[PATCH] D12355: [libcxx] Optimize away unneeded length calculation in basic_string::compare(const char*)

[Eric Fiselier via cfe-commits]

EricWF marked an inline comment as done.

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Comment at: include/string:3802
@@ -3799,2 +3801,3 @@
+    return _Traits::compare(__rhs.data(), __lhs, _VSTD::min(__lhs_len, __rhs.size())) == 0;
 }
 
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mclow.lists wrote:
> Also, you should not call `traits::compare` here. You should call `__rhs.compare(0, npos, __lhs, __lhs_len)`
> 
> which is what `__rhs.compare(__lhs)` does.
> 
I actually don't want to invoke `compare` because it has different semantics and does unneeded work. `compare` first does a comparison using  `traits::compare` and then does a comparison using `length`. We have already compared based on length and we don't need to do any of the extra work that `compare(...)` does. I think calling `__rhs.compare(0, npos, __lhs, __lhs_len)` would be a pessimization.


http://reviews.llvm.org/D12355