Make basic_string::operator=() tail call properly
Summary: We discovered that the compiler may chose not to inline the operator=, which leads to an expensive extra stack frame. This change makes __assign_no_alias always tail called.
Reviewers: EricWF, #libc!
Subscribers: libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D77913
Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 7ba045a430b9e3812c20a941f45addac0fd6afd7
diff --git a/include/string b/include/string
index a60ffec..6938ee4 100644
--- a/include/string
+++ b/include/string
@@ -1585,7 +1585,7 @@
// have proof that the input does not alias the current instance.
// For example, operator=(basic_string) performs a 'self' check.
template <bool __is_short>
- void __assign_no_alias(const value_type* __s, size_type __n);
+ basic_string& __assign_no_alias(const value_type* __s, size_type __n);
_LIBCPP_INLINE_VISIBILITY
void __erase_to_end(size_type __pos);
@@ -2253,7 +2253,8 @@
template <class _CharT, class _Traits, class _Allocator>
template <bool __is_short>
-void basic_string<_CharT, _Traits, _Allocator>::__assign_no_alias(
+basic_string<_CharT, _Traits, _Allocator>&
+basic_string<_CharT, _Traits, _Allocator>::__assign_no_alias(
const value_type* __s, size_type __n) {
size_type __cap = __is_short ? __min_cap : __get_long_cap();
if (__n < __cap) {
@@ -2266,6 +2267,7 @@
size_type __sz = __is_short ? __get_short_size() : __get_long_size();
__grow_by_and_replace(__cap - 1, __n - __cap + 1, __sz, 0, __sz, __n, __s);
}
+ return *this;
}
template <class _CharT, class _Traits, class _Allocator>
@@ -2340,10 +2342,10 @@
if (!__str.__is_long()) {
__r_.first().__r = __str.__r_.first().__r;
} else {
- __assign_no_alias<true>(__str.data(), __str.size());
+ return __assign_no_alias<true>(__str.data(), __str.size());
}
} else {
- __assign_no_alias<false>(__str.data(), __str.size());
+ return __assign_no_alias<false>(__str.data(), __str.size());
}
}
return *this;