2 files changed, 38 insertions, 2 deletions
diff --git a/absl/base/internal/endian_test.cc b/absl/base/internal/endian_test.cc
index aa6b8496905c..678a0bf78be1 100644
--- a/absl/base/internal/endian_test.cc
+++ b/absl/base/internal/endian_test.cc
@@ -57,6 +57,7 @@ const uint16_t k16ValueBE{0x2301};
 template<typename T>
 std::vector<T> GenerateAllValuesForType() {
   std::vector<T> result;
+  result.reserve(size_t{1} << (sizeof(T) * 8));
   T next = std::numeric_limits<T>::min();
   while (true) {
     result.push_back(next);
@@ -68,10 +69,11 @@ std::vector<T> GenerateAllValuesForType() {
 }
 
 template<typename T>
-std::vector<T> GenerateRandomIntegers(size_t numValuesToTest) {
+std::vector<T> GenerateRandomIntegers(size_t num_values_to_test) {
   std::vector<T> result;
+  result.reserve(num_values_to_test);
   std::mt19937_64 rng(kRandomSeed);
-  for (size_t i = 0; i < numValuesToTest; ++i) {
+  for (size_t i = 0; i < num_values_to_test; ++i) {
     result.push_back(rng());
   }
   return result;
diff --git a/absl/base/optimization.h b/absl/base/optimization.h
index 646523b34612..1541d7a8dc31 100644
--- a/absl/base/optimization.h
+++ b/absl/base/optimization.h
@@ -178,4 +178,38 @@
 #define ABSL_PREDICT_TRUE(x) (x)
 #endif
 
+// ABSL_INTERNAL_ASSUME(cond)
+// Informs the compiler than a condition is always true and that it can assume
+// it to be true for optimization purposes. The call has undefined behavior if
+// the condition is false.
+// In !NDEBUG mode, the condition is checked with an assert().
+// NOTE: The expression must not have side effects, as it will only be evaluated
+// in some compilation modes and not others.
+//
+// Example:
+//
+//   int x = ...;
+//   ABSL_INTERNAL_ASSUME(x >= 0);
+//   // The compiler can optimize the division to a simple right shift using the
+//   // assumption specified above.
+//   int y = x / 16;
+//
+#if !defined(NDEBUG)
+#define ABSL_INTERNAL_ASSUME(cond) assert(cond)
+#elif ABSL_HAVE_BUILTIN(__builtin_assume)
+#define ABSL_INTERNAL_ASSUME(cond) __builtin_assume(cond)
+#elif defined(__GNUC__) || ABSL_HAVE_BUILTIN(__builtin_unreachable)
+#define ABSL_INTERNAL_ASSUME(cond)        \
+  do {                                    \
+    if (!(cond)) __builtin_unreachable(); \
+  } while (0)
+#elif defined(_MSC_VER)
+#define ABSL_INTERNAL_ASSUME(cond) __assume(cond)
+#else
+#define ABSL_INTERNAL_ASSUME(cond)      \
+  do {                                  \
+    static_cast<void>(false && (cond)); \
+  } while (0)
+#endif
+
 #endif  // ABSL_BASE_OPTIMIZATION_H_