None of my performance concerns were relevant to this change FWIW. I think the reason that this got "fixed" was because people had a tendancy to *rely* on the name downstream when we made it always present. =/ Personally, I like having *no* names in a no-asserts build because it ensures that absolutely no one is relying on them -- we have debug information for that.
I wonder if the right way to help the debugging scenario (which is very real and painful) is to expose a flag for this, or to expose a way to take an IR file with debug info and synthesize nice names for as much as we can using the debug info? On Tue, Sep 8, 2015 at 10:47 AM David Blaikie via cfe-commits < cfe-commits@lists.llvm.org> wrote: > On Tue, Sep 8, 2015 at 10:26 AM, John McCall <rjmcc...@apple.com> wrote: > >> On Sep 8, 2015, at 8:25 AM, David Blaikie <dblai...@gmail.com> wrote: >> On Tue, Sep 8, 2015 at 2:18 AM, John McCall via cfe-commits < >> cfe-commits@lists.llvm.org> wrote: >> >>> Author: rjmccall >>> Date: Tue Sep 8 04:18:30 2015 >>> New Revision: 246991 >>> >>> URL: http://llvm.org/viewvc/llvm-project?rev=246991&view=rev >>> Log: >>> When building the alloca for a local variable, set its name >>> separately from building the instruction so that it's >>> preserved even in -Asserts builds. >>> >> >> Why do we want to preserve this name in particular in -Asserts builds? >> >> >> It’s a fairly small runtime cost — no twine appending, only present on a >> tiny fraction of instructions, unlikely to collide within a single function >> — that makes reading the IR dramatically easier. That’s still useful to be >> able to do with a production compiler, both for us and for sophisticated >> users. >> >> IIRC, Daniel did the perf work on IR names way back when; he might have >> other thoughts. >> > > *nod* I'd be curious to see/hear/better understand the tradeoffs. I know > I've talked to Chandler (CC'd) about it before when he's expressed a desire > to want to more fully remove names from non-asserts builds (specifically: > optimizations still create named values even in -Asserts builds, I think? > or maybe there was some other - oh, right, as you were saying, the Twine > building cost, even when the name isn't used some names are complex to > create, etc) > > >> >> John. >> > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >
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