[libcxx-commits] [libcxx] Reapply "[libc++] Mark __{emplace, push}_back_slow_path as noinline (#94379)" (PR #158606)

[Louis Dionne via libcxx-commits]

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@@ -1161,6 +1161,24 @@ vector<_Tp, _Allocator>::__emplace_back_slow_path(_Args&&... __args) {
   return this->__end_;
 }
 
+// This makes the compiler inline `__else()` if `__cond` is known to be false. Currently LLVM doesn't do that without
+// the `__builtin_constant_p`, since it considers `__else` unlikely even through it's known to be run.
+// See https://llvm.org/PR154292
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ldionne wrote:

I think we need to tackle this comment. If this patch makes us do worse when PGO is enabled, that's something we need to fix.

https://github.com/llvm/llvm-project/pull/158606