commit a1a09b211ec2f931d119937ca574d4befe2e303f
author George Burgess IV <gbiv@google.com> Mon May 13 17:16:20 2019 -0700
committer George Burgess IV <gbiv@google.com> Thu May 23 15:01:54 2019 -0700
tree 3f88fa5b1ec886051e1fbeee5616782b224e985e
parent 5da5dd5215b1dc2e12e0908a1c74fe0b7672835d

fortify: use __builtin_constant_p for more short-circuits

This also lets us retire our |__enable_if| version of |strlen|, which
should catch strictly fewer cases where we can fold the string's length
to a constant than |__builtin_constant_p| inside of |strlen|.

Bug: 131861088
Test: checkbuild on internal master. blueline bionic tests pass + it
      boots.
Change-Id: I21b750a24f7d1825591a88d12a385be03a0a7ca3

libc/include/bits/fortify/string.h

diff --git a/libc/include/bits/fortify/string.h b/libc/include/bits/fortify/string.h
index 426076e..af93b91 100644
--- a/libc/include/bits/fortify/string.h
+++ b/libc/include/bits/fortify/string.h
@@ -123,7 +123,7 @@
 void* memchr(const void* const s __pass_object_size, int c, size_t n) __overloadable {
     size_t bos = __bos(s);
 
-    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+    if (__bos_trivially_geq(bos, n)) {
         return __builtin_memchr(s, c, n);
     }
 
@@ -134,7 +134,7 @@
 void* __memrchr_fortify(const void* const __pass_object_size s, int c, size_t n) __overloadable {
     size_t bos = __bos(s);
 
-    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+    if (__bos_trivially_geq(bos, n)) {
         return __memrchr_real(s, c, n);
     }
 
@@ -195,24 +195,11 @@
     return __strlcat_chk(dst, src, size, bos);
 }
 
-/*
- * If we can evaluate the size of s at compile-time, just call __builtin_strlen
- * on it directly. This makes it way easier for compilers to fold things like
- * strlen("Foo") into a constant, as users would expect. -1ULL is chosen simply
- * because it's large.
- */
-__BIONIC_FORTIFY_INLINE
-size_t strlen(const char* const s __pass_object_size)
-        __overloadable __enable_if(__builtin_strlen(s) != -1ULL,
-                                   "enabled if s is a known good string.") {
-    return __builtin_strlen(s);
-}
-
 __BIONIC_FORTIFY_INLINE
 size_t strlen(const char* const s __pass_object_size0) __overloadable {
     size_t bos = __bos0(s);
 
-    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+    if (__bos_trivially_gt(bos, __builtin_strlen(s))) {
         return __builtin_strlen(s);
     }