forked from OSchip/llvm-project
07eb82fc06
Summary:
This change adds the macros _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT and _LIBCPP_BUILTIN_CONSTANT_P to detect compile time constants, and optimze the code accordingly.
A planned usage example:
The implementation of basic_string::assign() can short-cut a compile time known short string assignent into a fast and compact inlined assignment:
```
basic_string::assign(const value_type* __s) {
if (_LIBCPP_BUILTIN_CONSTANT_P(__s[0]) && length(__s) < __min_cap) {
copy(pointer(), _s, length(__s) + 1);
set_size(length(__s));
} else {
// delegate / tail call out of line implementation
}
}
```
Subscribers: christof, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D73732
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