[libcxx-commits] [libcxx] [libc++][NFC] Avoid checking that string::iterator is a contiguous iterator (PR #178636)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

<details>
<summary>Changes</summary>

`__is_continuation` is only used in contexts where we already know that the argument is a contiguous iterator. However, due to the context in which it is used, we check it as soon as the header is included. The `contiguous_iterator` check is quite expensive (~12ms on my system), so avoiding it reduces compile times for quite a few headers, including `<vector>`.


---
Full diff: https://github.com/llvm/llvm-project/pull/178636.diff


1 Files Affected:

- (modified) libcxx/include/__format/unicode.h (+1-1) 


``````````diff
diff --git a/libcxx/include/__format/unicode.h b/libcxx/include/__format/unicode.h
index 46096fda1e8ae..dbb87f2d711b0 100644
--- a/libcxx/include/__format/unicode.h
+++ b/libcxx/include/__format/unicode.h
@@ -101,7 +101,7 @@ inline constexpr __consume_result __consume_result_error{__replacement_character
   return __unicode::__is_code_point(__value) && !__unicode::__is_surrogate(__value);
 }
 
-template <contiguous_iterator _Iterator>
+template <class _Iterator>
   requires same_as<iter_value_t<_Iterator>, char>
 _LIBCPP_HIDE_FROM_ABI constexpr bool __is_continuation(_Iterator __char, int __count) {
   do {

``````````

</details>


https://github.com/llvm/llvm-project/pull/178636