[libcxx-commits] [libcxx] [libc++] Make _LIBCPP_ASSUME usable when it is appropriate (PR #91801)

[David Benjamin via libcxx-commits]

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@@ -23,17 +23,20 @@
        : _LIBCPP_ASSERTION_HANDLER(__FILE__ ":" _LIBCPP_TOSTRING(__LINE__) ": assertion " _LIBCPP_TOSTRING(            \
              expression) " failed: " message "\n"))
 
-// TODO: __builtin_assume can currently inhibit optimizations. Until this has been fixed and we can add
-//       assumptions without a clear optimization intent, disable that to avoid worsening the code generation.
-//       See https://discourse.llvm.org/t/llvm-assume-blocks-optimization/71609 for a discussion.
-#if 0 && __has_builtin(__builtin_assume)
+// WARNING: __builtin_assume can currently inhibit optimizations. Only add assumptions with a clear
+// optimization intent. See https://discourse.llvm.org/t/llvm-assume-blocks-optimization/71609 for a
+// discussion.
+#if __has_builtin(__builtin_assume)
 #  define _LIBCPP_ASSUME(expression)                                                                                   \
     (_LIBCPP_DIAGNOSTIC_PUSH _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wassume")                                              \
          __builtin_assume(static_cast<bool>(expression)) _LIBCPP_DIAGNOSTIC_POP)
 #else
 #  define _LIBCPP_ASSUME(expression) ((void)0)
 #endif
 
+// Historically, disabled assertions below expanded to `_LIBCPP_ASSUME`, but this both triggers the
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davidben wrote:

Removed and rebased.

https://github.com/llvm/llvm-project/pull/91801