[libcxx-commits] [PATCH] D63063: Bug 42208: speeding up std::merge

[Roman Lebedev via Phabricator via libcxx-commits]

lebedev.ri added a comment.

In D63063#1536710 <https://reviews.llvm.org/D63063#1536710>, @dyaroshev wrote:

> In D63063#1535924 <https://reviews.llvm.org/D63063#1535924>, @lebedev.ri wrote:
>
> > Have you analyzed, how much is this a problem of the actual implementation (in libc++), and how much of the llvm optimization passes?
> >  I.e. are there some obvious failures of the llvm opts?
>
>
> I do not know how to get those. What do I look at?


Well, if "hey tool, give me all the optimizations that could be done here" was that easy :/

- Compile the code to `.s` (`-c -S -o test.s`), and analyze the produced assembly, interpret it "with your mind" and think if some particular assembly instruction sequences can be optimized into other, better/shorter/etc, assembly instruction sequences. This one is cpu architecture, cpu model/version specific, obviously.
- Compile the code to LLVM IR (`-c -emit-llvm -S -o test.ll`), and do the same at IR level.


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https://reviews.llvm.org/D63063