Allow slow and fast abseil hardening checks to be enabled independently.

This change adds a new macro, ABSL_HARDENING_ASSERT_SLOW, which can be used for hardening assertions which have too great a performance impact to enable widely.  It also adds an additional supported value for ABSL_OPTION_HARDENED to only enable assertions which are not slow.  ABSL_OPTION_HARDENED=1 will continue to enable all hardening assertions, while ABSL_OPTION_HARDENED=2 will only enable assertions not marked as SLOW.

PiperOrigin-RevId: 668976425
Change-Id: I12cb209715d5b359c4093cc8c62e16794d7729b3

absl/base/macros.h

diff --git a/absl/base/macros.h b/absl/base/macros.h
index b318f11..ccc86ab 100644
--- a/absl/base/macros.h
+++ b/absl/base/macros.h
@@ -34,6 +34,7 @@
 #include "absl/base/attributes.h"
 #include "absl/base/config.h"
 #include "absl/base/optimization.h"
+#include "absl/base/options.h"
 #include "absl/base/port.h"
 
 // ABSL_ARRAYSIZE()
@@ -120,7 +121,7 @@
 //
 // See `ABSL_OPTION_HARDENED` in `absl/base/options.h` for more information on
 // hardened mode.
-#if ABSL_OPTION_HARDENED == 1 && defined(NDEBUG)
+#if (ABSL_OPTION_HARDENED == 1 || ABSL_OPTION_HARDENED == 2) && defined(NDEBUG)
 #define ABSL_HARDENING_ASSERT(expr)                 \
   (ABSL_PREDICT_TRUE((expr)) ? static_cast<void>(0) \
                              : [] { ABSL_INTERNAL_HARDENING_ABORT(); }())
@@ -128,6 +129,25 @@
 #define ABSL_HARDENING_ASSERT(expr) ABSL_ASSERT(expr)
 #endif
 
+// ABSL_HARDENING_ASSERT_SLOW()
+//
+// `ABSL_HARDENING_ASSERT()` is like `ABSL_HARDENING_ASSERT()`,
+//  but specifically for assertions whose predicates are too slow
+//  to be enabled in many applications.
+//
+// When `NDEBUG` is not defined, `ABSL_HARDENING_ASSERT_SLOW()` is identical to
+// `ABSL_ASSERT()`.
+//
+// See `ABSL_OPTION_HARDENED` in `absl/base/options.h` for more information on
+// hardened mode.
+#if ABSL_OPTION_HARDENED == 1 && defined(NDEBUG)
+#define ABSL_HARDENING_ASSERT_SLOW(expr)            \
+  (ABSL_PREDICT_TRUE((expr)) ? static_cast<void>(0) \
+                             : [] { ABSL_INTERNAL_HARDENING_ABORT(); }())
+#else
+#define ABSL_HARDENING_ASSERT_SLOW(expr) ABSL_ASSERT(expr)
+#endif
+
 #ifdef ABSL_HAVE_EXCEPTIONS
 #define ABSL_INTERNAL_TRY try
 #define ABSL_INTERNAL_CATCH_ANY catch (...)

absl/base/options.h

diff --git a/absl/base/options.h b/absl/base/options.h
index a169658..4b70446 100644
--- a/absl/base/options.h
+++ b/absl/base/options.h
@@ -235,7 +235,10 @@
 //
 // A value of 0 means that "hardened" mode is not enabled.
 //
-// A value of 1 means that "hardened" mode is enabled.
+// A value of 1 means that "hardened" mode is enabled with all checks.
+//
+// A value of 2 means that "hardened" mode is partially enabled, with
+// only a subset of checks chosen to minimize performance impact.
 //
 // Hardened builds have additional security checks enabled when `NDEBUG` is
 // defined. Defining `NDEBUG` is normally used to turn `assert()` macro into a