=false %run %t i 2>&1
+// RUN: %env_asan_opts=strict_string_checks=true not %run %t i 2>&1 | FileCheck %s
+
+// RUN: %env_asan_opts=strict_string_checks=false %run %t A 2>&1
+// RUN: %env_asan_opts=strict_string_checks=true %run %t A 2>&1
+// RUN: not %run %t B 2>&1 | FileCheck %s
+// RUN: not %run %t C 2>&1 | FileCheck %s
+// RUN: not %run %t D 2>&1 | FileCheck %s
+// RUN: not %run %t E 2>&1 | FileCheck %s
+// RUN: not %run %t F 2>&1 | FileCheck %s
+// RUN: not %run %t G 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=strict_string_checks=false %run %t H 2>&1
+// RUN: %env_asan_opts=strict_string_checks=true not %run %t H 2>&1 | FileCheck %s
+// RUN: %env_asan_opts=strict_string_checks=false %run %t I 2>&1
+// RUN: %env_asan_opts=strict_string_checks=true not %run %t I 2>&1 | FileCheck %s
 
 #include <assert.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
+#include <ctype.h>
 
 int main(int argc, char **argv) {
-  size_t size = 100;
+  assert(argc >= 2);
+  const size_t size = 100;
   char fill = 'o';
-  char *s1 = (char*)malloc(size);
+  char s1[size];
+  char s2[size];
   memset(s1, fill, size);
-  char *s2 = (char*)malloc(size);
   memset(s2, fill, size);
-  s1[size - 1] = 'z';
-  s2[size - 1] = 'x';
-  int r = strncmp(s1, s2, size + 1);
-  // CHECK: {{.*ERROR: AddressSanitizer: heap-buffer-overflow on address}}
-  // CHECK: READ of size 101
-  assert(r == 1);
-  free(s1);
-  free(s2);
+
+  int (*cmp_fn)(const char *, const char *, size_t);
+  cmp_fn = islower(argv[1][0]) ? &strncmp : &strncasecmp;
+
+  switch(tolower(argv[1][0])) {
+    case 'a':
+      s1[size - 1] = 'z';
+      s2[size - 1] = 'x';
+      for (int i = 0; i <= size; ++i)
+        assert((cmp_fn(s1, s2, i) == 0) == (i < size));
+      s1[size - 1] = '\0';
+      s2[size - 1] = '\0';
+      assert(cmp_fn(s1, s2, 2*size) == 0);
+      break;
+    case 'b':
+      return cmp_fn(s1-1, s2, 1);
+    case 'c':
+      return cmp_fn(s1, s2-1, 1);
+    case 'd':
+      return cmp_fn(s1+size, s2, 1);
+    case 'e':
+      return cmp_fn(s1, s2+size, 1);
+    case 'f':
+      return cmp_fn(s1+1, s2, size);
+    case 'g':
+      return cmp_fn(s1, s2+1, size);
+    case 'h':
+      s1[size - 1] = '\0';
+      assert(cmp_fn(s1, s2, 2*size) != 0);
+      break;
+    case 'i':
+      s2[size - 1] = '\0';
+      assert(cmp_fn(s1, s2, 2*size) != 0);
+      break;
+    // CHECK: {{.*}}ERROR: AddressSanitizer: stack-buffer-{{ov|und}}erflow on address
+  }
   return 0;
 }