Export of internal Abseil changes

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7473df9e4922c589f6b27cf546aad097381ae552 by Martijn Vels <mvels@google.com>:

Make ABSL_ASSUME publicly available

PiperOrigin-RevId: 430540224
Change-Id: I760e2d86e3a0b676cd2a6d26e0225a77381e948f

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c83e38bc421f715b3c1e20150c2f1ffe8e633028 by Abseil Team <absl-team@google.com>:

Alias absl::bind_front to std::bind_front if available

This avoids ambiguity between the two when enabling C++20.

PiperOrigin-RevId: 430486679
GitOrigin-RevId: 7473df9e4922c589f6b27cf546aad097381ae552
Change-Id: I1e9bba09a8946480ce10ddd28e86b6c86191d38c

absl/base/optimization.h

@@ -181,22 +181,7 @@
 #define ABSL_PREDICT_TRUE(x) (x)
 #endif
 
-// ABSL_INTERNAL_ASSUME(cond)
-// Informs the compiler that 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;
-//
+// Platform and compilation mode dependent implementation of ABSL_ASSUME.
 #if !defined(NDEBUG)
 #define ABSL_INTERNAL_ASSUME(cond) assert(cond)
 #elif ABSL_HAVE_BUILTIN(__builtin_assume)
@@ -215,6 +200,24 @@
   } while (0)
 #endif
 
+// ABSL_ASSUME(cond)
+// Informs the compiler that 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 may only be evaluated
+// in some compilation modes and not others.
+//
+// Example:
+//
+//   int x = ...;
+//   ABSL_ASSUME(x >= 0);
+//   // The compiler can optimize the division to a simple right shift using the
+//   // assumption specified above.
+//   int y = x / 16;
+//
+#define ABSL_ASSUME(cond) ABSL_INTERNAL_ASSUME(cond)
+
 // ABSL_INTERNAL_UNIQUE_SMALL_NAME(cond)
 // This macro forces small unique name on a static file level symbols like
 // static local variables or static functions. This is intended to be used in

absl/container/internal/raw_hash_set.h

@@ -200,7 +200,7 @@ constexpr bool IsNoThrowSwappable(std::false_type /* is_swappable */) {
 
 template <typename T>
 uint32_t TrailingZeros(T x) {
-  ABSL_INTERNAL_ASSUME(x != 0);
+  ABSL_ASSUME(x != 0);
   return static_cast<uint32_t>(countr_zero(x));
 }
 
@@ -809,7 +809,7 @@ class raw_hash_set {
     iterator(ctrl_t* ctrl, slot_type* slot) : ctrl_(ctrl), slot_(slot) {
       // This assumption helps the compiler know that any non-end iterator is
       // not equal to any end iterator.
-      ABSL_INTERNAL_ASSUME(ctrl != nullptr);
+      ABSL_ASSUME(ctrl != nullptr);
     }
 
     void skip_empty_or_deleted() {

absl/functional/bind_front.h

@@ -30,6 +30,10 @@
 #ifndef ABSL_FUNCTIONAL_BIND_FRONT_H_
 #define ABSL_FUNCTIONAL_BIND_FRONT_H_
 
+#if defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
+#include <functional>  // For std::bind_front.
+#endif  // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
+
 #include "absl/functional/internal/front_binder.h"
 #include "absl/utility/utility.h"
 
@@ -46,7 +50,8 @@ ABSL_NAMESPACE_BEGIN
 // specified. More importantly, it provides more reliable correctness guarantees
 // than `std::bind()`; while `std::bind()` will silently ignore passing more
 // parameters than expected, for example, `absl::bind_front()` will report such
-// mis-uses as errors.
+// mis-uses as errors. In C++20, `absl::bind_front` is replaced by
+// `std::bind_front`.
 //
 // absl::bind_front(a...) can be seen as storing the results of
 // std::make_tuple(a...).
@@ -170,6 +175,9 @@ ABSL_NAMESPACE_BEGIN
 //   // Doesn't copy "hi".
 //   absl::bind_front(Print, absl::string_view(hi))("Chuk");
 //
+#if defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
+using std::bind_front;
+#else   // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
 template <class F, class... BoundArgs>
 constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
     F&& func, BoundArgs&&... args) {
@@ -177,6 +185,7 @@ constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
       absl::in_place, absl::forward<F>(func),
       absl::forward<BoundArgs>(args)...);
 }
+#endif  // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
 
 ABSL_NAMESPACE_END
 }  // namespace absl

absl/numeric/bits_benchmark.cc

@@ -59,7 +59,7 @@ static void BM_bitwidth_nonzero(benchmark::State& state) {
   while (state.KeepRunningBatch(count)) {
     for (int i = 0; i < count; ++i) {
       const T value = values[i];
-      ABSL_INTERNAL_ASSUME(value > 0);
+      ABSL_ASSUME(value > 0);
       benchmark::DoNotOptimize(value);
     }
   }

absl/numeric/int128.cc

@@ -42,11 +42,11 @@ namespace {
 //   Returns: 2
 inline ABSL_ATTRIBUTE_ALWAYS_INLINE int Fls128(uint128 n) {
   if (uint64_t hi = Uint128High64(n)) {
-    ABSL_INTERNAL_ASSUME(hi != 0);
+    ABSL_ASSUME(hi != 0);
     return 127 - countl_zero(hi);
   }
   const uint64_t low = Uint128Low64(n);
-  ABSL_INTERNAL_ASSUME(low != 0);
+  ABSL_ASSUME(low != 0);
   return 63 - countl_zero(low);
 }
 

absl/strings/internal/cord_rep_btree.h

@@ -716,7 +716,7 @@ inline void CordRepBtree::AlignBegin() {
     // size, and then do overlapping load/store of up to 4 pointers (inlined as
     // XMM, YMM or ZMM load/store) and up to 2 pointers (XMM / YMM), which is a)
     // compact and b) not clobbering any registers.
-    ABSL_INTERNAL_ASSUME(new_end <= kMaxCapacity);
+    ABSL_ASSUME(new_end <= kMaxCapacity);
 #ifdef __clang__
 #pragma unroll 1
 #endif
@@ -734,7 +734,7 @@ inline void CordRepBtree::AlignEnd() {
     const size_t new_end = end() + delta;
     set_begin(new_begin);
     set_end(new_end);
-    ABSL_INTERNAL_ASSUME(new_end <= kMaxCapacity);
+    ABSL_ASSUME(new_end <= kMaxCapacity);
 #ifdef __clang__
 #pragma unroll 1
 #endif

absl/strings/internal/str_format/arg.cc

@@ -320,7 +320,7 @@ bool ConvertIntArg(T v, const FormatConversionSpecImpl conv,
       return ConvertFloatImpl(static_cast<double>(v), conv, sink);
 
     default:
-       ABSL_INTERNAL_ASSUME(false);
+       ABSL_ASSUME(false);
   }
 
   if (conv.is_basic()) {