Date: Wed, 6 Jan 2016 03:56:07 +0100 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: string word-at-a-time and atomic.h FAQ on twitter * Matthew Fernandez <matthew.fernandez@...ta.com.au> [2016-01-06 10:39:34 +1100]: > On 06/01/16 04:50, Rich Felker wrote: > >On Tue, Jan 05, 2016 at 05:46:41PM +0100, Szabolcs Nagy wrote: > >>... however i find lto a > >>weak excuse to rewrite strlen in asm for all targets since lto > >>of libc is still not practical ... > > This is an interesting comment; would you mind expanding on this a little? Though we don't do it > regularly, we have used LTO on Musl C in the past. I am not aware of any Musl-specific issues we > encountered, though it's entirely possible our build contained latent bugs. two things: 1) does not give the expected improvements (smaller, faster) on code that's factored well. 2) wrong code genertion (because of lto implementation bugs, or because of invalid c code) i think we saw issues around file scope inline asm, we speculated about issues around fenv access because the compilers don't model that correctly and early dynamic linker code. it is easy to imagine other nasty cases especially if gcc extensions are in use: they are often not carefully specified enough to have robust semantics with lto (e.g. attribute const for tls was an example where the semantics is unclear but lto makes it easier to break code if the user and compiler disagree) in short: i dont see the benefits given the risks.
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