[llvm-dev] [RFC] Moving llvm.dbg.value out of the instruction stream

[Reid Kleckner via llvm-dev]

On Wed, Oct 24, 2018 at 12:32 PM Chris Lattner <clattner at nondot.org> wrote:

> One other random thought: how many of these llvm.dbg.* are directly
> adjacent to each other?  It would be very simple to extend
> llvm.dbg.value/declare to be a *list* of declarations.  If many of these
> are next to each other (or are close enough, e.g. simple casts between
> them) then you could keep the per-instruction design and get the vast
> majority of the win.  This would be super incremental.
>

Yep, the stat I came up with to quantify that was that 52% of dbg.values
come in runs of length 8 or greater for this test case. The "variadic"
dbg.value idea is good, and it's come up at past BoFs and socials. I think
it captures 90% of the efficiency gains in this proposal, but doesn't
eliminate the bug class of "-g inserts dbg.values that change -O2 codegen".
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